Implemented LDAP component of GPO-based access control

Reviewed-by: Sumit Bose <sbose@redhat.com>
Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>

1 files changed, 2248 insertions, 0 deletions

diff --git a/src/providers/ad/ad_gpo.c b/src/providers/ad/ad_gpo.c
new file mode 100644
index 000000000..ca8a5f66c
--- /dev/null
+++ b/src/providers/ad/ad_gpo.c
@@ -0,0 +1,2248 @@
+/*
+    SSSD
+
+    Authors:
+        Yassir Elley <yelley@redhat.com>
+
+    Copyright (C) 2013 Red Hat
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+/*
+ * This file implements the following pair of *public* functions (see header):
+ *   ad_gpo_access_send/recv: provides client-side GPO processing
+ *
+ * This file also implements the following pairs of *private* functions (which
+ * are used by the public functions):
+ *   ad_gpo_process_som_send/recv: populate list of gp_som objects
+ *   ad_gpo_process_gpo_send/recv: populate list of gp_gpo objects
+ */
+
+#include <security/pam_modules.h>
+#include "util/util.h"
+#include "util/strtonum.h"
+#include "providers/data_provider.h"
+#include "providers/dp_backend.h"
+#include "providers/ad/ad_access.h"
+#include "providers/ad/ad_common.h"
+#include "providers/ad/ad_domain_info.h"
+#include "providers/ad/ad_gpo.h"
+#include "providers/ldap/sdap_access.h"
+#include "providers/ldap/sdap_async.h"
+#include "providers/ldap/sdap.h"
+#include <ndr.h>
+#include <gen_ndr/security.h>
+
+#define AD_AT_DN "distinguishedName"
+#define AD_AT_UAC "userAccountControl"
+#define AD_AT_CONFIG_NC "configurationNamingContext"
+#define AD_AT_GPLINK "gPLink"
+#define AD_AT_GPOPTIONS "gpOptions"
+#define AD_AT_NT_SEC_DESC "nTSecurityDescriptor"
+#define AD_AT_CN "cn"
+#define AD_AT_DISPLAY_NAME "displayName"
+#define AD_AT_FILE_SYS_PATH "gPCFileSysPath"
+#define AD_AT_VERSION_NUMBER "versionNumber"
+#define AD_AT_MACHINE_EXT_NAMES "gPCMachineExtensionNames"
+#define AD_AT_USER_EXT_NAMES "gPCUserExtensionNames"
+#define AD_AT_FUNC_VERSION "gPCFunctionalityVersion"
+#define AD_AT_FLAGS "flags"
+
+#define UAC_WORKSTATION_TRUST_ACCOUNT 0x00001000
+#define AD_AGP_GUID "edacfd8f-ffb3-11d1-b41d-00a0c968f939"
+#define AD_AUTHENTICATED_USERS_SID "S-1-5-11"
+#define SID_MAX_LEN 1024
+
+/* == common data structures and declarations ============================= */
+
+struct gp_som {
+    const char *som_dn;
+    struct gp_gplink **gplink_list;
+    int num_gplinks;
+};
+
+struct gp_gplink {
+    const char *gpo_dn;
+    bool enforced;
+};
+
+struct gp_gpo {
+    struct security_descriptor *gpo_sd;
+    const char *gpo_dn;
+    const char *gpo_guid;
+    const char *gpo_display_name;
+    const char *gpo_file_sys_path;
+    uint32_t gpo_container_version;
+    const char **gpo_cse_guids;
+    int num_gpo_cse_guids;
+    int gpo_func_version;
+    int gpo_flags;
+};
+
+enum ace_eval_status {
+    AD_GPO_ACE_DENIED,
+    AD_GPO_ACE_ALLOWED,
+    AD_GPO_ACE_NEUTRAL
+};
+
+struct tevent_req *ad_gpo_process_som_send(TALLOC_CTX *mem_ctx,
+                                           struct tevent_context *ev,
+                                           struct sdap_id_conn_ctx *conn,
+                                           struct ldb_context *ldb_ctx,
+                                           struct sdap_id_op *sdap_op,
+                                           struct sdap_options *opts,
+                                           int timeout,
+                                           const char *target_dn,
+                                           const char *domain_name);
+int ad_gpo_process_som_recv(struct tevent_req *req,
+                            TALLOC_CTX *mem_ctx,
+                            struct gp_som ***som_list);
+
+struct tevent_req *ad_gpo_process_gpo_send(TALLOC_CTX *mem_ctx,
+                                           struct tevent_context *ev,
+                                           struct sdap_id_op *sdap_op,
+                                           struct sdap_options *opts,
+                                           int timeout,
+                                           struct gp_som **som_list);
+int ad_gpo_process_gpo_recv(struct tevent_req *req,
+                            TALLOC_CTX *mem_ctx,
+                            struct gp_gpo ***candidate_gpos,
+                            int *num_candidate_gpos);
+
+/* == ad_gpo_access_send/recv helpers =======================================*/
+
+/*
+ * This function retrieves the SIDs corresponding to the input user and returns
+ * the user_sid, group_sids, and group_size in their respective output params.
+ *
+ * Note: since authentication must complete successfully before the
+ * gpo access checks are called, we can safely assume that the user/computer
+ * has been authenticated. As such, this function always adds the
+ * AD_AUTHENTICATED_USERS_SID to the group_sids.
+ */
+static errno_t
+ad_gpo_get_sids(TALLOC_CTX *mem_ctx,
+                const char *user,
+                struct sss_domain_info *domain,
+                const char **_user_sid,
+                const char ***_group_sids,
+                int *_group_size)
+{
+    TALLOC_CTX *tmp_ctx = NULL;
+    struct ldb_result *res;
+    int ret = 0;
+    int i = 0;
+    int num_group_sids = 0;
+    const char *user_sid = NULL;
+    const char *group_sid = NULL;
+    const char **group_sids = NULL;
+
+    tmp_ctx = talloc_new(NULL);
+    if (tmp_ctx == NULL) {
+        ret = ENOMEM;
+        goto done;
+    }
+
+    /* first result from sysdb_initgroups is user_sid; rest are group_sids */
+    ret = sysdb_initgroups(tmp_ctx, domain, user, &res);
+    if (ret != EOK) {
+        DEBUG(SSSDBG_OP_FAILURE,
+              "sysdb_initgroups failed: [%d](%s)\n",
+              ret, sss_strerror(ret));
+        return ret;
+    }
+
+    if (res->count == 0) {
+        ret = ENOENT;
+        DEBUG(SSSDBG_OP_FAILURE,
+              "sysdb_initgroups returned empty result\n");
+        return ret;
+    }
+
+    user_sid = ldb_msg_find_attr_as_string(res->msgs[0], SYSDB_SID_STR, NULL);
+    num_group_sids = (res->count) - 1;
+
+    /* include space for AD_AUTHENTICATED_USERS_SID and NULL */
+    group_sids = talloc_array(tmp_ctx, const char *, num_group_sids + 1 + 1);
+    if (group_sids == NULL) {
+        ret = ENOMEM;
+        goto done;
+    }
+
+    for (i = 0; i < num_group_sids; i++) {
+        group_sid = ldb_msg_find_attr_as_string(res->msgs[i+1],
+                                                SYSDB_SID_STR, NULL);
+        if (group_sid == NULL) {
+            continue;
+        }
+
+        group_sids[i] = talloc_steal(group_sids, group_sid);
+        if (group_sids[i] == NULL) {
+            ret = ENOMEM;
+            goto done;
+        }
+    }
+    group_sids[i++] = talloc_strdup(group_sids, AD_AUTHENTICATED_USERS_SID);
+    group_sids[i] = NULL;
+
+    *_group_size = num_group_sids + 1;
+    *_group_sids = talloc_steal(mem_ctx, group_sids);
+    *_user_sid = talloc_steal(mem_ctx, user_sid);
+    return EOK;
+
+ done:
+    talloc_free(tmp_ctx);
+    return ret;
+}
+
+bool string_to_sid(struct dom_sid *sidout, const char *sidstr);
+int dom_sid_string_buf(const struct dom_sid *sid, char *buf, int buflen);
+bool dom_sid_equal(const struct dom_sid *sid1, const struct dom_sid *sid2);
+
+/*
+ * This function determines whether the input ACE includes any of the
+ * client's SIDs. The boolean result is assigned to the _included output param.
+ */
+static errno_t
+ad_gpo_ace_includes_client_sid(const char *user_sid,
+                               const char **group_sids,
+                               int group_size,
+                               struct security_ace *ace,
+                               bool *_included)
+{
+    int i = 0;
+    struct dom_sid ace_dom_sid;
+    struct dom_sid user_dom_sid;
+    struct dom_sid group_dom_sid;
+    char buf[SID_MAX_LEN + 1];
+
+    ace_dom_sid = ace->trustee;
+
+    dom_sid_string_buf(&ace_dom_sid, buf, SID_MAX_LEN);
+
+    if (!string_to_sid(&user_dom_sid, user_sid)) {
+        DEBUG(SSSDBG_OP_FAILURE, "string_to_sid failed\n");
+        return EINVAL;
+    }
+
+    if (dom_sid_equal(&ace_dom_sid, &user_dom_sid)) {
+        *_included = true;
+        return EOK;
+    }
+
+    for (i = 0; i < group_size; i++) {
+        if (!string_to_sid(&group_dom_sid, group_sids[i])) {
+            DEBUG(SSSDBG_OP_FAILURE, "string_to_sid failed\n");
+            return EINVAL;
+        }
+        if (dom_sid_equal(&ace_dom_sid, &group_dom_sid)) {
+            *_included = true;
+            return EOK;
+        }
+    }
+
+    *_included = false;
+    return EOK;
+}
+
+/*
+ * This function determines whether use of the extended right
+ * named "ApplyGroupPolicy" (AGP) is allowed, by comparing the specified
+ * user_sid and group_sids against the specified access control entry (ACE).
+ * This function returns ALLOWED, DENIED, or NEUTRAL depending on whether
+ * the ACE explictly allows, explicitly denies, or does neither.
+ *
+ * Note that the 'M' abbreviation used in the evaluation algorithm stands for
+ * "access_mask", which represents the set of access rights associated with an
+ * individual ACE. The access right of interest to the GPO code is
+ * RIGHT_DS_CONTROL_ACCESS, which serves as a container for all control access
+ * rights. The specific control access right is identified by a GUID in the
+ * ACE's ObjectType. In our case, this is the GUID corresponding to AGP.
