CVE-2024-33600: nscd: Avoid null pointer crashes after notfound response (bug 31678)

The addgetnetgrentX call in addinnetgrX may have failed to produce
a result, so the result variable in addinnetgrX can be NULL.
Use db->negtimeout as the fallback value if there is no result data;
the timeout is also overwritten below.

Also avoid sending a second not-found response.  (The client
disconnects after receiving the first response, so the data stream did
not go out of sync even without this fix.)  It is still beneficial to
add the negative response to the mapping, so that the client can get
it from there in the future, instead of going through the socket.

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

diff --git a/nscd/netgroupcache.c b/nscd/netgroupcache.c
index c18fe111f37496d7ef949a706a555d697bdf6e68..e22ffa5884e36260b7a45a029a963946d337a533 100644 (file)
--- a/nscd/netgroupcache.c
+++ b/nscd/netgroupcache.c
@@ -511,14 +511,15 @@ addinnetgrX (struct database_dyn *db, int fd, request_header *req,
 
   datahead_init_pos (&dataset->head, sizeof (*dataset) + req->key_len,
                     sizeof (innetgroup_response_header),
-                    he == NULL ? 0 : dh->nreloads + 1, result->head.ttl);
+                    he == NULL ? 0 : dh->nreloads + 1,
+                    result == NULL ? db->negtimeout : result->head.ttl);
   /* Set the notfound status and timeout based on the result from
      getnetgrent.  */
-  dataset->head.notfound = result->head.notfound;
+  dataset->head.notfound = result == NULL || result->head.notfound;
   dataset->head.timeout = timeout;
 
   dataset->resp.version = NSCD_VERSION;
-  dataset->resp.found = result->resp.found;
+  dataset->resp.found = result != NULL && result->resp.found;
   /* Until we find a matching entry the result is 0.  */
   dataset->resp.result = 0;
 
@@ -566,7 +567,9 @@ addinnetgrX (struct database_dyn *db, int fd, request_header *req,
       goto out;
     }
 
-  if (he == NULL)
+  /* addgetnetgrentX may have already sent a notfound response.  Do
+     not send another one.  */
+  if (he == NULL && dataset->resp.found)
     {
       /* We write the dataset before inserting it to the database
         since while inserting this thread might block and so would