path: root/src/providers/simple/simple_access_check.c

/*
   SSSD

   Simple access control

   Copyright (C) Sumit Bose <sbose@redhat.com> 2010

   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/>.
*/

#include "providers/dp_backend.h"
#include "providers/simple/simple_access.h"
#include "util/sss_utf8.h"
#include "db/sysdb.h"

static bool
is_posix(const struct ldb_message *group)
{
    const char *val;

    val = ldb_msg_find_attr_as_string(group, SYSDB_POSIX, NULL);
    if (!val || /* Groups are posix by default */
        strcasecmp(val, "TRUE") == 0) {
        return true;
    }

    return false;
}

/* Returns EOK if the result is definitive, EAGAIN if only partial result
 */
static errno_t
simple_check_users(struct simple_ctx *ctx, const char *username,
                   bool *access_granted)
{
    int i;
    bool cs = ctx->domain->case_sensitive;

    /* First, check whether the user is in the allowed users list */
    if (ctx->allow_users != NULL) {
        for(i = 0; ctx->allow_users[i] != NULL; i++) {
            if (sss_string_equal(cs, username, ctx->allow_users[i])) {
                DEBUG(SSSDBG_TRACE_LIBS,
                      ("User [%s] found in allow list, access granted.\n",
                      username));

                /* Do not return immediately on explicit allow
                 * We need to make sure none of the user's groups
                 * are denied.
                 */
                *access_granted = true;
            }
        }
    } else if (!ctx->allow_groups) {
        /* If neither allow rule is in place, we'll assume allowed
         * unless a deny rule disables us below.
         */
        DEBUG(SSSDBG_TRACE_LIBS,
              ("No allow rule, assumuing allow unless explicitly denied\n"));
        *access_granted = true;
    }

    /* Next check whether this user has been specifically denied */
    if (ctx->deny_users != NULL) {
        for(i = 0; ctx->deny_users[i] != NULL; i++) {
            if (sss_string_equal(cs, username, ctx->deny_users[i])) {
                DEBUG(SSSDBG_TRACE_LIBS,
                      ("User [%s] found in deny list, access denied.\n",
                      username));

                /* Return immediately on explicit denial */
                *access_granted = false;
                return EOK;
            }
        }
    }

    return EAGAIN;
}

static errno_t
simple_check_groups(struct simple_ctx *ctx, const char *username,
                    const char **group_names, bool *access_granted)
{
    bool matched;
    int i, j;
    bool cs = ctx->domain->case_sensitive;

    /* Now process allow and deny group rules
     * If access was already granted above, we'll skip
     * this redundant rule check
     */
    if (ctx->allow_groups && !*access_granted) {
        matched = false;
        for (i = 0; ctx->allow_groups[i]; i++) {
            for(j = 0; group_names[j]; j++) {
                if (sss_string_equal(cs, group_names[j], ctx->allow_groups[i])) {
                    matched = true;
                    break;
                }
            }

            /* If any group has matched, we can skip out on the
             * processing early
             */
            if (matched) {
                DEBUG(SSSDBG_TRACE_LIBS,
                      ("Group [%s] found in allow list, access granted.\n",
                      group_names[j]));
                *access_granted = true;
                break;
            }
        }
    }

    /* Finally, process the deny group rules */
    if (ctx->deny_groups) {
        matched = false;
        for (i = 0; ctx->deny_groups[i]; i++) {
            for(j = 0; group_names[j]; j++) {
                if (sss_string_equal(cs, group_names[j], ctx->deny_groups[i])) {
                    matched = true;
                    break;
                }
            }

            /* If any group has matched, we can skip out on the
             * processing early
             */
            if (matched) {
                DEBUG(SSSDBG_TRACE_LIBS,
                      ("Group [%s] found in deny list, access denied.\n",
                      group_names[j]));
                *access_granted = false;
                break;
            }
        }
    }

    return EOK;
}

struct simple_resolve_group_state {
    gid_t gid;
    struct simple_ctx *ctx;

    const char *name;
};

static errno_t
simple_resolve_group_check(struct simple_resolve_group_state *state);
static void simple_resolve_group_done(struct tevent_req *subreq);

static struct tevent_req *
simple_resolve_group_send(TALLOC_CTX *mem_ctx,
                          struct tevent_context *ev,
                          struct simple_ctx *ctx,
                          gid_t gid)
{
    errno_t ret;
    struct tevent_req *req;
    struct tevent_req *subreq;
    struct simple_resolve_group_state *state;
    struct be_acct_req *ar;

    req = tevent_req_create(mem_ctx, &state,
                            struct simple_resolve_group_state);
    if (!req) return NULL;

    state->gid = gid;
    state->ctx = ctx;