+ *
+ * The ACE evaluation algorithm is specified in [MS-ADTS] 5.1.3.3.4:
+ * - Deny access by default
+ * - If the "Inherit Only" (IO) flag is set in the ACE, skip the ACE.
+ * - If the SID in the ACE does not match any SID in the requester's
+ *   security context, skip the ACE
+ * - If the ACE type is "Object Access Allowed", the access right
+ *   RIGHT_DS_CONTROL_ACCESS (CR) is present in M, and the ObjectType
+ *   field in the ACE is either not present OR contains a GUID value equal
+ *   to AGP, then grant requested control access right. Stop access checking.
+ * - If the ACE type is "Object Access Denied", the access right
+ *   RIGHT_DS_CONTROL_ACCESS (CR) is present in M, and the ObjectType
+ *   field in the ACE is either not present OR contains a GUID value equal to
+ *   AGP, then deny the requested control access right. Stop access checking.
+ */
+static enum ace_eval_status ad_gpo_evaluate_ace(struct security_ace *ace,
+                                                const char *user_sid,
+                                                const char **group_sids,
+                                                int group_size)
+{
+    bool agp_included = false;
+    bool included = false;
+    int ret = 0;
+    struct security_ace_object object;
+    struct GUID ext_right_agp_guid;
+
+    if (ace->flags & SEC_ACE_FLAG_INHERIT_ONLY) {
+        return AD_GPO_ACE_NEUTRAL;
+    }
+
+    ret = ad_gpo_ace_includes_client_sid(user_sid, group_sids, group_size, ace,
+                                         &included);
+    if (ret != EOK) {
+        return AD_GPO_ACE_DENIED;
+    }
+
+    if (!included) {
+        return AD_GPO_ACE_NEUTRAL;
+    }
+
+    object = ace->object.object;
+    GUID_from_string(AD_AGP_GUID, &ext_right_agp_guid);
+
+    if (object.flags & SEC_ACE_OBJECT_TYPE_PRESENT) {
+        if (GUID_equal(&object.type.type, &ext_right_agp_guid)) {
+            agp_included = true;
+        }
+    } else {
+        agp_included = false;
+    }
+
+    if (ace->access_mask & SEC_ADS_CONTROL_ACCESS) {
+        if (agp_included) {
+            if (ace->type == SEC_ACE_TYPE_ACCESS_ALLOWED_OBJECT) {
+                return AD_GPO_ACE_ALLOWED;
+            } else if (ace->type == SEC_ACE_TYPE_ACCESS_DENIED_OBJECT) {
+                return AD_GPO_ACE_DENIED;
+            }
+        }
+    }
+
+    return AD_GPO_ACE_DENIED;
+}
+
+/*
+ * This function extracts the GPO's DACL (discretionary access control list)
+ * from the GPO's specified security descriptor, and determines whether
+ * the GPO is applicable to the policy target, by comparing the specified
+ * user_sid and group_sids against each access control entry (ACE) in the DACL.
+ * The boolean result is assigned to the _access_allowed output parameter.
+ */
+static errno_t ad_gpo_evaluate_dacl(struct security_acl *dacl,
+                                    const char *user_sid,
+                                    const char **group_sids,
+                                    int group_size,
+                                    bool *_dacl_access_allowed)
+{
+    uint32_t num_aces = 0;
+    enum ace_eval_status ace_status;
+    int i = 0;
+    struct security_ace *ace = NULL;
+
+    num_aces = dacl->num_aces;
+
+    /*
+     * [MS-ADTS] 5.1.3.3.4:
+     * If the DACL does not have any ACE, then deny the requester the
+     * requested control access right.
+     */
+    if (num_aces == 0) {
+        *_dacl_access_allowed = false;
+        return EOK;
+    }
+
+    for (i = 0; i < dacl->num_aces; i ++) {
+        ace = &dacl->aces[i];
+
+        ace_status = ad_gpo_evaluate_ace(ace, user_sid, group_sids, group_size);
+
+        switch (ace_status) {
+        case AD_GPO_ACE_NEUTRAL:
+            continue;
+        case AD_GPO_ACE_ALLOWED:
+            *_dacl_access_allowed = true;
+            return EOK;
+        case AD_GPO_ACE_DENIED:
+            *_dacl_access_allowed = false;
+            return EOK;
+        }
+    }
+
+    *_dacl_access_allowed = false;
+    return EOK;
+}
+
+/*
+ * This function takes candidate_gpos as input, filters out any gpo that is
+ * not applicable to the policy target and assigns the result to the
+ * _dacl_filtered_gpos output parameter. The filtering algorithm is
+ * defined in [MS-GPOL] 3.2.5.1.6
+ */
+
+static errno_t
+ad_gpo_filter_gpos_by_dacl(TALLOC_CTX *mem_ctx,
+                           const char *user,
+                           struct sss_domain_info *domain,
+                           struct gp_gpo **candidate_gpos,
+                           int num_candidate_gpos,
+                           struct gp_gpo ***_dacl_filtered_gpos,
+                           int *_num_dacl_filtered_gpos)
+{
+    TALLOC_CTX *tmp_ctx = NULL;
+    int i = 0;
+    int ret = 0;
+    struct gp_gpo *candidate_gpo = NULL;
+    struct security_descriptor *sd = NULL;
+    struct security_acl *dacl = NULL;
+    const char *user_sid = NULL;
+    const char **group_sids = NULL;
+    int group_size = 0;
+    int gpo_dn_idx = 0;
+    bool access_allowed = false;
+    struct gp_gpo **dacl_filtered_gpos = NULL;
+
+    tmp_ctx = talloc_new(NULL);
+    if (tmp_ctx == NULL) {
+        ret = ENOMEM;
+        goto done;
+    }
+
+    ret = ad_gpo_get_sids(tmp_ctx, user, domain, &user_sid,
+                          &group_sids, &group_size);
+    if (ret != EOK) {
+        ret = ERR_NO_SIDS;
+        DEBUG(SSSDBG_OP_FAILURE,
+              "Unable to retrieve SIDs: [%d](%s)\n", ret, sss_strerror(ret));
+        goto done;
+    }
+
+    dacl_filtered_gpos = talloc_array(tmp_ctx,
+                                 struct gp_gpo *,
+                                 num_candidate_gpos + 1);
+
+    if (dacl_filtered_gpos == NULL) {
+        ret = ENOMEM;
+        goto done;
+    }
+
+    for (i = 0; i < num_candidate_gpos; i++) {
+
+        access_allowed = false;
+        candidate_gpo = candidate_gpos[i];
+        sd = candidate_gpo->gpo_sd;
+        dacl = candidate_gpo->gpo_sd->dacl;
+
+        DEBUG(SSSDBG_TRACE_ALL, "examining dacl candidate_gpo_guid:%s\n",
+                                candidate_gpo->gpo_guid);
+
+        /* gpo_func_version must be set to version 2 */
+        if (candidate_gpo->gpo_func_version != 2) {
+            DEBUG(SSSDBG_TRACE_ALL,
+                  "GPO not applicable to target per security filtering\n");
+            continue;
+        }
+
+        /* gpo_flags value of 2 means that GPO's computer portion is disabled */
+        if (candidate_gpo->gpo_flags == 2) {
+            DEBUG(SSSDBG_TRACE_ALL,
+                  "GPO not applicable to target per security filtering\n");
+            continue;
+        }
+
+        /*
+         * [MS-ADTS] 5.1.3.3.4:
+         * If the security descriptor has no DACL or its "DACL Present" bit
+         * is not set, then grant requester the requested control access right.
