[PATCH 4.19 19/30] netfilter: conntrack: re-fetch conntrack after insertion

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Florian Westphal <fw@strlen.de>

commit 56b14ecec97f39118bf85c9ac2438c5a949509ed upstream.

In case the conntrack is clashing, insertion can free skb->_nfct and
set skb->_nfct to the already-confirmed entry.

This wasn't found before because the conntrack entry and the extension
space used to free'd after an rcu grace period, plus the race needs
events enabled to trigger.

Reported-by: <syzbot+793a590957d9c1b96620@syzkaller.appspotmail.com>
Fixes: 71d8c47fc653 ("netfilter: conntrack: introduce clash resolution on insertion race")
Fixes: 2ad9d7747c10 ("netfilter: conntrack: free extension area immediately")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 include/net/netfilter/nf_conntrack_core.h |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/include/net/netfilter/nf_conntrack_core.h
+++ b/include/net/netfilter/nf_conntrack_core.h
@@ -58,8 +58,13 @@ static inline int nf_conntrack_confirm(s
 	int ret = NF_ACCEPT;
 
 	if (ct) {
-		if (!nf_ct_is_confirmed(ct))
+		if (!nf_ct_is_confirmed(ct)) {
 			ret = __nf_conntrack_confirm(skb);
+
+			if (ret == NF_ACCEPT)
+				ct = (struct nf_conn *)skb_nfct(skb);
+		}
+
 		if (likely(ret == NF_ACCEPT))
 			nf_ct_deliver_cached_events(ct);
 	}