BUG/MEDIUM: resolvers: Test for empty tree when getting a record from DNS answer

In the previous fix 5d1d93fad ("BUG/MEDIUM: resolvers: Properly handle empty
tree when getting a record from the DNS answer"), I missed the fact the
answer tree can be empty.

So, to avoid crashes, when the answer tree is empty, we immediately exit
from resolv_get_ip_from_response() function with RSLV_UPD_NO_IP_FOUND. In
addition, when a record is removed from the tree, we take care to reset the
next node saved if necessary.

This patch must be backported with the commit above.

diff --git a/src/resolvers.c b/src/resolvers.c
index a42ae9133738184b2570a0193042e0d7d727d793..285411c419567bb385804998fb0ce65749cdcfb6 100644 (file)
--- a/src/resolvers.c
+++ b/src/resolvers.c
@@ -818,6 +818,8 @@ static void resolv_check_response(struct resolv_resolution *res)
                                        resolv_srvrq_cleanup_srv(srv);
                        }
 
+                       if (eb32 == res->response.next)
+                               res->response.next = NULL;
                        eb32_delete(&item->link);
                        if (item->ar_item) {
                                pool_free(resolv_answer_item_pool, item->ar_item);
@@ -1627,6 +1629,10 @@ int resolv_get_ip_from_response(struct resolv_response *r_res,
        if (owner && LIST_INLIST(&owner->ip_rec_item))
                return RSLV_UPD_NO;
 
+       /* there is no record in the answer tree */
+       if (eb_is_empty(&r_res->answer_tree))
+               return RSLV_UPD_NO_IP_FOUND;
+
        family_priority   = resolv_opts->family_prio;
        allowed_duplicated_ip = resolv_opts->accept_duplicate_ip;
        *newip = newip4   = newip6 = NULL;
@@ -1992,6 +1998,7 @@ static void resolv_purge_resolution_answer_records(struct resolv_resolution *res
        struct eb32_node *eb32, *eb32_back;
        struct resolv_answer_item *item;
 
+       resolution->response.next = NULL;
        for (eb32 = eb32_first(&resolution->response.answer_tree);
             eb32 && (eb32_back = eb32_next(eb32), 1);
             eb32 = eb32_back) {