netdev - [PATCH net 2/4] netfilter: conntrack: re-fetch conntrack after insertion

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Date:   Fri, 27 May 2022 11:20:21 +0200
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     netfilter-devel@...r.kernel.org
Cc:     davem@...emloft.net, netdev@...r.kernel.org, kuba@...nel.org,
        pabeni@...hat.com
Subject: [PATCH net 2/4] netfilter: conntrack: re-fetch conntrack after insertion

From: Florian Westphal <fw@...len.de>

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@...kaller.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@...len.de>
Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
---
 include/net/netfilter/nf_conntrack_core.h | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/include/net/netfilter/nf_conntrack_core.h b/include/net/netfilter/nf_conntrack_core.h
index 6406cfee34c2..37866c8386e2 100644
--- 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(struct sk_buff *skb)
 	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 (ret == NF_ACCEPT && nf_ct_ecache_exist(ct))
 			nf_ct_deliver_cached_events(ct);
 	}
-- 
2.30.2