netfilter: conntrack: re-fetch conntrack after insertion

BugLink: https://bugs.launchpad.net/bugs/1981862
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>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/include/net/netfilter/nf_conntrack_core.h b/include/net/netfilter/nf_conntrack_core.h
index 13807ea94cd2b46bbd08e020623745b224590bb3..2d524782f53b797c03ccf87f321f7910c9632f9e 100644 (file)
--- 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 (likely(ret == NF_ACCEPT))
                        nf_ct_deliver_cached_events(ct);
        }