[glibc/release/2.37/master] CVE-2024-33600: nscd: Avoid null pointer crashes after notfound response (bug 31678)

[glibc/release/2.37/master] CVE-2024-33600: nscd: Avoid null pointer crashes after notfound response (bug 31678)

[Florian Weimer]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=a8070b31043c7585c36ba68a74298c4f7af075c3

commit a8070b31043c7585c36ba68a74298c4f7af075c3
Author: Florian Weimer <fweimer@redhat.com>
Date:   Thu Apr 25 15:01:07 2024 +0200

    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>
    (cherry picked from commit b048a482f088e53144d26a61c390bed0210f49f2)

Diff:
---
 nscd/netgroupcache.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/nscd/netgroupcache.c b/nscd/netgroupcache.c
index 52dc68aa20..fe5d10226b 100644
--- 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