    /* First check if the group was updated already. If it was (maybe its
     * parent was updated first), then just shortcut */
    ret = simple_resolve_group_check(state);
    if (ret == EOK) {
        DEBUG(SSSDBG_TRACE_LIBS, ("Group already updated\n"));
        ret = EOK;
        goto done;
    } else if (ret != EAGAIN) {
        DEBUG(SSSDBG_OP_FAILURE,
              ("Cannot check if group was already updated\n"));
        goto done;
    }
    /* EAGAIN - still needs update */

    ar = talloc(state, struct be_acct_req);
    if (!ar) {
        ret = ENOMEM;
        goto done;
    }

    ar->entry_type = BE_REQ_GROUP;
    ar->attr_type = BE_ATTR_CORE;
    ar->filter_type = BE_FILTER_IDNUM;
    ar->filter_value = talloc_asprintf(ar, "%llu", (unsigned long long) gid);
    ar->domain = talloc_strdup(ar, ctx->domain->name);
    if (!ar->domain || !ar->filter_value) {
        ret = ENOMEM;
        goto done;
    }

    subreq = be_get_account_info_send(state, ev, NULL, ctx->be_ctx, ar);
    if (!subreq) {
        ret = ENOMEM;
        goto done;
    }
    tevent_req_set_callback(subreq, simple_resolve_group_done, req);

    return req;

done:
    if (ret == EOK) {
        tevent_req_done(req);
    } else {
        tevent_req_error(req, ret);
    }
    tevent_req_post(req, ev);
    return req;
}

static errno_t
simple_resolve_group_check(struct simple_resolve_group_state *state)
{
    errno_t ret;
    struct ldb_message *group;
    const char *group_attrs[] = { SYSDB_NAME, SYSDB_POSIX,
                                  SYSDB_GIDNUM, NULL };

    /* Check the cache by GID again and fetch the name */
    ret = sysdb_search_group_by_gid(state, state->ctx->domain->sysdb,
                                    state->gid, group_attrs, &group);
    if (ret != EOK) {
        DEBUG(SSSDBG_OP_FAILURE,
               ("Could not look up group by gid [%lu]: [%d][%s]\n",
               state->gid, ret, strerror(ret)));
        return ret;
    }

    state->name = ldb_msg_find_attr_as_string(group, SYSDB_NAME, NULL);
    if (!state->name) {
        DEBUG(SSSDBG_OP_FAILURE, ("No group name\n"));
        return ENOENT;
    }

    if (is_posix(group) == false) {
        DEBUG(SSSDBG_TRACE_LIBS,
              ("The group is still non-POSIX\n"));
        return EAGAIN;
    }

    DEBUG(SSSDBG_TRACE_LIBS, ("Got POSIX group\n"));
    return EOK;
}

static void simple_resolve_group_done(struct tevent_req *subreq)
{
    struct tevent_req *req;
    struct simple_resolve_group_state *state;
    int err_maj;
    int err_min;
    errno_t ret;
    const char *err_msg;

    req = tevent_req_callback_data(subreq, struct tevent_req);
    state = tevent_req_data(req, struct simple_resolve_group_state);

    ret = be_get_account_info_recv(subreq, state,
                                   &err_maj, &err_min, &err_msg);
    talloc_zfree(subreq);
    if (ret) {
        DEBUG(SSSDBG_OP_FAILURE, ("be_get_account_info_recv failed\n"));
        tevent_req_error(req, ret);
        return;
    }

    if (err_maj) {
        DEBUG(SSSDBG_MINOR_FAILURE,
              ("Cannot refresh data from DP: %u,%u: %s\n",
              err_maj, err_min, err_msg));
        tevent_req_error(req, EIO);
        return;
    }