+         */
+
+        if ((!(sd->type & SEC_DESC_DACL_PRESENT)) || (dacl == NULL)) {
+            DEBUG(SSSDBG_TRACE_ALL, "DACL is not present\n");
+            access_allowed = true;
+            break;
+        }
+
+        ad_gpo_evaluate_dacl(dacl, user_sid, group_sids,
+                             group_size, &access_allowed);
+        if (access_allowed) {
+            DEBUG(SSSDBG_TRACE_ALL,
+                  "GPO applicable to target per security filtering\n");
+            dacl_filtered_gpos[gpo_dn_idx] = talloc_steal(dacl_filtered_gpos,
+                                                          candidate_gpo);
+            gpo_dn_idx++;
+        } else {
+            DEBUG(SSSDBG_TRACE_ALL,
+                  "GPO not applicable to target per security filtering\n");
+            continue;
+        }
+    }
+
+    dacl_filtered_gpos[gpo_dn_idx] = NULL;
+
+    *_dacl_filtered_gpos = talloc_steal(mem_ctx, dacl_filtered_gpos);
+    *_num_dacl_filtered_gpos = gpo_dn_idx;
+
+    ret = EOK;
+
+ done:
+    talloc_free(tmp_ctx);
+    return ret;
+}
+
+/* == ad_gpo_access_send/recv implementation ================================*/
+
+struct ad_gpo_access_state {
+    struct tevent_context *ev;
+    struct ldb_context *ldb_ctx;
+    struct sdap_id_conn_ctx *conn;
+    struct sdap_id_op *sdap_op;
+    struct sdap_options *opts;
+    int timeout;
+    struct sss_domain_info *domain;
+    const char *user;
+    const char *ad_hostname;
+    const char *target_dn;
+    struct gp_gpo **dacl_filtered_gpos;
+    int num_dacl_filtered_gpos;
+};
+
+static void ad_gpo_connect_done(struct tevent_req *subreq);
+static void ad_gpo_target_dn_retrieval_done(struct tevent_req *subreq);
+static void ad_gpo_process_som_done(struct tevent_req *subreq);
+static void ad_gpo_process_gpo_done(struct tevent_req *subreq);
+
+struct tevent_req *
+ad_gpo_access_send(TALLOC_CTX *mem_ctx,
+                   struct tevent_context *ev,
+                   struct sss_domain_info *domain,
+                   struct ad_access_ctx *ctx,
+                   const char *user)
+{
+    struct tevent_req *req;
+    struct tevent_req *subreq;
+    struct ad_gpo_access_state *state;
+    errno_t ret;
+
+    req = tevent_req_create(mem_ctx, &state, struct ad_gpo_access_state);
+    if (req == NULL) {
+        DEBUG(SSSDBG_CRIT_FAILURE, "tevent_req_create() failed\n");
+        return NULL;
+    }
+
+    state->domain = domain;
+    state->dacl_filtered_gpos = NULL;
+    state->num_dacl_filtered_gpos = 0;
+    state->ev = ev;
+    state->user = user;
+    state->ldb_ctx = sysdb_ctx_get_ldb(domain->sysdb);
+    state->ad_hostname = dp_opt_get_string(ctx->ad_options, AD_HOSTNAME);
+    state->opts = ctx->sdap_access_ctx->id_ctx->opts;
+    state->timeout = dp_opt_get_int(state->opts->basic, SDAP_SEARCH_TIMEOUT);
+    state->conn = ad_get_dom_ldap_conn(ctx->ad_id_ctx, domain);
+    state->sdap_op = sdap_id_op_create(state, state->conn->conn_cache);
+    if (state->sdap_op == NULL) {
+        DEBUG(SSSDBG_OP_FAILURE, "sdap_id_op_create failed.\n");
+        ret = ENOMEM;
+        goto immediately;
+    }
+
+    subreq = sdap_id_op_connect_send(state->sdap_op, state, &ret);
+    if (subreq == NULL) {
+        DEBUG(SSSDBG_OP_FAILURE,
+              "sdap_id_op_connect_send failed: [%d](%s)\n",
+               ret, sss_strerror(ret));
+        goto immediately;
+    }
+    tevent_req_set_callback(subreq, ad_gpo_connect_done, req);
+
+    ret = EOK;
+
+immediately:
+
+    if (ret != EOK) {
+        tevent_req_error(req, ret);
+        tevent_req_post(req, ev);
+    }
+
+    return req;
+}
+
+static void
+ad_gpo_connect_done(struct tevent_req *subreq)
+{
+    struct tevent_req *req;
+    struct ad_gpo_access_state *state;
+    char* filter;
+    char *sam_account_name;
+    char *domain_dn;
+    int dp_error;
+    errno_t ret;
+
+    const char *attrs[] = {AD_AT_DN, AD_AT_UAC, NULL};
+
+    req = tevent_req_callback_data(subreq, struct tevent_req);
+    state = tevent_req_data(req, struct ad_gpo_access_state);
+
+    ret = sdap_id_op_connect_recv(subreq, &dp_error);
+    talloc_zfree(subreq);
+
+    if (ret != EOK) {
+        /* TBD: handle (dp_error == DP_ERR_OFFLINE) case */
+
+        DEBUG(SSSDBG_OP_FAILURE,
+              "Failed to connect to AD server: [%d](%s)\n",
+               ret, sss_strerror(ret));
+
+        tevent_req_error(req, ret);
+        return;
+    }
+
+    sam_account_name = talloc_asprintf(state, "%s$", state->ad_hostname);
+    if (sam_account_name == NULL) {
+        tevent_req_error(req, ENOMEM);
+        return;
+    }
+
+    DEBUG(SSSDBG_TRACE_FUNC, "sam_account_name is %s\n", sam_account_name);
+
+    /* Convert the domain name into domain DN */
+    ret = domain_to_basedn(state, state->domain->name, &domain_dn);
+    if (ret != EOK) {
+        DEBUG(SSSDBG_OP_FAILURE,
+              "Cannot convert domain name [%s] to base DN [%d]: %s\n",
+               state->domain->name, ret, sss_strerror(ret));
+        tevent_req_error(req, ret);
+        return;
+    }
+
+    /* SDAP_OC_USER objectclass covers both users and computers */
+    filter = talloc_asprintf(state,
+                             "(&(objectclass=%s)(%s=%s))",
+                             state->opts->user_map[SDAP_OC_USER].name,
+                             state->opts->user_map[SDAP_AT_USER_NAME].name,
+                             sam_account_name);
+
+    if (filter == NULL) {
+        tevent_req_error(req, ENOMEM);
+        return;
+    }
+
+    subreq = sdap_get_generic_send(state, state->ev, state->opts,
+                                   sdap_id_op_handle(state->sdap_op),
+                                   domain_dn, LDAP_SCOPE_SUBTREE,
+                                   filter, attrs, NULL, 0,
+                                   state->timeout,
+                                   false);
+
+    if (subreq == NULL) {
+        DEBUG(SSSDBG_OP_FAILURE, "sdap_get_generic_send failed.\n");
+        tevent_req_error(req, EIO);
+        return;
+    }
+
+    tevent_req_set_callback(subreq, ad_gpo_target_dn_retrieval_done, req);
+}
+
+static void
+ad_gpo_target_dn_retrieval_done(struct tevent_req *subreq)
+{
+    struct tevent_req *req;
+    struct ad_gpo_access_state *state;
+    int ret;
+    int dp_error;
+    size_t reply_count;
+    struct sysdb_attrs **reply;
+    const char *target_dn = NULL;
+    uint32_t uac;
+
+    req = tevent_req_callback_data(subreq, struct tevent_req);
+    state = tevent_req_data(req, struct ad_gpo_access_state);
+    ret = sdap_get_generic_recv(subreq, state,
+                                &reply_count, &reply);
+    talloc_zfree(subreq);
+    if (ret != EOK) {
+        ret = sdap_id_op_done(state->sdap_op, ret, &dp_error);
+        /* TBD: handle (dp_error == DP_ERR_OFFLINE) case */
+
+        DEBUG(SSSDBG_OP_FAILURE,
+              "Unable to get policy target's DN: [%d](%s)\n",
+               ret, sss_strerror(ret));
+        ret = ENOENT;
+        goto done;
+    }
+
+    /* make sure there is only one non-NULL reply returned */
+
+    if (reply_count < 1) {
+        DEBUG(SSSDBG_OP_FAILURE, "No DN retrieved for policy target.\n");
+        ret = ENOENT;
+        goto done;
+    } else if (reply_count > 1) {
+        DEBUG(SSSDBG_OP_FAILURE, "Multiple replies for policy target\n");
+        ret = ERR_INTERNAL;
+        goto done;
+    } else if (reply == NULL) {
+        DEBUG(SSSDBG_OP_FAILURE, "reply_count is 1, but reply is NULL\n");
+        ret = ERR_INTERNAL;
+        goto done;
+    }
+
+    /* reply[0] holds requested attributes of single reply */
+    ret = sysdb_attrs_get_string(reply[0], AD_AT_DN, &target_dn);
+    if (ret != EOK) {
+        DEBUG(SSSDBG_OP_FAILURE,
+              "sysdb_attrs_get_string failed: [%d](%s)\n",
+               ret, sss_strerror(ret));
+        goto done;
+    }
+
+    state->target_dn = talloc_steal(state, target_dn);
+    if (state->target_dn == NULL) {
+        ret = ENOMEM;
+        goto done;
+    }
+
+    ret = sysdb_attrs_get_uint32_t(reply[0], AD_AT_UAC, &uac);
+    if (ret != EOK) {
+        DEBUG(SSSDBG_OP_FAILURE,
+              "sysdb_attrs_get_uint32_t failed: [%d](%s)\n",
+               ret, sss_strerror(ret));
+        goto done;
+    }
+
+    /* we only support computer policy targets, not users */
+    if (!(uac & UAC_WORKSTATION_TRUST_ACCOUNT)) {
+        ret = EINVAL;
+        goto done;
+    }
+
+    subreq = ad_gpo_process_som_send(state,
+                                     state->ev,
+                                     state->conn,
+                                     state->ldb_ctx,
+                                     state->sdap_op,
+                                     state->opts,
+                                     state->timeout,
+                                     state->target_dn,
+                                     state->domain->name);
+    if (subreq == NULL) {
+        ret = ENOMEM;
+        goto done;
+    }
+
+    tevent_req_set_callback(subreq, ad_gpo_process_som_done, req);
+
+    ret = EOK;
+
+ done:
+
+    if (ret != EOK) {
+        tevent_req_error(req, ret);
+    }
+}
+
+static void
+ad_gpo_process_som_done(struct tevent_req *subreq)
+{
+    struct tevent_req *req;
+    struct ad_gpo_access_state *state;
+    int ret;
+    struct gp_som **som_list;
+
+    req = tevent_req_callback_data(subreq, struct tevent_req);
+    state = tevent_req_data(req, struct ad_gpo_access_state);
+    ret = ad_gpo_process_som_recv(subreq, state, &som_list);
+    talloc_zfree(subreq);
+
+    if (ret != EOK) {
+        DEBUG(SSSDBG_OP_FAILURE,
+              "Unable to get som list: [%d](%s)\n",
+               ret, sss_strerror(ret));
+        ret = ENOENT;
+        goto done;
+    }
+
+    subreq = ad_gpo_process_gpo_send(state,
+                                     state->ev,
+                                     state->sdap_op,
+                                     state->opts,
+                                     state->timeout,
+                                     som_list);
+    if (subreq == NULL) {
+        ret = ENOMEM;
+        goto done;
+    }
+
+    tevent_req_set_callback(subreq, ad_gpo_process_gpo_done, req);
+
+    ret = EOK;
+
+ done:
+
+    if (ret != EOK) {
+        tevent_req_error(req, ret);
+    }
+}
+
+/*
+ * This function retrieves a list of candidate_gpos and potentially reduces it
+ * to a list of dacl_filtered_gpos, based on each GPO's DACL.
