netfilter: ipv6: nf_defrag: fix NULL deref panic

Valdis reports NULL deref in nf_ct_frag6_gather.
Problem is bogus use of skb_queue_walk() -- we miss first skb in the list
since we start with head->next instead of head.

In case the element we're looking for was head->next we won't find
a result and then trip over NULL iter.

(defrag uses plain NULL-terminated list rather than one terminated by
 head-of-list-pointer, which is what skb_queue_walk expects).

Fixes: 029f7f3b8701cc7a ("netfilter: ipv6: nf_defrag: avoid/free clone operations")
Reported-by: Valdis Kletnieks <Valdis.Kletnieks@vt.edu>
Tested-by: Valdis Kletnieks <Valdis.Kletnieks@vt.edu>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/net/ipv6/netfilter/nf_conntrack_reasm.c b/net/ipv6/netfilter/nf_conntrack_reasm.c
index 912bc3afc183a1400fc6e0fff214e967443e3af5..6e5f0e0d49e0f29291d24d0ce5782d3bfb3f6202 100644 (file)
--- a/net/ipv6/netfilter/nf_conntrack_reasm.c
+++ b/net/ipv6/netfilter/nf_conntrack_reasm.c
@@ -441,11 +441,14 @@ nf_ct_frag6_reasm(struct frag_queue *fq, struct sk_buff *prev,  struct net_devic
                        return false;
 
                fp->next = prev->next;
-               skb_queue_walk(head, iter) {
-                       if (iter->next != prev)
-                               continue;
-                       iter->next = fp;
-                       break;
+
+               iter = head;
+               while (iter) {
+                       if (iter->next == prev) {
+                               iter->next = fp;
+                               break;
+                       }
+                       iter = iter->next;
                }
 
                skb_morph(prev, head);