    /* Check the cache by GID again and fetch the name */
    ret = simple_resolve_group_check(state);
    if (ret != EOK) {
        DEBUG(SSSDBG_OP_FAILURE, ("Refresh failed\n"));
        tevent_req_error(req, ret);
        return;
    }

    tevent_req_done(req);
}

static errno_t
simple_resolve_group_recv(struct tevent_req *req,
                          TALLOC_CTX *mem_ctx,
                          const char **name)
{
    struct simple_resolve_group_state *state;

    state = tevent_req_data(req, struct simple_resolve_group_state);

    TEVENT_REQ_RETURN_ON_ERROR(req);

    *name = talloc_strdup(mem_ctx, state->name);
    return EOK;
}

struct simple_check_groups_state {
    struct tevent_context *ev;
    struct simple_ctx *ctx;

    gid_t *lookup_gids;
    size_t num_gids;
    size_t giter;

    const char **group_names;
    size_t num_names;
};

static void simple_check_get_groups_next(struct tevent_req *subreq);

static errno_t
simple_check_get_groups_primary(struct simple_check_groups_state *state,
                                gid_t gid);
static errno_t
simple_check_process_group(struct simple_check_groups_state *state,
                           struct ldb_message *group);

static struct tevent_req *
simple_check_get_groups_send(TALLOC_CTX *mem_ctx,
                             struct tevent_context *ev,
                             struct simple_ctx *ctx,
                             const char *username)
{
    errno_t ret;
    struct tevent_req *req;
    struct tevent_req *subreq;
    struct simple_check_groups_state *state;
    const char *attrs[] = { SYSDB_NAME, SYSDB_POSIX, SYSDB_GIDNUM, NULL };
    size_t group_count;
    struct ldb_message *user;
    struct ldb_message **groups;
    int i;
    gid_t gid;
    char *cname;

    req = tevent_req_create(mem_ctx, &state,
                            struct simple_check_groups_state);
    if (!req) return NULL;

    state->ev = ev;
    state->ctx = ctx;

    cname = sss_get_cased_name(state, username, ctx->domain->case_sensitive);
    if (!cname) {
        ret = ENOMEM;
        goto done;
    }

    DEBUG(SSSDBG_TRACE_LIBS, ("Looking up groups for user %s\n", cname));

    ret = sysdb_search_user_by_name(state, ctx->domain->sysdb,
                                    cname, attrs, &user);
    if (ret == ENOENT) {
        DEBUG(SSSDBG_MINOR_FAILURE, ("No such user %s\n", cname));
        goto done;
    } else if (ret != EOK) {
        DEBUG(SSSDBG_OP_FAILURE,
              ("Could not look up username [%s]: [%d][%s]\n",
              username, ret, strerror(ret)));
        goto done;
    }

    ret = sysdb_asq_search(state, ctx->domain->sysdb,
                           user->dn, NULL, SYSDB_MEMBEROF,
                           attrs, &group_count, &groups);
    if (ret != EOK) {
        goto done;
    }

    DEBUG(SSSDBG_TRACE_FUNC,
          ("User %s is a member of %d supplemental groups\n",
           cname, group_count));

    /* One extra space for terminator, one extra space for private group */
    state->group_names = talloc_zero_array(state, const char *, group_count + 2);
    state->lookup_gids = talloc_zero_array(state, gid_t, group_count + 2);
    if (!state->group_names || !state->lookup_gids) {
        ret = ENOMEM;
        goto done;
    }

    for (i=0; i < group_count; i++) {
        /* Some providers (like the AD provider) might perform initgroups
         * without resolving the group names. In order for the simple access
         * provider to work correctly, we need to resolve the groups before
         * performing the access check. In AD provider, the situation is
         * even more tricky b/c the groups HAVE name, but their name
         * attribute is set to SID and they are set as non-POSIX
         */
        ret = simple_check_process_group(state, groups[i]);
        if (ret != EOK) {
            goto done;
        }
    }

    gid = ldb_msg_find_attr_as_uint64(user, SYSDB_GIDNUM, 0);
    if (!gid) {
        DEBUG(SSSDBG_MINOR_FAILURE, ("User %s has no gid?\n", cname));
        ret = EINVAL;
        goto done;
    }

    ret = simple_check_get_groups_primary(state, gid);
    if (ret != EOK) {
        goto done;
    }

    if (state->num_gids == 0) {
        /* If all groups could have been resolved by name, we are
         * done
         */
        DEBUG(SSSDBG_TRACE_FUNC, ("All groups had name attribute\n"));
        ret = EOK;
        goto done;
    }