+ */
+static void
+ad_gpo_process_gpo_done(struct tevent_req *subreq)
+{
+    struct tevent_req *req;
+    struct ad_gpo_access_state *state;
+    int ret;
+    int dp_error;
+    struct gp_gpo **candidate_gpos = NULL;
+    int num_candidate_gpos = 0;
+    int i = 0;
+
+    req = tevent_req_callback_data(subreq, struct tevent_req);
+    state = tevent_req_data(req, struct ad_gpo_access_state);
+    ret = ad_gpo_process_gpo_recv(subreq, state, &candidate_gpos,
+                                  &num_candidate_gpos);
+
+    talloc_zfree(subreq);
+
+    ret = sdap_id_op_done(state->sdap_op, ret, &dp_error);
+
+    if (ret != EOK) {
+        /* TBD: handle (dp_error == DP_ERR_OFFLINE) case */
+
+        DEBUG(SSSDBG_OP_FAILURE,
+              "Unable to get GPO list: [%d](%s)\n",
+              ret, sss_strerror(ret));
+        ret = ENOENT;
+        goto done;
+    }
+
+    ret = ad_gpo_filter_gpos_by_dacl(state, state->user, state->domain,
+                                     candidate_gpos, num_candidate_gpos,
+                                     &state->dacl_filtered_gpos,
+                                     &state->num_dacl_filtered_gpos);
+    if (ret != EOK) {
+        DEBUG(SSSDBG_OP_FAILURE,
+              "Unable to filter GPO list: [%d](%s)\n",
+              ret, sss_strerror(ret));
+        goto done;
+    }
+
+    if (state->dacl_filtered_gpos[0] == NULL) {
+        /* since no applicable gpos were found, there is nothing to enforce */
+        DEBUG(SSSDBG_TRACE_FUNC,
+              "no applicable gpos found after dacl filtering\n");
+        ret = EOK;
+        goto done;
+    }
+
+    for (i = 0; i < state->num_dacl_filtered_gpos; i++) {
+        DEBUG(SSSDBG_TRACE_FUNC, "dacl_filtered_gpos[%d]->gpo_guid is %s\n", i,
+              state->dacl_filtered_gpos[i]->gpo_guid);
+    }
+
+    /* TBD: initiate SMB retrieval */
+    DEBUG(SSSDBG_TRACE_FUNC, "time for SMB retrieval\n");
+
+    ret = EOK;
+
+ done:
+
+    if (ret == EOK) {
+        tevent_req_done(req);
+    } else if (ret != EAGAIN) {
+        tevent_req_error(req, ret);
+    }
+}
+
+errno_t
+ad_gpo_access_recv(struct tevent_req *req)
+{
+    TEVENT_REQ_RETURN_ON_ERROR(req);
+
+    return EOK;
+}
+
+/* == ad_gpo_process_som_send/recv helpers ================================= */
+
+/*
+ * This function returns the parent of an LDAP DN
+ */
+static errno_t
+ad_gpo_parent_dn(TALLOC_CTX *mem_ctx,
+                 struct ldb_context *ldb_ctx,
+                 const char *dn,
+                 const char **_parent_dn)
+{
+    struct ldb_dn *ldb_dn;
+    struct ldb_dn *parent_ldb_dn;
+    const char *p;
+    int ret;
+    TALLOC_CTX *tmp_ctx = NULL;
+
+    tmp_ctx = talloc_new(NULL);
+    if (tmp_ctx == NULL) {
+        ret = ENOMEM;
+        goto done;
+    }
+
+    ldb_dn = ldb_dn_new(tmp_ctx, ldb_ctx, dn);
+    parent_ldb_dn = ldb_dn_get_parent(tmp_ctx, ldb_dn);
+    p = ldb_dn_get_linearized(parent_ldb_dn);
+
+    *_parent_dn = talloc_steal(mem_ctx, p);
+    ret = EOK;
+
+ done:
+    talloc_free(tmp_ctx);
+    return ret;
+}
+
+/*
+ * This function populates the _som_list output parameter by parsing the input
+ * DN into a list of gp_som objects. This function essentially repeatedly
+ * appends the input DN's parent to the SOM List (if the parent starts with
+ * "OU=" or "DC="), until the first "DC=" component is reached.
+ * Example: if input DN is "CN=MyComputer,CN=Computers,OU=Sales,DC=FOO,DC=COM",
+ * then SOM List has 2 SOM entries: {[OU=Sales,DC=FOO,DC=COM], [DC=FOO, DC=COM]}
+ */
+
+static errno_t
+ad_gpo_populate_som_list(TALLOC_CTX *mem_ctx,
+                         struct ldb_context *ldb_ctx,
+                         const char *target_dn,
+                         int *_num_soms,
+                         struct gp_som ***_som_list)
+{
+    TALLOC_CTX *tmp_ctx = NULL;
+    int ret;
+    int rdn_count = 0;
+    int som_idx = 0;
+    struct gp_som **som_list;
+    const char *parent_dn = NULL;
+    const char *tmp_dn = NULL;
+    struct ldb_dn *ldb_target_dn;
+
+    tmp_ctx = talloc_new(NULL);
+    if (tmp_ctx == NULL) {
+        ret = ENOMEM;
+        goto done;
+    }
+
+    ldb_target_dn = ldb_dn_new(tmp_ctx, ldb_ctx, target_dn);
+    rdn_count = ldb_dn_get_comp_num(ldb_target_dn);
+
+    if (rdn_count == 0) {
+        *_som_list = NULL;
+        ret = EOK;
+        goto done;
+    }
+
+    /* assume the worst-case, in which every parent is a SOM */
+    /* include space for Site SOM and NULL: rdn_count + 1 + 1 */
+    som_list = talloc_array(tmp_ctx, struct gp_som *, rdn_count + 1 + 1);
+    if (som_list == NULL) {
+        ret = ENOMEM;
+        goto done;
+    }
+
+    /* first, populate the OU and Domain SOMs */
+    tmp_dn = target_dn;;
+    while ((ad_gpo_parent_dn(tmp_ctx, ldb_ctx, tmp_dn, &parent_dn)) == EOK) {
+
+        if ((strncasecmp(parent_dn, "OU=", strlen("OU=")) == 0) ||
+            (strncasecmp(parent_dn, "DC=", strlen("DC=")) == 0)) {
+
+            som_list[som_idx] = talloc_zero(som_list, struct gp_som);
+            if (som_list[som_idx] == NULL) {
+                ret = ENOMEM;
+                goto done;
+            }
+            som_list[som_idx]->som_dn = talloc_steal(som_list[som_idx],
+                                                     parent_dn);
+            if (som_list[som_idx]->som_dn == NULL) {
+                ret = ENOMEM;
+                goto done;
+            }
+            som_idx++;
+        }
+
+        if (strncasecmp(parent_dn, "DC=", strlen("DC=")) == 0) {
+            break;
+        }
+        tmp_dn = parent_dn;
+    }
+
+    som_list[som_idx] = NULL;
+
+    *_num_soms = som_idx;
+    *_som_list = talloc_steal(mem_ctx, som_list);
+
+    ret = EOK;
+
+ done:
+    talloc_free(tmp_ctx);
+    return ret;
+}
+
+/*
+ * This function populates the _gplink_list output parameter by parsing the
+ * input raw_gplink_value into an array of gp_gplink objects, each consisting of
+ * a GPO DN and bool enforced field.
+ *
+ * The raw_gplink_value is single string consisting of multiple gplink strings.
+ * The raw_gplink_value is in the following format:
+ *  "[GPO_DN_1;GPLinkOptions_1]...[GPO_DN_n;GPLinkOptions_n]"
+ *
+ * Each gplink string consists of a GPO DN and a GPLinkOptions field (which
+ * indicates whether its associated GPO DN is ignored, unenforced, or enforced).
+ * If a GPO DN is flagged as ignored, it is discarded and will not be added to
+ * the _gplink_list. If the allow_enforced_only input is true, AND a GPO DN is
+ * flagged as unenforced, it will also be discarded.
+ *
+ * Example: if raw_gplink_value="[OU=Sales,DC=FOO,DC=COM;0][DC=FOO,DC=COM;2]"
+ *   and allow_enforced_only=FALSE, then the output would consist of following:
+ *    _gplink_list[0]: {GPO DN: "OU=Sales,DC=FOO,DC=COM", enforced: FALSE}
+ *    _gplink_list[1]: {GPO DN: "DC=FOO,DC=COM",          enforced: TRUE}
+ */
+static errno_t
+ad_gpo_populate_gplink_list(TALLOC_CTX *mem_ctx,
+                            const char *som_dn,
+                            char *raw_gplink_value,
+                            struct gp_gplink ***_gplink_list,
+                            bool allow_enforced_only)
+{
+    TALLOC_CTX *tmp_ctx = NULL;
+    char *ptr;
+    char *first;
+    char *last;
+    char *dn;
+    char *gplink_options;
+    const char delim = ']';
+    struct gp_gplink **gplink_list;
+    int i;
+    int ret;
+    uint32_t gplink_number;
+    int gplink_count = 0;
+    int num_enabled = 0;
+
+    if (raw_gplink_value == NULL ||
+        *raw_gplink_value == '\0' ||
+        _gplink_list == NULL) {
+        return EINVAL;
+    }
+
+    DEBUG(SSSDBG_TRACE_ALL, "som_dn: %s\n", som_dn);
+    tmp_ctx = talloc_new(NULL);
+    if (tmp_ctx == NULL) {
+        ret = ENOMEM;
+        goto done;
+    }
+
+    ptr = raw_gplink_value;
+
+    while ((ptr = strchr(ptr, delim))) {
+        ptr++;
+        gplink_count++;
+    }
+
+    if (gplink_count == 0) {
+        ret = EINVAL;
+        goto done;
+    }
+
+    gplink_list = talloc_array(tmp_ctx, struct gp_gplink *, gplink_count + 1);
+    if (gplink_list == NULL) {
+        ret = ENOMEM;
+        goto done;
+    }
+
+    num_enabled = 0;
+    ptr = raw_gplink_value;
+    for (i = 0; i < gplink_count; i++) {
+        first = ptr + 1;
+        last = strchr(first, delim);
+        if (last == NULL) {
+            break;
+        }
+        *last = '\0';
+        last++;
+        dn = first;
+        if ( strncasecmp(dn, "LDAP://", 7)== 0 ) {
+            dn = dn + 7;
+        }
+        gplink_options = strchr(first, ';');
+        if (gplink_options == NULL) {
+            continue;
+        }
+        *gplink_options = '\0';
+        gplink_options++;
+
+        gplink_number = strtouint32(gplink_options, NULL, 10);
+        if (errno != 0) {
+            ret = errno;
+            DEBUG(SSSDBG_OP_FAILURE,
+                  "strtouint32 failed: [%d](%s)\n", ret, sss_strerror(ret));
+            goto done;
+        }
+
+        DEBUG(SSSDBG_TRACE_ALL,
+              "gplink_list[%d]: [%s; %d]\n", num_enabled, dn, gplink_number);
+
+        if ((gplink_number == 1) || (gplink_number ==3)) {
+            /* ignore flag is set */
+            DEBUG(SSSDBG_TRACE_ALL, "ignored gpo skipped\n");
+            ptr = last;
+            continue;
+        }
+
+        if (allow_enforced_only && (gplink_number == 0)) {
+            /* unenforced flag is set; only enforced gpos allowed */
+            DEBUG(SSSDBG_TRACE_ALL, "unenforced gpo skipped\n");
+            ptr = last;
+            continue;
+        }
+
+        gplink_list[num_enabled] = talloc_zero(gplink_list, struct gp_gplink);
+        if (gplink_list[num_enabled] == NULL) {
+            ret = ENOMEM;
+            goto done;
+        }
+        gplink_list[num_enabled]->gpo_dn =
+            talloc_strdup(gplink_list[num_enabled], dn);
+
+        if (gplink_list[num_enabled]->gpo_dn == NULL) {
+            ret = ENOMEM;
+            goto done;
+        }
+
+        if (gplink_number == 0) {
+            gplink_list[num_enabled]->enforced = 0;
+            num_enabled++;
+        } else if (gplink_number == 2) {
+            gplink_list[num_enabled]->enforced = 1;
+            num_enabled++;
+        } else {
+            ret = EINVAL;
+            goto done;
+        }
+
+        ptr = last;
+    }
+    gplink_list[num_enabled] = NULL;
+
+    *_gplink_list = talloc_steal(mem_ctx, gplink_list);
+    ret = EOK;
+
+ done:
+    talloc_free(tmp_ctx);
+    return ret;
+}
+
+/* == ad_gpo_process_som_send/recv implementation ========================== */
+
+struct ad_gpo_process_som_state {
+    struct tevent_context *ev;
+    struct sdap_id_op *sdap_op;
+    struct sdap_options *opts;
+    int timeout;
+    bool allow_enforced_only;
+    char *site_name;
+    char *site_dn;
+    struct gp_som **som_list;
+    int som_index;
+    int num_soms;
+};
+
+static void ad_gpo_site_name_retrieval_done(struct tevent_req *subreq);
+static void ad_gpo_site_dn_retrieval_done(struct tevent_req *subreq);
+static errno_t ad_gpo_get_som_attrs_step(struct tevent_req *req);
+static void ad_gpo_get_som_attrs_done(struct tevent_req *subreq);
+
+
+/*
+ * This function uses the input target_dn and input domain_name to populate
+ * a list of gp_som objects. Each object in this list represents a SOM
+ * associated with the target (such as OU, Domain, and Site).
