netdev - [PATCH 4.4 stable 05/10] netfilter: ipv6: nf

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Date:   Tue,  8 Oct 2019 13:23:04 +0200
From:   Georg Kohmann <geokohma@...co.com>
To:     netdev@...r.kernel.org
Cc:     Georg Kohmann <geokohma@...co.com>,
        Florian Westphal <fw@...len.de>,
        Pablo Neira Ayuso <pablo@...filter.org>
Subject: [PATCH 4.4 stable 05/10] netfilter: ipv6: nf_defrag: fix NULL deref panic

commit e97ac12859db ("netfilter: ipv6: nf_defrag: fix NULL deref panic")
Author: Florian Westphal <fw@...len.de>
Date:   Tue Dec 8 23:35:19 2015 +0100

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@...edu>
Tested-by: Valdis Kletnieks <Valdis.Kletnieks@...edu>
Signed-off-by: Florian Westphal <fw@...len.de>
Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
---
 net/ipv6/netfilter/nf_conntrack_reasm.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/net/ipv6/netfilter/nf_conntrack_reasm.c b/net/ipv6/netfilter/nf_conntrack_reasm.c
index 394aeb1..5640e041 100644
--- a/net/ipv6/netfilter/nf_conntrack_reasm.c
+++ b/net/ipv6/netfilter/nf_conntrack_reasm.c
@@ -415,11 +415,14 @@ 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);
-- 
2.10.2