    DEBUG(SSSDBG_TRACE_FUNC, ("Need to resolve %d groups\n", state->num_gids));
    state->giter = 0;
    subreq = simple_resolve_group_send(req, state->ev, state->ctx,
                                       state->lookup_gids[state->giter]);
    if (!subreq) {
        ret = ENOMEM;
        goto done;
    }
    tevent_req_set_callback(subreq, simple_check_get_groups_next, req);

    return req;

done:
    if (ret == EOK) {
        tevent_req_done(req);
    } else {
        tevent_req_error(req, ret);
    }
    tevent_req_post(req, ev);
    return req;
}

static void simple_check_get_groups_next(struct tevent_req *subreq)
{
    struct tevent_req *req =
                        tevent_req_callback_data(subreq, struct tevent_req);
    struct simple_check_groups_state *state =
                        tevent_req_data(req, struct simple_check_groups_state);
    errno_t ret;

    ret = simple_resolve_group_recv(subreq, state->group_names,
                                    &state->group_names[state->num_names]);
    talloc_zfree(subreq);
    if (ret != EOK) {
        DEBUG(SSSDBG_OP_FAILURE,
              ("Could not resolve name of group with GID %llu\n",
              state->lookup_gids[state->giter]));
        tevent_req_error(req, ret);
        return;
    }

    state->num_names++;
    state->giter++;

    if (state->giter < state->num_gids) {
        subreq = simple_resolve_group_send(req, state->ev, state->ctx,
                                           state->lookup_gids[state->giter]);
        if (!subreq) {
            tevent_req_error(req, ENOMEM);
            return;
        }
        tevent_req_set_callback(subreq, simple_check_get_groups_next, req);
        return;
    }

    DEBUG(SSSDBG_TRACE_INTERNAL, ("All groups resolved. Done.\n"));
    tevent_req_done(req);
}

static errno_t
simple_check_process_group(struct simple_check_groups_state *state,
                           struct ldb_message *group)
{
    const char *name;
    gid_t gid;
    bool posix;

    posix = is_posix(group);
    name = ldb_msg_find_attr_as_string(group, SYSDB_NAME, NULL);
    gid = ldb_msg_find_attr_as_uint64(group, SYSDB_GIDNUM, 0);

    /* With the current sysdb layout, every group has a name */
    if (name == NULL) {
        return EINVAL;
    }

    if (gid == 0) {
        if (posix == true) {
            DEBUG(SSSDBG_CRIT_FAILURE, ("POSIX group without GID\n"));
            return EINVAL;
        }

        /* Non-posix group with a name. Still can be used for access
         * control as the name should point to the real name, no SID
         */
        state->group_names[state->num_names] = talloc_strdup(state->group_names,
                                                             name);
        if (!state->group_names[state->num_names]) {
            return ENOMEM;
        }
        DEBUG(SSSDBG_TRACE_INTERNAL, ("Adding group %s\n", name));
        state->num_names++;
        return EOK;
    }

    /* Here are only groups with a name and gid. POSIX group can already
     * be used, non-POSIX groups can be resolved */
    if (posix) {
        state->group_names[state->num_names] = talloc_strdup(state->group_names,
                                                             name);
        if (!state->group_names[state->num_names]) {
            return ENOMEM;
        }
        DEBUG(SSSDBG_TRACE_INTERNAL, ("Adding group %s\n", name));
        state->num_names++;
        return EOK;
    }

    /* Non-posix group with a GID. Needs resolving */
    state->lookup_gids[state->num_gids] = gid;
    DEBUG(SSSDBG_TRACE_INTERNAL, ("Adding GID %llu\n", gid));
    state->num_gids++;
    return EOK;
}

static errno_t
simple_check_get_groups_primary(struct simple_check_groups_state *state,
                                gid_t gid)
{
    errno_t ret;
    const char *group_attrs[] = { SYSDB_NAME, SYSDB_POSIX,
                                  SYSDB_GIDNUM, NULL };
    struct ldb_message *msg;

    ret = sysdb_search_group_by_gid(state, state->ctx->domain->sysdb,
                                    gid, group_attrs, &msg);
    if (ret != EOK) {
        DEBUG(SSSDBG_OP_FAILURE,
               ("Could not look up primary group [%lu]: [%d][%s]\n",
               gid, ret, strerror(ret)));
        /* We have to treat this as non-fatal, because the primary
         * group may be local to the machine and not available in
         * our ID provider.
         */
    } else {
        ret = simple_check_process_group(state, msg);
        if (ret != EOK) {
            DEBUG(SSSDBG_OP_FAILURE, ("Cannot process primary group\n"));
            return ret;
        }
    }

    return EOK;
}

static errno_t
simple_check_get_groups_recv(struct tevent_req *req,
                             TALLOC_CTX *mem_ctx,
                             const char ***_group_names)
{
    struct simple_check_groups_state *state;

    state = tevent_req_data(req, struct simple_check_groups_state);