+ *
+ * The inputs are used to determine the DNs of each SOM associated with the
+ * target. In turn, the SOM object DNs are used to retrieve certain LDAP
+ * attributes of each SOM object, that are parsed into an array of gp_gplink
+ * objects, essentially representing the GPOs that have been linked to each
+ * SOM object. Note that it is perfectly valid for there to be *no* GPOs
+ * linked to a SOM object.
+ */
+struct tevent_req *
+ad_gpo_process_som_send(TALLOC_CTX *mem_ctx,
+                        struct tevent_context *ev,
+                        struct sdap_id_conn_ctx *conn,
+                        struct ldb_context *ldb_ctx,
+                        struct sdap_id_op *sdap_op,
+                        struct sdap_options *opts,
+                        int timeout,
+                        const char *target_dn,
+                        const char *domain_name)
+{
+    struct tevent_req *req;
+    struct tevent_req *subreq;
+    struct ad_gpo_process_som_state *state;
+    errno_t ret;
+
+    req = tevent_req_create(mem_ctx, &state, struct ad_gpo_process_som_state);
+    if (req == NULL) {
+        DEBUG(SSSDBG_CRIT_FAILURE, "tevent_req_create() failed\n");
+        return NULL;
+    }
+
+    state->ev = ev;
+    state->sdap_op = sdap_op;
+    state->opts = opts;
+    state->timeout = timeout;
+    state->som_index = -1;
+    state->allow_enforced_only = 0;
+
+    ret = ad_gpo_populate_som_list(state, ldb_ctx, target_dn,
+                                   &state->num_soms, &state->som_list);
+    if (ret != EOK) {
+        DEBUG(SSSDBG_OP_FAILURE,
+              "Unable to retrieve SOM List : [%d](%s)\n",
+              ret, sss_strerror(ret));
+        ret = ENOENT;
+        goto immediately;
+    }
+
+    if (state->som_list == NULL) {
+        DEBUG(SSSDBG_OP_FAILURE, "target dn must have at least one parent\n");
+        ret = EINVAL;
+        goto immediately;
+    }
+
+    subreq = ad_master_domain_send(state, state->ev, conn,
+                                   state->sdap_op, domain_name);
+
+    if (subreq == NULL) {
+        DEBUG(SSSDBG_OP_FAILURE, "ad_master_domain_send failed.\n");
+        ret = ENOMEM;
+        goto immediately;
+    }
+
+    tevent_req_set_callback(subreq, ad_gpo_site_name_retrieval_done, req);
+
+    ret = EOK;
+
+ immediately:
+
+    if (ret != EOK) {
+        tevent_req_error(req, ret);
+        tevent_req_post(req, ev);
+    }
+
+    return req;
+}
+
+static void
+ad_gpo_site_name_retrieval_done(struct tevent_req *subreq)
+{
+    struct tevent_req *req;
+    struct ad_gpo_process_som_state *state;
+    int ret;
+    char *site;
+    const char *attrs[] = {AD_AT_CONFIG_NC, NULL};
+
+    req = tevent_req_callback_data(subreq, struct tevent_req);
+    state = tevent_req_data(req, struct ad_gpo_process_som_state);
+
+    /* gpo code only cares about the site name */
+    ret = ad_master_domain_recv(subreq, state, NULL, NULL, &site, NULL);
+    talloc_zfree(subreq);
+
+    if (ret != EOK) {
+        DEBUG(SSSDBG_OP_FAILURE, "Cannot retrieve master domain info\n");
+        tevent_req_error(req, ENOENT);
+        return;
+    }
+
+    state->site_name = talloc_asprintf(state, "cn=%s", site);
+    if (state->site_name == NULL) {
+        tevent_req_error(req, ENOMEM);
+        return;
+    }
+
+    /*
+     * note: the configNC attribute is being retrieved here from the rootDSE
+     * entry. In future, since we already make an LDAP query for the rootDSE
+     * entry when LDAP connection is made, this attribute should really be
+     * retrieved at that point (see https://fedorahosted.org/sssd/ticket/2276)
+     */
+    subreq = sdap_get_generic_send(state, state->ev, state->opts,
+                                   sdap_id_op_handle(state->sdap_op),
+                                   "", LDAP_SCOPE_BASE,
+                                   "(objectclass=*)", attrs, NULL, 0,
+                                   state->timeout,
+                                   false);
+
+    if (subreq == NULL) {
+        DEBUG(SSSDBG_OP_FAILURE, "sdap_get_generic_send failed.\n");
+        tevent_req_error(req, ENOMEM);
+        return;
+    }
+
+    tevent_req_set_callback(subreq, ad_gpo_site_dn_retrieval_done, req);
+}
+
+static void
+ad_gpo_site_dn_retrieval_done(struct tevent_req *subreq)
+{
+    struct tevent_req *req;
+    struct ad_gpo_process_som_state *state;
+    int ret;
+    int dp_error;
+    int i = 0;
+    size_t reply_count;
+    struct sysdb_attrs **reply;
+    const char *configNC;
+
+    req = tevent_req_callback_data(subreq, struct tevent_req);
+    state = tevent_req_data(req, struct ad_gpo_process_som_state);
+
+    ret = sdap_get_generic_recv(subreq, state,
+                                &reply_count, &reply);
+    talloc_zfree(subreq);
+    if (ret != EOK) {
+        ret = sdap_id_op_done(state->sdap_op, ret, &dp_error);
+        /* TBD: handle (dp_error == DP_ERR_OFFLINE) case */
+
+        DEBUG(SSSDBG_OP_FAILURE,
+              "Unable to get configNC: [%d](%s)\n", ret, sss_strerror(ret));
+        ret = ENOENT;
+        goto done;
+    }
+
+    /* make sure there is only one non-NULL reply returned */
+
+    if (reply_count < 1) {
+        DEBUG(SSSDBG_OP_FAILURE, "No configNC retrieved\n");
+        ret = ENOENT;
+        goto done;
+    } else if (reply_count > 1) {
+        DEBUG(SSSDBG_OP_FAILURE, "Multiple replies for configNC\n");
+        ret = ERR_INTERNAL;
+        goto done;
+    } else if (reply == NULL) {
+        DEBUG(SSSDBG_OP_FAILURE, "reply_count is 1, but reply is NULL\n");
+        ret = ERR_INTERNAL;
+        goto done;
+    }
+
+    /* reply[0] holds requested attributes of single reply */
+    ret = sysdb_attrs_get_string(reply[0], AD_AT_CONFIG_NC, &configNC);
+    if (ret != EOK) {
+        DEBUG(SSSDBG_OP_FAILURE,
+              "sysdb_attrs_get_string failed: [%d](%s)\n",
+              ret, sss_strerror(ret));
+        goto done;
+    }
+    state->site_dn =
+        talloc_asprintf(state, "%s,cn=Sites,%s", state->site_name, configNC);
+    if (state->site_dn == NULL) {
+        ret = ENOMEM;
+        goto done;
+    }
+
+    /* note that space was allocated for site_dn when allocating som_list */
+    state->som_list[state->num_soms] =
+        talloc_zero(state->som_list, struct gp_som);
+    if (state->som_list[state->num_soms] == NULL) {
+        ret = ENOMEM;
+        goto done;
+    }
+
+    state->som_list[state->num_soms]->som_dn =
+        talloc_steal(state->som_list[state->num_soms], state->site_dn);
+
+    if (state->som_list[state->num_soms]->som_dn == NULL) {
+        ret = ENOMEM;
+        goto done;
+    }
+
+    state->num_soms++;
+    state->som_list[state->num_soms] = NULL;
+
+    i = 0;
+    while (state->som_list[i]) {
+        DEBUG(SSSDBG_TRACE_FUNC, "som_list[%d]->som_dn is %s\n", i,
+              state->som_list[i]->som_dn);
+        i++;
+    }
+
+    ret = ad_gpo_get_som_attrs_step(req);
+
+ done:
+
+    if (ret == EOK) {
+        tevent_req_done(req);
+    } else if (ret != EAGAIN) {
+        tevent_req_error(req, ret);
+    }
+
+}
+static errno_t
+ad_gpo_get_som_attrs_step(struct tevent_req *req)
+{
+    const char *attrs[] = {AD_AT_GPLINK, AD_AT_GPOPTIONS, NULL};
+    struct tevent_req *subreq;
+    struct ad_gpo_process_som_state *state;
+
+    state = tevent_req_data(req, struct ad_gpo_process_som_state);
+
+    state->som_index++;
+    struct gp_som *gp_som = state->som_list[state->som_index];
+
+    /* gp_som is NULL only after all SOMs have been processed */
+    if (gp_som == NULL) return EOK;
+
+    const char *som_dn = gp_som->som_dn;
+    subreq = sdap_get_generic_send(state, state->ev,  state->opts,
+                                   sdap_id_op_handle(state->sdap_op),
+                                   som_dn, LDAP_SCOPE_BASE,
+                                   "(objectclass=*)", attrs, NULL, 0,
+                                   state->timeout,
+                                   false);
+
+    if (subreq == NULL) {
+        DEBUG(SSSDBG_OP_FAILURE, "sdap_get_generic_send failed.\n");
+        return ENOMEM;
+    }
+
+    tevent_req_set_callback(subreq, ad_gpo_get_som_attrs_done, req);
+    return EAGAIN;
+}
+
+static void
+ad_gpo_get_som_attrs_done(struct tevent_req *subreq)
+{
+    struct tevent_req *req;
+    struct ad_gpo_process_som_state *state;
+    int ret;
+    int dp_error;
+    size_t num_results;
+    struct sysdb_attrs **results;
+    struct ldb_message_element *el = NULL;
+    uint8_t *raw_gplink_value;
+    uint8_t *raw_gpoptions_value;
+    uint32_t allow_enforced_only = 0;
+    struct gp_som *gp_som;
+
+    req = tevent_req_callback_data(subreq, struct tevent_req);
+    state = tevent_req_data(req, struct ad_gpo_process_som_state);
+    ret = sdap_get_generic_recv(subreq, state,
+                                &num_results, &results);
+    talloc_zfree(subreq);
+
+    if (ret != EOK) {
+        ret = sdap_id_op_done(state->sdap_op, ret, &dp_error);
+        /* TBD: handle (dp_error == DP_ERR_OFFLINE) case */
+
+        DEBUG(SSSDBG_OP_FAILURE,
+              "Unable to get SOM attributes: [%d](%s)\n",
+              ret, sss_strerror(ret));
+        ret = ENOENT;
+        goto done;
+    }
+    if ((num_results < 1) || (results == NULL)) {
+        DEBUG(SSSDBG_OP_FAILURE, "no attrs found for SOM; try next SOM.\n");
+        ret = ad_gpo_get_som_attrs_step(req);
+        goto done;
+    } else if (num_results > 1) {
+        DEBUG(SSSDBG_OP_FAILURE, "Received multiple replies\n");
+        ret = ERR_INTERNAL;
+        goto done;
+    }
+
+    /* Get the gplink value, if available */
