Add PAC to master host TGTs

For a proper SASL bind with GSSAPI against an AD LDAP server a PAC is
needed. To allow SSSD in ipa_server_mode to access the LDAP or GC server
of a trusted domain with the credentials of a FreeIPA server host a
PAC must be added to the TGT for the host.

We use the well know RID of the Domain Computers group (515) for the
primary gid element of the PAC, this is the same as AD uses for host
tickets.  The rid element of the PAC is set to the well know RID of the
Domain Controllers group (516). This is working for the SSSD use case
but might be improved later for more general use cases.

To determine if a host is a FreeIPA server or not it is checked if there
is an entry for the host in cn=master,cn=ipa,cn=etc,$base. Unfortunately
this requires an additional LDAP lookup. But since TGS-REQs for hosts
should be rare I think it is acceptable for the time being.

Fixes https://fedorahosted.org/freeipa/ticket/3651

1 files changed, 115 insertions, 39 deletions

diff --git a/daemons/ipa-kdb/ipa_kdb_mspac.c b/daemons/ipa-kdb/ipa_kdb_mspac.c
index 2662b947b..92dc8dd7f 100644
--- a/daemons/ipa-kdb/ipa_kdb_mspac.c
+++ b/daemons/ipa-kdb/ipa_kdb_mspac.c
@@ -58,6 +58,7 @@ static char *user_pac_attrs[] = {
     "objectClass",
     "uid",
     "cn",
+    "fqdn",
     "gidNumber",
     "krbPrincipalName",
     "krbCanonicalName",
@@ -358,6 +359,29 @@ static int sid_split_rid(struct dom_sid *sid, uint32_t *rid)
     return 0;
 }
 
+static bool is_master_host(struct ipadb_context *ipactx, const char *fqdn)
+{
+    int ret;
+    char *master_host_base = NULL;
+    LDAPMessage *result = NULL;
+    krb5_error_code err;
+
+    ret = asprintf(&master_host_base, "cn=%s,cn=masters,cn=ipa,cn=etc,%s",
+                                      fqdn, ipactx->base);
+    if (ret == -1) {
+        return false;
+    }
+    err = ipadb_simple_search(ipactx, master_host_base, LDAP_SCOPE_BASE,
+                              NULL, NULL, &result);
+    free(master_host_base);
+    ldap_msgfree(result);
+    if (err == 0) {
+        return true;
+    }
+
+    return false;
+}
+
 static krb5_error_code ipadb_fill_info3(struct ipadb_context *ipactx,
                                         LDAPMessage *lentry,
                                         TALLOC_CTX *memctx,
@@ -371,13 +395,65 @@ static krb5_error_code ipadb_fill_info3(struct ipadb_context *ipactx,
     char *strres;
     int intres;
     int ret;
+    char **objectclasses = NULL;
+    size_t c;
+    bool is_host = false;
+    bool is_user = false;
+
+    ret = ipadb_ldap_attr_to_strlist(lcontext, lentry, "objectClass",
+                                     &objectclasses);
+    if (ret == 0 && objectclasses != NULL) {
+        for (c = 0; objectclasses[c] != NULL; c++) {
+            if (strcasecmp(objectclasses[c], "ipaHost") == 0) {
+                is_host = true;
+            }
+            if (strcasecmp(objectclasses[c], "ipaNTUserAttrs") == 0) {
+                is_user = true;
+            }
+            free(objectclasses[c]);
+        }
+    }
+    free(objectclasses);
 
-    ret = ipadb_ldap_attr_to_int(lcontext, lentry, "gidNumber", &intres);
-    if (ret) {
-        /* gidNumber is mandatory */
-        return ret;
+    if (!is_host && !is_user) {
+        /* We only handle users and hosts */
+        return ENOENT;
+    }
+
+    if (is_host) {
+        ret = ipadb_ldap_attr_to_str(lcontext, lentry, "fqdn", &strres);
+        if (ret) {
+            /* fqdn is mandatory for hosts */
+            return ret;
+        }
+
+        /* Currently we only add a PAC to TGTs for IPA servers to allow SSSD in
+         * ipa_server_mode to access the AD LDAP server */
+        if (!is_master_host(ipactx, strres)) {
+            free(strres);
+            return ENOENT;
+        }
+    } else {
+        ret = ipadb_ldap_attr_to_str(lcontext, lentry, "uid", &strres);
+        if (ret) {
+            /* uid is mandatory */
+            return ret;
+        }
+    }
+
+    info3->base.account_name.string = talloc_strdup(memctx, strres);
+    free(strres);
+
+    if (is_host) {
+        prigid = 515; /* Well known RID for domain computers group */
+    } else {
+        ret = ipadb_ldap_attr_to_int(lcontext, lentry, "gidNumber", &intres);
+        if (ret) {
+            /* gidNumber is mandatory */
+            return ret;
+        }
+        prigid = intres;
     }
-    prigid = intres;
 
