[PATCH AUTOSEL 4.19 02/73] netfilter: ipv6: fix oops when defragmenting locally generated fragments

[Sasha Levin]

From: Florian Westphal <fw@xxxxxxxxx>

[ Upstream commit 61792b677415b77c8db04991c22966bb8de7603e ]

Unlike ipv4 and normal ipv6 defrag, netfilter ipv6 defragmentation did
not save/restore skb->dst.

This causes oops when handling locally generated ipv6 fragments, as
output path needs a valid dst.

Reported-by: Maciej Åenczykowski <zenczykowski@xxxxxxxxx>
Fixes: 84379c9afe01 ("netfilter: ipv6: nf_defrag: drop skb dst before queueing")
Signed-off-by: Florian Westphal <fw@xxxxxxxxx>
Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 net/ipv6/netfilter/nf_conntrack_reasm.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/net/ipv6/netfilter/nf_conntrack_reasm.c b/net/ipv6/netfilter/nf_conntrack_reasm.c
index 8f68a518d9db..f76bd4d15704 100644
--- a/net/ipv6/netfilter/nf_conntrack_reasm.c
+++ b/net/ipv6/netfilter/nf_conntrack_reasm.c
@@ -587,11 +587,16 @@ int nf_ct_frag6_gather(struct net *net, struct sk_buff *skb, u32 user)
 	 */
 	ret = -EINPROGRESS;
 	if (fq->q.flags == (INET_FRAG_FIRST_IN | INET_FRAG_LAST_IN) &&
-	    fq->q.meat == fq->q.len &&
-	    nf_ct_frag6_reasm(fq, skb, dev))
-		ret = 0;
-	else
+	    fq->q.meat == fq->q.len) {
+		unsigned long orefdst = skb->_skb_refdst;
+
+		skb->_skb_refdst = 0UL;
+		if (nf_ct_frag6_reasm(fq, skb, dev))
+			ret = 0;
+		skb->_skb_refdst = orefdst;
+	} else {
 		skb_dst_drop(skb);
+	}
 
 out_unlock:
 	spin_unlock_bh(&fq->q.lock);
-- 
2.17.1