+    ret = sysdb_attrs_get_el(results[0], AD_AT_GPLINK, &el);
+
+    if (ret != EOK && ret != ENOENT) {
+        DEBUG(SSSDBG_OP_FAILURE,
+              "sysdb_attrs_get_el() failed: [%d](%s)\n",
+              ret, sss_strerror(ret));
+        goto done;
+    }
+
+    if ((ret == ENOENT) || (el->num_values == 0)) {
+        DEBUG(SSSDBG_OP_FAILURE, "no attrs found for SOM; try next SOM\n");
+        ret = ad_gpo_get_som_attrs_step(req);
+        goto done;
+    }
+
+    raw_gplink_value = el[0].values[0].data;
+
+    ret = sysdb_attrs_get_el(results[0], AD_AT_GPOPTIONS, &el);
+
+    if (ret != EOK && ret != ENOENT) {
+        DEBUG(SSSDBG_OP_FAILURE, "sysdb_attrs_get_el() failed\n");
+        goto done;
+    }
+
+    if ((ret == ENOENT) || (el->num_values == 0)) {
+        DEBUG(SSSDBG_TRACE_ALL,
+              "gpoptions attr not found or has no value; defaults to 0\n");
+        allow_enforced_only = 0;
+    }  else {
+        raw_gpoptions_value = el[0].values[0].data;
+        allow_enforced_only = strtouint32((char *)raw_gpoptions_value, NULL, 10);
+        if (errno != 0) {
+            ret = errno;
+            DEBUG(SSSDBG_OP_FAILURE,
+                  "strtouint32 failed: [%d](%s)\n", ret, sss_strerror(ret));
+            goto done;
+        }
+    }
+
+    gp_som = state->som_list[state->som_index];
+    ret = ad_gpo_populate_gplink_list(gp_som,
+                                      gp_som->som_dn,
+                                      (char *)raw_gplink_value,
+                                      &gp_som->gplink_list,
+                                      state->allow_enforced_only);
+
+    if (ret != EOK) {
+        DEBUG(SSSDBG_OP_FAILURE,
+              "ad_gpo_populate_gplink_list() failed\n");
+        goto done;
+    }
+
+    if (allow_enforced_only) {
+        state->allow_enforced_only = 1;
+    }
+
+    ret = ad_gpo_get_som_attrs_step(req);
+
+ done:
+
+    if (ret == EOK) {
+        tevent_req_done(req);
+    } else if (ret != EAGAIN) {
+        tevent_req_error(req, ret);
+    }
+}
+
+int
+ad_gpo_process_som_recv(struct tevent_req *req,
+                        TALLOC_CTX *mem_ctx,
+                        struct gp_som ***som_list)
+{
+
+    struct ad_gpo_process_som_state *state =
+        tevent_req_data(req, struct ad_gpo_process_som_state);
+
+    TEVENT_REQ_RETURN_ON_ERROR(req);
+    *som_list = talloc_steal(mem_ctx, state->som_list);
+    return EOK;
+}
+
+/* == ad_gpo_process_gpo_send/recv helpers ================================= */
+
+/*
+ * This function examines the gp_gplink objects in each gp_som object specified
+ * in the input som_list, and populates the _candidate_gpos output parameter's
+ * gpo_dn fields with prioritized list of GPO DNs. Prioritization ensures that:
+ * - GPOs linked to an OU will be applied after GPOs linked to a Domain,
+ *   which will be applied after GPOs linked to a Site.
+ * - multiple GPOs linked to a single SOM are applied in their link order
+ *   (i.e. 1st GPO linked to SOM is applied after 2nd GPO linked to SOM, etc).
+ * - enforced GPOs are applied after unenforced GPOs.
+ *
+ * As such, the _candidate_gpos output's dn fields looks like (in link order):
+ * [unenforced {Site, Domain, OU}; enforced {Site, Domain, OU}]
+ *
+ * Note that in the case of conflicting policy settings, GPOs appearing later
+ * in the list will trump GPOs appearing earlier in the list.
+ */
+static errno_t
+ad_gpo_populate_candidate_gpos(TALLOC_CTX *mem_ctx,
+                               struct gp_som **som_list,
+                               struct gp_gpo ***_candidate_gpos,
+                               int *_num_candidate_gpos)
+{
+
+    TALLOC_CTX *tmp_ctx = NULL;
+    struct gp_som *gp_som = NULL;
+    struct gp_gplink *gp_gplink = NULL;
+    struct gp_gpo **candidate_gpos = NULL;
+    int num_candidate_gpos = 0;
+    const char **enforced_gpo_dns = NULL;
+    const char **unenforced_gpo_dns = NULL;
+    int gpo_dn_idx = 0;
+    int num_enforced = 0;
+    int enforced_idx = 0;
+    int num_unenforced = 0;
+    int unenforced_idx = 0;
+    int i = 0;
+    int j = 0;
+    int ret;
+
+    tmp_ctx = talloc_new(NULL);
+    if (tmp_ctx == NULL) {
+        ret = ENOMEM;
+        goto done;
+    }
+
+    while (som_list[i]) {
+        gp_som = som_list[i];
+        j = 0;
+        while (gp_som && gp_som->gplink_list && gp_som->gplink_list[j]) {
+            gp_gplink = gp_som->gplink_list[j];
+            if (gp_gplink == NULL) {
+                DEBUG(SSSDBG_OP_FAILURE, "unexpected null gp_gplink\n");
+                ret = EINVAL;
+                goto done;
+            }
+            if (gp_gplink->enforced) {
+                num_enforced++;
+            } else {
+                num_unenforced++;
+            }
+            j++;
+        }
+        i++;
+    }
+
+    num_candidate_gpos = num_enforced + num_unenforced;
+
+    if (num_candidate_gpos == 0) {
+        *_candidate_gpos = NULL;
+        *_num_candidate_gpos = 0;
+        ret = EOK;
+        goto done;
+    }
+
+    enforced_gpo_dns = talloc_array(tmp_ctx, const char *, num_enforced + 1);
+    if (enforced_gpo_dns == NULL) {
+        ret = ENOMEM;
+        goto done;
+    }
+
+    unenforced_gpo_dns = talloc_array(tmp_ctx, const char *, num_unenforced + 1);
+    if (unenforced_gpo_dns == NULL) {
+        ret = ENOMEM;
+        goto done;
+    }
+
+    i = 0;
+    while (som_list[i]) {
+        gp_som = som_list[i];
+        j = 0;
+        while (gp_som && gp_som->gplink_list && gp_som->gplink_list[j]) {
+            gp_gplink = gp_som->gplink_list[j];
+            if (gp_gplink == NULL) {
+                DEBUG(SSSDBG_OP_FAILURE, "unexpected null gp_gplink\n");
+                ret = EINVAL;
+                goto done;
+            }
+
+            if (gp_gplink->enforced) {
+                enforced_gpo_dns[enforced_idx] =
+                    talloc_steal(enforced_gpo_dns, gp_gplink->gpo_dn);
+                if (enforced_gpo_dns[enforced_idx] == NULL) {
+                    ret = ENOMEM;
+                    goto done;
+                }
+                enforced_idx++;
+            } else {
+
+                unenforced_gpo_dns[unenforced_idx] =
+                    talloc_steal(unenforced_gpo_dns, gp_gplink->gpo_dn);
+
+                if (unenforced_gpo_dns[unenforced_idx] == NULL) {
+                    ret = ENOMEM;
+                    goto done;
+                }
+                unenforced_idx++;
+            }
+            j++;
+        }
+        i++;
+    }
+    enforced_gpo_dns[num_enforced] = NULL;
+    unenforced_gpo_dns[num_unenforced] = NULL;
+
+    candidate_gpos = talloc_array(tmp_ctx,
+                                  struct gp_gpo *,
+                                  num_candidate_gpos + 1);
+
+    if (candidate_gpos == NULL) {
+        ret = ENOMEM;
+        goto done;
+    }
+
+    gpo_dn_idx = 0;
+    for (i = num_unenforced - 1; i >= 0; i--) {
+        candidate_gpos[gpo_dn_idx] = talloc_zero(candidate_gpos, struct gp_gpo);
+        if (candidate_gpos[gpo_dn_idx] == NULL) {
+            ret = ENOMEM;
+            goto done;
+        }
+        candidate_gpos[gpo_dn_idx]->gpo_dn =
+            talloc_steal(candidate_gpos[gpo_dn_idx], unenforced_gpo_dns[i]);
+
+        if (candidate_gpos[gpo_dn_idx]->gpo_dn == NULL) {
+            ret = ENOMEM;
+            goto done;
+        }
+        DEBUG(SSSDBG_TRACE_FUNC,
+              "candidate_gpos[%d]->gpo_dn: %s\n",
+              gpo_dn_idx, candidate_gpos[gpo_dn_idx]->gpo_dn);
+        gpo_dn_idx++;
+    }
+
+    for (i = 0; i < num_enforced; i++) {
+
+        candidate_gpos[gpo_dn_idx] = talloc_zero(candidate_gpos, struct gp_gpo);
+        if (candidate_gpos[gpo_dn_idx] == NULL) {
+            ret = ENOMEM;
+            goto done;
+        }
+
+        candidate_gpos[gpo_dn_idx]->gpo_dn =
+            talloc_steal(candidate_gpos[gpo_dn_idx], enforced_gpo_dns[i]);
+        if (candidate_gpos[gpo_dn_idx]->gpo_dn == NULL) {
+            ret = ENOMEM;
+            goto done;
+        }
+
+        DEBUG(SSSDBG_TRACE_FUNC,
+              "candidate_gpos[%d]->gpo_dn: %s\n",
+              gpo_dn_idx, candidate_gpos[gpo_dn_idx]->gpo_dn);
+        gpo_dn_idx++;
+    }
+
+    candidate_gpos[gpo_dn_idx] = NULL;
+
+    *_candidate_gpos = talloc_steal(mem_ctx, candidate_gpos);
+    *_num_candidate_gpos = num_candidate_gpos;
+
+    ret = EOK;
+
+ done:
+    talloc_free(tmp_ctx);
+    return ret;
+}
+
+/*
+ * This function converts the input_path to an smb uri, which is used to
+ * populate the _converted_path output parameter. The conversion consists of:
+ * - prepending "smb:"
+ * - replacing each forward slash ('\') with a back slash character ('/')
+ */
+static errno_t
+ad_gpo_convert_to_smb_uri(TALLOC_CTX *mem_ctx,
+                          char *input_path,
+                          const char **_converted_path)
+{
+    char *ptr;
+    const char delim = '\\';
+    int ret;
+    int num_seps = 0;
+
+    DEBUG(SSSDBG_TRACE_ALL, "input_path: %s\n", input_path);
+
+    if (input_path == NULL ||
+        *input_path == '\0' ||
+        _converted_path == NULL) {
+        ret = EINVAL;
+        goto done;
+    }
+
+    ptr = input_path;
+    while ((ptr = strchr(ptr, delim))) {
+        *ptr = '/';
+        ptr++;
+        num_seps++;
+    }
+
+    if (num_seps == 0) {
+        ret = EINVAL;
+        goto done;
+    }
+
+    *_converted_path = talloc_asprintf(mem_ctx, "smb:%s", input_path);
+    ret = EOK;
+
+ done:
+    return ret;
+}
+
+/*
+ * This function populates the _cse_guid_list output parameter by parsing the
+ * input raw_machine_ext_names_value into an array of cse_guid strings.