    TEVENT_REQ_RETURN_ON_ERROR(req);

    *_group_names = talloc_steal(mem_ctx, state->group_names);
    return EOK;
}

struct simple_access_check_state {
    bool access_granted;
    struct simple_ctx *ctx;
    const char *username;

    const char **group_names;
};

static void simple_access_check_done(struct tevent_req *subreq);

struct tevent_req *simple_access_check_send(TALLOC_CTX *mem_ctx,
                                            struct tevent_context *ev,
                                            struct simple_ctx *ctx,
                                            const char *username)
{
    errno_t ret;
    struct tevent_req *req;
    struct tevent_req *subreq;
    struct simple_access_check_state *state;

    req = tevent_req_create(mem_ctx, &state,
                            struct simple_access_check_state);
    if (!req) return NULL;

    state->access_granted = false;
    state->ctx = ctx;
    state->username = talloc_strdup(state, username);
    if (!state->username) {
        ret = ENOMEM;
        goto immediate;
    }

    DEBUG(SSSDBG_FUNC_DATA, ("Simple access check for %s\n", username));

    ret = simple_check_users(ctx, username, &state->access_granted);
    if (ret != EAGAIN) {
        /* Both access denied and an error */
        goto immediate;
    }

    if (!ctx->allow_groups && !ctx->deny_groups) {
        /* There are no group restrictions, so just return
         * here with whatever we've decided.
         */
        DEBUG(SSSDBG_TRACE_LIBS, ("No group restrictions, end request\n"));
        ret = EOK;
        goto immediate;
    }

    /* The group names might not be available. Fire a request to
     * gather them. In most cases, the request will just shortcut
     */
    subreq = simple_check_get_groups_send(state, ev, ctx, username);
    if (!subreq) {
        ret = EIO;
        goto immediate;
    }
    tevent_req_set_callback(subreq, simple_access_check_done, req);

    return req;

immediate:
    if (ret == EOK) {
        tevent_req_done(req);
    } else {
        tevent_req_error(req, ret);
    }
    tevent_req_post(req, ev);
    return req;
}


static void simple_access_check_done(struct tevent_req *subreq)
{
    struct tevent_req *req =
                        tevent_req_callback_data(subreq, struct tevent_req);
    struct simple_access_check_state *state =
                        tevent_req_data(req, struct simple_access_check_state);
    errno_t ret;

    /* We know the names now. Run the check. */
    ret = simple_check_get_groups_recv(subreq, state, &state->group_names);
    talloc_zfree(subreq);
    if (ret == ENOENT) {
        /* If the user wasn't found, just shortcut */
        state->access_granted = false;
        tevent_req_done(req);
        return;
    } else if (ret != EOK) {
        DEBUG(SSSDBG_OP_FAILURE,
              ("Could not collect groups of user %s\n", state->username));
        tevent_req_error(req, ret);
        return;
    }

    ret = simple_check_groups(state->ctx, state->username,
                              state->group_names, &state->access_granted);
    if (ret != EOK) {
        tevent_req_error(req, ret);
        return;
    }

    /* Now just return whatever we decided */
    DEBUG(SSSDBG_TRACE_INTERNAL, ("Group check done\n"));
    tevent_req_done(req);
}

errno_t simple_access_check_recv(struct tevent_req *req, bool *access_granted)
{
    struct simple_access_check_state *state =
                        tevent_req_data(req, struct simple_access_check_state);

    TEVENT_REQ_RETURN_ON_ERROR(req);

    DEBUG(SSSDBG_TRACE_LIBS,
          ("Access %sgranted\n", state->access_granted ? "" : "not "));
    if (access_granted) {
        *access_granted = state->access_granted;
    }

    return EOK;
}