IPA: Handle bad results from c-ares lookup

In some situations, the c-ares lookup can return NULL instead of
a list of addresses. In this situation, we need to avoid
dereferencing NULL.

This patch adds a log message and sets the count to zero so it is
handled appropriately below.

1 files changed, 11 insertions, 1 deletions

diff --git a/src/providers/ipa/ipa_dyndns.c b/src/providers/ipa/ipa_dyndns.c
index 3f430a33..9d7a5b6c 100644
--- a/src/providers/ipa/ipa_dyndns.c
+++ b/src/providers/ipa/ipa_dyndns.c
@@ -733,7 +733,17 @@ ipa_dyndns_update_get_addrs_done(struct tevent_req *subreq)
 
     /* EOK */
 
-    for (count=0; rhostent->addr_list[count]; count++);
+    if (rhostent->addr_list) {
+        for (count=0; rhostent->addr_list[count]; count++);
+    } else {
+        /* The address list is NULL. This is probably a bug in
+         * c-ares, but we need to handle it gracefully.
+         */
+        DEBUG(SSSDBG_MINOR_FAILURE,
+              ("Lookup of [%s] returned no addresses. Skipping.\n",
+               rhostent->name));
+        count = 0;
+    }
 
     state->addrlist = talloc_realloc(state, state->addrlist, char *,
                                         state->count + count + 1);