+ *
+ * The raw_machine_ext_names_value is a single string in the following format:
+ * "[{cse_guid_1}{tool_guid1}]...[{cse_guid_n}{tool_guid_n}]"
+ */
+static errno_t
+ad_gpo_parse_machine_ext_names(TALLOC_CTX *mem_ctx,
+                               char *raw_machine_ext_names_value,
+                               const char ***_gpo_cse_guids,
+                               int *_num_gpo_cse_guids)
+{
+    TALLOC_CTX *tmp_ctx = NULL;
+    char *ptr;
+    char *first;
+    char *last;
+    char *cse_guid;
+    char *tool_guid;
+    const char delim = ']';
+    const char **gpo_cse_guids;
+    int i;
+    int ret;
+    int num_gpo_cse_guids = 0;
+
+    if (raw_machine_ext_names_value == NULL ||
+        *raw_machine_ext_names_value == '\0' ||
+        _gpo_cse_guids == NULL) {
+        return EINVAL;
+    }
+
+    tmp_ctx = talloc_new(NULL);
+    if (tmp_ctx == NULL) {
+        ret = ENOMEM;
+        goto done;
+    }
+
+    ptr = raw_machine_ext_names_value;
+    while ((ptr = strchr(ptr, delim))) {
+        ptr++;
+        num_gpo_cse_guids++;
+    }
+
+    if (num_gpo_cse_guids == 0) {
+        ret = EINVAL;
+        goto done;
+    }
+
+    gpo_cse_guids = talloc_array(tmp_ctx, const char *, num_gpo_cse_guids + 1);
+    if (gpo_cse_guids == NULL) {
+        ret = ENOMEM;
+        goto done;
+    }
+
+    ptr = raw_machine_ext_names_value;
+    for (i = 0; i < num_gpo_cse_guids; i++) {
+        first = ptr + 1;
+        last = strchr(first, delim);
+        if (last == NULL) {
+            break;
+        }
+        *last = '\0';
+        last++;
+        cse_guid = first;
+        first ++;
+        tool_guid = strchr(first, '{');
+        if (tool_guid == NULL) {
+            break;
+        }
+        *tool_guid = '\0';
+        gpo_cse_guids[i] = talloc_strdup(gpo_cse_guids, cse_guid);
+        ptr = last;
+    }
+    gpo_cse_guids[i] = NULL;
+
+    DEBUG(SSSDBG_TRACE_ALL, "num_gpo_cse_guids: %d\n", num_gpo_cse_guids);
+
+    for (i = 0; i < num_gpo_cse_guids; i++) {
+        DEBUG(SSSDBG_TRACE_ALL,
+              "gpo_cse_guids[%d] is %s\n", i, gpo_cse_guids[i]);
+    }
+
+    *_gpo_cse_guids = talloc_steal(mem_ctx, gpo_cse_guids);
+    *_num_gpo_cse_guids = num_gpo_cse_guids;
+    ret = EOK;
+
+ done:
+    talloc_free(tmp_ctx);
+    return ret;
+}
+
+enum ndr_err_code
+ndr_pull_security_descriptor(struct ndr_pull *ndr, int ndr_flags,
+                             struct security_descriptor *r);
+
+/*
+ * This function parses the input data blob and assigns the resulting
+ * security_descriptor object to the _gpo_sd output parameter.
+ */
+static errno_t ad_gpo_parse_sd(TALLOC_CTX *mem_ctx,
+                               uint8_t *data,
+                               size_t length,
+                               struct security_descriptor **_gpo_sd)
+{
+
+    struct ndr_pull *ndr_pull = NULL;
+    struct security_descriptor sd;
+    DATA_BLOB blob;
+
+    blob.data = data;
+    blob.length = length;
+
+    ndr_pull = ndr_pull_init_blob(&blob, mem_ctx);
+    if (ndr_pull == NULL) {
+        DEBUG(SSSDBG_OP_FAILURE, "ndr_pull_init_blob() failed.\n");
+        return EINVAL;
+    }
+
+    ndr_pull_security_descriptor(ndr_pull, NDR_SCALARS|NDR_BUFFERS, &sd);
+
+    *_gpo_sd = talloc_memdup(mem_ctx, &sd, sizeof(struct security_descriptor));
+
+    return EOK;
+}
+
+/* == ad_gpo_process_gpo_send/recv implementation ========================== */
+
+struct ad_gpo_process_gpo_state {
+    struct tevent_context *ev;
+    struct sdap_id_op *sdap_op;
+    struct sdap_options *opts;
+    int timeout;
+    struct gp_gpo **candidate_gpos;
+    int num_candidate_gpos;
+    int gpo_index;
+};
+
+static errno_t ad_gpo_get_gpo_attrs_step(struct tevent_req *req);
+static void ad_gpo_get_gpo_attrs_done(struct tevent_req *subreq);
+
+/*
+ * This function uses the input som_list to populate a prioritized list of
+ * gp_gpo objects, prioritized based on SOM type, link order, and whether the
+ * GPO is "enforced". This list represents the initial set of candidate GPOs
+ * that might be applicable to the target. This list can not be expanded, but
+ * it might be reduced based on subsequent filtering steps. The GPO object DNs
+ * are used to retrieve certain LDAP attributes of each GPO object, that are
+ * parsed into the various fields of the gp_gpo object.
