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netfilter: conntrack: re-fetch conntrack after insertion

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commit 56b14ecec9 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: 71d8c47fc6 ("netfilter: conntrack: introduce clash resolution on insertion race")
Fixes: 2ad9d7747c ("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>
This commit is contained in:
Florian Westphal 2022-05-20 00:02:04 +02:00 • committed by Greg Kroah-Hartman
commit 91a36ec160
1 changed files with 6 additions and 1 deletions
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7
include/net/netfilter/nf_conntrack_core.h
View file

@ -59,8 +59,13 @@ 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 (likely(ret == NF_ACCEPT))
nf_ct_deliver_cached_events(ct);
}