 
     info3->base.logon_time = 0; /* do not have this info yet */
@@ -419,15 +495,6 @@ static krb5_error_code ipadb_fill_info3(struct ipadb_context *ipactx,
     info3->base.allow_password_change = 0;
     info3->base.force_password_change = -1;
 
-    /* FIXME: handle computer accounts they do not use 'uid' */
-    ret = ipadb_ldap_attr_to_str(lcontext, lentry, "uid", &strres);
-    if (ret) {
-        /* uid is mandatory */
-        return ret;
-    }
-    info3->base.account_name.string = talloc_strdup(memctx, strres);
-    free(strres);
-
     ret = ipadb_ldap_attr_to_str(lcontext, lentry, "cn", &strres);
     switch (ret) {
     case 0:
@@ -500,21 +567,25 @@ static krb5_error_code ipadb_fill_info3(struct ipadb_context *ipactx,
     info3->base.logon_count = 0; /* we do not have this info yet */
     info3->base.bad_password_count = 0; /* we do not have this info yet */
 
-    ret = ipadb_ldap_attr_to_str(lcontext, lentry,
-                                 "ipaNTSecurityIdentifier", &strres);
-    if (ret) {
-        /* SID is mandatory */
-        return ret;
-    }
-    ret = string_to_sid(strres, &sid);
-    free(strres);
-    if (ret) {
-        return ret;
-    }
-
-    ret = sid_split_rid(&sid, &info3->base.rid);
-    if (ret) {
-        return ret;
+    if (is_host) {
+        /* Well know RID of domain controllers group */
+        info3->base.rid = 516;
+    } else {
+        ret = ipadb_ldap_attr_to_str(lcontext, lentry,
+                                     "ipaNTSecurityIdentifier", &strres);
+        if (ret) {
+            /* SID is mandatory */
+            return ret;
+        }
+        ret = string_to_sid(strres, &sid);
+        free(strres);
+        if (ret) {
+            return ret;
+        }
+        ret = sid_split_rid(&sid, &info3->base.rid);
+        if (ret) {
+            return ret;
+        }
     }
 
     ret = ipadb_ldap_deref_results(lcontext, lentry, &deref_results);
@@ -587,11 +658,15 @@ static krb5_error_code ipadb_fill_info3(struct ipadb_context *ipactx,
     }
 
     if (info3->base.primary_gid == 0) {
-        if (ipactx->mspac->fallback_rid) {
-            info3->base.primary_gid = ipactx->mspac->fallback_rid;
+        if (is_host) {
+            info3->base.primary_gid = 515;  /* Well known RID for domain computers group */
         } else {
-            /* can't give a pack without a primary group rid */
-            return ENOENT;
+            if (ipactx->mspac->fallback_rid) {
+                info3->base.primary_gid = ipactx->mspac->fallback_rid;
+            } else {
+                /* can't give a pack without a primary group rid */
+                return ENOENT;
+            }
         }
     }
 
@@ -623,8 +698,13 @@ static krb5_error_code ipadb_fill_info3(struct ipadb_context *ipactx,
         return ENOENT;
     }
 
-    /* we got the domain SID for the user sid */
-    info3->base.domain_sid = talloc_memdup(memctx, &sid, sizeof(sid));
+    if (is_host) {
+        info3->base.domain_sid = talloc_memdup(memctx, &ipactx->mspac->domsid,
+                                               sizeof(ipactx->mspac->domsid));
+    } else {
+        /* we got the domain SID for the user sid */
+        info3->base.domain_sid = talloc_memdup(memctx, &sid, sizeof(sid));
+    }
 
     /* always zero out, not used for Krb, only NTLM */
     memset(&info3->base.LMSessKey, '\0', sizeof(info3->base.key));
@@ -666,10 +746,6 @@ static krb5_error_code ipadb_get_pac(krb5_context kcontext,
         return EINVAL;
     }
 
-    if (!ied->ipa_user) {
-        return 0;
-    }
-
     tmpctx = talloc_new(NULL);
     if (!tmpctx) {
         return ENOMEM;