+ */
+struct tevent_req *
+ad_gpo_process_gpo_send(TALLOC_CTX *mem_ctx,
+                        struct tevent_context *ev,
+                        struct sdap_id_op *sdap_op,
+                        struct sdap_options *opts,
+                        int timeout,
+                        struct gp_som **som_list)
+{
+    struct tevent_req *req;
+    struct ad_gpo_process_gpo_state *state;
+    errno_t ret;
+
+    req = tevent_req_create(mem_ctx, &state, struct ad_gpo_process_gpo_state);
+    if (req == NULL) {
+        DEBUG(SSSDBG_CRIT_FAILURE, "tevent_req_create() failed\n");
+        return NULL;
+    }
+
+    state->ev = ev;
+    state->sdap_op = sdap_op;
+    state->opts = opts;
+    state->timeout = timeout;
+    state->gpo_index = -1;
+    state->candidate_gpos = NULL;
+    state->num_candidate_gpos = 0;
+
+    ret = ad_gpo_populate_candidate_gpos(state,
+                                         som_list,
+                                         &state->candidate_gpos,
+                                         &state->num_candidate_gpos);
+
+    if (ret != EOK) {
+        DEBUG(SSSDBG_OP_FAILURE,
+              "Unable to retrieve GPO List: [%d](%s)\n",
+              ret, sss_strerror(ret));
+        ret = ENOENT;
+        goto immediately;
+    }
+
+    if (state->candidate_gpos == NULL) {
+        DEBUG(SSSDBG_OP_FAILURE, "no gpos found\n");
+        ret = ENOENT;
+        goto immediately;
+    }
+
+    ret = ad_gpo_get_gpo_attrs_step(req);
+
+immediately:
+
+    if (ret == EOK) {
+        tevent_req_done(req);
+        tevent_req_post(req, ev);
+    } else if (ret != EAGAIN) {
+        tevent_req_error(req, ret);
+        tevent_req_post(req, ev);
+    }
+
+    return req;
+}
+
+static errno_t
+ad_gpo_get_gpo_attrs_step(struct tevent_req *req)
+{
+    const char *attrs[] = {AD_AT_NT_SEC_DESC, AD_AT_CN, AD_AT_DISPLAY_NAME,
+                           AD_AT_FILE_SYS_PATH, AD_AT_VERSION_NUMBER,
+                           AD_AT_MACHINE_EXT_NAMES, AD_AT_FUNC_VERSION,
+                           AD_AT_FLAGS, NULL};
+    struct tevent_req *subreq;
+    struct ad_gpo_process_gpo_state *state;
+
+    state = tevent_req_data(req, struct ad_gpo_process_gpo_state);
+
+    state->gpo_index++;
+    struct gp_gpo *gp_gpo = state->candidate_gpos[state->gpo_index];
+
+    /* gp_gpo is NULL only after all GPOs have been processed */
+    if (gp_gpo == NULL) return EOK;
+
+    const char *gpo_dn = gp_gpo->gpo_dn;
+
+    subreq = sdap_sd_search_send(state, state->ev,
+                                 state->opts, sdap_id_op_handle(state->sdap_op),
+                                 gpo_dn, SECINFO_DACL, attrs, state->timeout);
+
+    if (subreq == NULL) {
+        DEBUG(SSSDBG_OP_FAILURE, "sdap_get_generic_send failed.\n");
+        return ENOMEM;
+    }
+
+    tevent_req_set_callback(subreq, ad_gpo_get_gpo_attrs_done, req);
+    return EAGAIN;
+}
+
+static void
+ad_gpo_get_gpo_attrs_done(struct tevent_req *subreq)
+{
+    struct tevent_req *req;
+    struct ad_gpo_process_gpo_state *state;
+    int ret;
+    int dp_error;
+    size_t num_results;
+    struct sysdb_attrs **results;
+    struct ldb_message_element *el = NULL;
+    const char *gpo_guid = NULL;
+    const char *smb_uri = NULL;
+    const char *gpo_display_name = NULL;
+    const char *raw_file_sys_path = NULL;
+    char *file_sys_path = NULL;
+    uint8_t *raw_machine_ext_names = NULL;
+
+    req = tevent_req_callback_data(subreq, struct tevent_req);
+    state = tevent_req_data(req, struct ad_gpo_process_gpo_state);
+
+    ret = sdap_sd_search_recv(subreq, state, &num_results, &results);
+    talloc_zfree(subreq);
+
+    if (ret != EOK) {
+        ret = sdap_id_op_done(state->sdap_op, ret, &dp_error);
+        /* TBD: handle (dp_error == DP_ERR_OFFLINE) case */
+
+        DEBUG(SSSDBG_OP_FAILURE,
+              "Unable to get GPO attributes: [%d](%s)\n",
+              ret, sss_strerror(ret));
+        ret = ENOENT;
+        goto done;
+    }
+
+    if ((num_results < 1) || (results == NULL)) {
+        DEBUG(SSSDBG_OP_FAILURE, "no attrs found for GPO; try next GPO.\n");
+        ret = ad_gpo_get_gpo_attrs_step(req);
+        goto done;
+    }
+    else if (num_results > 1) {
+        DEBUG(SSSDBG_OP_FAILURE, "Received multiple replies\n");
+        ret = ERR_INTERNAL;
+        goto done;
+    }
+
+    struct gp_gpo *gp_gpo = state->candidate_gpos[state->gpo_index];
+
+    /* retrieve AD_AT_CN */
+    ret = sysdb_attrs_get_string(results[0], AD_AT_CN, &gpo_guid);
+    if (ret != EOK) {
+        DEBUG(SSSDBG_OP_FAILURE,
+              "sysdb_attrs_get_string failed: [%d](%s)\n",
+              ret, sss_strerror(ret));
+        goto done;
+    }
+
+    gp_gpo->gpo_guid = talloc_steal(gp_gpo, gpo_guid);
+    if (gp_gpo->gpo_guid == NULL) {
+        ret = ENOMEM;
+        goto done;
+    }
+
+    DEBUG(SSSDBG_TRACE_ALL, "populating attrs for gpo_guid: %s\n",
+          gp_gpo->gpo_guid);
+
+    /* retrieve AD_AT_DISPLAY_NAME */
+    ret = sysdb_attrs_get_string(results[0], AD_AT_DISPLAY_NAME,
+                                 &gpo_display_name);
+    if (ret != EOK) {
+        DEBUG(SSSDBG_OP_FAILURE,
+              "sysdb_attrs_get_string failed: [%d](%s)\n",
+              ret, sss_strerror(ret));
+        goto done;
+    }
+
+    gp_gpo->gpo_display_name = talloc_steal(gp_gpo, gpo_display_name);
+    if (gp_gpo->gpo_display_name == NULL) {
+        ret = ENOMEM;
+        goto done;
+    }
+
+    DEBUG(SSSDBG_TRACE_ALL, "gpo_display_name: %s\n",
+                            gp_gpo->gpo_display_name);
+
+    /* retrieve AD_AT_FILE_SYS_PATH */
+    ret = sysdb_attrs_get_string(results[0],
+                                 AD_AT_FILE_SYS_PATH,
+                                 &raw_file_sys_path);
+
+    if (ret != EOK) {
+        DEBUG(SSSDBG_OP_FAILURE,
+              "sysdb_attrs_get_string failed: [%d](%s)\n",
+              ret, sss_strerror(ret));
+        goto done;
+    }
+
+    file_sys_path = talloc_strdup(gp_gpo, raw_file_sys_path);
+    ad_gpo_convert_to_smb_uri(state, file_sys_path, &smb_uri);
+
+    gp_gpo->gpo_file_sys_path = talloc_asprintf(gp_gpo, "%s/Machine",
+                                                smb_uri);
+    if (gp_gpo->gpo_file_sys_path == NULL) {
+        ret = ENOMEM;
+        goto done;
+    }
+
+    DEBUG(SSSDBG_TRACE_FUNC, "gpo_file_sys_path: %s\n",
+          gp_gpo->gpo_file_sys_path);
+
+    /* retrieve AD_AT_VERSION_NUMBER */
+    ret = sysdb_attrs_get_uint32_t(results[0], AD_AT_VERSION_NUMBER,
+                                   &gp_gpo->gpo_container_version);
+    if (ret != EOK) {
+        DEBUG(SSSDBG_OP_FAILURE,
+              "sysdb_attrs_get_uint32_t failed: [%d](%s)\n",
+              ret, sss_strerror(ret));
+        goto done;
+    }
+
+    DEBUG(SSSDBG_TRACE_ALL, "gpo_container_version: %d\n",
+                            gp_gpo->gpo_container_version);
+
+    /* retrieve AD_AT_MACHINE_EXT_NAMES */
+    ret = sysdb_attrs_get_el(results[0], AD_AT_MACHINE_EXT_NAMES, &el);
+    if (ret != EOK && ret != ENOENT) {
+        DEBUG(SSSDBG_OP_FAILURE, "sysdb_attrs_get_el() failed\n");
+        goto done;
+    }
+    if ((ret == ENOENT) || (el->num_values == 0)) {
+        DEBUG(SSSDBG_OP_FAILURE,
+              "machine_ext_names not found or has no value\n");
+        ret = ENOENT;
+        goto done;
+    }
+
+    raw_machine_ext_names = el[0].values[0].data;
+
+    ret = ad_gpo_parse_machine_ext_names(gp_gpo,
+                                         (char *)raw_machine_ext_names,
+                                         &gp_gpo->gpo_cse_guids,
+                                         &gp_gpo->num_gpo_cse_guids);
+    if (ret != EOK) {
+        DEBUG(SSSDBG_OP_FAILURE,
+              "ad_gpo_parse_machine_ext_names() failed\n");
+        goto done;
+    }
+
+    /* retrieve AD_AT_FUNC_VERSION */
+    ret = sysdb_attrs_get_int32_t(results[0], AD_AT_FUNC_VERSION,
+                                  &gp_gpo->gpo_func_version);
+    if (ret != EOK) {
+        DEBUG(SSSDBG_OP_FAILURE,
+              "sysdb_attrs_get_int32_t failed: [%d](%s)\n",
+              ret, sss_strerror(ret));
+        goto done;
+    }
+
+    DEBUG(SSSDBG_TRACE_ALL, "gpo_func_version: %d\n",
+                            gp_gpo->gpo_func_version);
+
+    /* retrieve AD_AT_FLAGS */
+    ret = sysdb_attrs_get_int32_t(results[0], AD_AT_FLAGS,
+                                  &gp_gpo->gpo_flags);
+    if (ret != EOK) {
+        DEBUG(SSSDBG_OP_FAILURE,
+              "sysdb_attrs_get_int32_t failed: [%d](%s)\n",
+              ret, sss_strerror(ret));
+        goto done;
+    }
+
+    DEBUG(SSSDBG_TRACE_ALL, "gpo_flags: %d\n", gp_gpo->gpo_flags);
+
+    /* retrieve AD_AT_NT_SEC_DESC */
+    ret = sysdb_attrs_get_el(results[0], AD_AT_NT_SEC_DESC, &el);
+    if (ret != EOK && ret != ENOENT) {
+        DEBUG(SSSDBG_OP_FAILURE, "sysdb_attrs_get_el() failed\n");
+        goto done;
+    }
+    if ((ret == ENOENT) || (el->num_values == 0)) {
+        DEBUG(SSSDBG_OP_FAILURE,
+              "nt_sec_desc attribute not found or has no value\n");
+        ret = ENOENT;
+        goto done;
+    }
+
+    ret = ad_gpo_parse_sd(gp_gpo, el[0].values[0].data, el[0].values[0].length,
+                          &gp_gpo->gpo_sd);
+    if (ret != EOK) {
+        DEBUG(SSSDBG_OP_FAILURE, "ad_gpo_parse_sd() failed\n");
+        goto done;
+    }
+
+    ret = ad_gpo_get_gpo_attrs_step(req);
+
+ done:
+
+    if (ret == EOK) {
+        tevent_req_done(req);
+    } else if (ret != EAGAIN) {
+        tevent_req_error(req, ret);
+    }
+}
+
+int
+ad_gpo_process_gpo_recv(struct tevent_req *req,
+                        TALLOC_CTX *mem_ctx,
+                        struct gp_gpo ***candidate_gpos,
+                        int *num_candidate_gpos)
+{
+    struct ad_gpo_process_gpo_state *state =
+        tevent_req_data(req, struct ad_gpo_process_gpo_state);
+
+    TEVENT_REQ_RETURN_ON_ERROR(req);
+
+    *candidate_gpos = talloc_steal(mem_ctx, state->candidate_gpos);
+    *num_candidate_gpos = state->num_candidate_gpos;
+    return EOK;
+}