IPA: handle searches by SID in apply_subdomain_homedir

https://fedorahosted.org/sssd/ticket/2391

apply_subdomain_homedir() didn't handle the situation where an entity
that doesn't match was requested from the cache. For user and group
lookups this wasn't a problem because the negative match was caught
sooner.

But SID lookups can match either user or group. When a group SID was
requested, the preceding LDAP request matched the SID and stored the
group in the cache. Then apply_subdomain_homedir() only tried to search
user by SID, didn't find the entry and accessed a NULL pointer.

A simple reproducer is:
$ python
>>> import pysss_nss_idmap
>>> pysss_nss_idmap.getnamebysid(group_sid)

The group_sid can be anything, including Domain Users (XXX-513)

Reviewed-by: Michal Židek <mzidek@redhat.com>
(cherry picked from commit 82347f452febe3cbffc36b0a3308ffb462515442)

1 files changed, 9 insertions, 4 deletions

diff --git a/src/providers/ipa/ipa_subdomains_id.c b/src/providers/ipa/ipa_subdomains_id.c
index d8922a461..5517602a6 100644
--- a/src/providers/ipa/ipa_subdomains_id.c
+++ b/src/providers/ipa/ipa_subdomains_id.c
@@ -492,6 +492,9 @@ apply_subdomain_homedir(TALLOC_CTX *mem_ctx, struct sss_domain_info *dom,
 
     if (filter_type == BE_FILTER_NAME) {
         ret = sysdb_getpwnam(mem_ctx, dom->sysdb, dom, filter_value, &res);
+        if (res && res->count == 0) {
+            ret = ENOENT;
+        }
     } else if (filter_type == BE_FILTER_IDNUM) {
         errno = 0;
         uid = strtouint32(filter_value, NULL, 10);
@@ -500,6 +503,9 @@ apply_subdomain_homedir(TALLOC_CTX *mem_ctx, struct sss_domain_info *dom,
             goto done;
         }
         ret = sysdb_getpwuid(mem_ctx, dom->sysdb, dom, uid, &res);
+        if (res && res->count == 0) {
+            ret = ENOENT;
+        }
     } else if (filter_type == BE_FILTER_SECID) {
         ret = sysdb_search_user_by_sid_str(mem_ctx, dom->sysdb, dom,
                                            filter_value, attrs, &msg);
@@ -515,10 +521,9 @@ apply_subdomain_homedir(TALLOC_CTX *mem_ctx, struct sss_domain_info *dom,
               ("Failed to make request to our cache: [%d]: [%s]\n",
                ret, sss_strerror(ret)));
         goto done;
-    }
-
-    if ((res && res->count == 0) || (msg && msg->num_elements == 0)) {
-        ret = ENOENT;
+    } else if (ret == ENOENT) {
+        DEBUG(SSSDBG_TRACE_FUNC, ("Cannot find [%s] with search type [%d]\n",
+              filter_value, filter_type));
         goto done;
     }