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netfilter: nf_conntrack: fix a race in __nf_conntrack_confirm against nf_ct_get_next_corpse()

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This race was triggered by a 'conntrack -F' command running in parallel
to the insertion of a hash for a new connection. Losing this race led to
a dead conntrack entry effectively blocking traffic for a particular
connection until timeout or flushing the conntrack hashes again.
Now the check for an already dying connection is done inside the lock.

Signed-off-by: Joerg Marx <[email protected]>
Signed-off-by: Patrick McHardy <[email protected]>
This commit is contained in:
Joerg Marx 2010-05-20 15:55:30 +02:00 • committed by Patrick McHardy
commit fc350777c7
2 changed files with 11 additions and 1 deletions
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10
net/netfilter/nf_conntrack_core.c
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@ -424,6 +424,16 @@ __nf_conntrack_confirm(struct sk_buff *skb)
spin_lock_bh(&nf_conntrack_lock);
/* We have to check the DYING flag inside the lock to prevent
a race against nf_ct_get_next_corpse() possibly called from
user context, else we insert an already 'dead' hash, blocking
further use of that particular connection -JM */
if (unlikely(nf_ct_is_dying(ct))) {
spin_unlock_bh(&nf_conntrack_lock);
return NF_ACCEPT;
}
/* See if there's one in the list already, including reverse:
NAT could have grabbed it without realizing, since we're
not in the hash. If there is, we lost race. */