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netfilter: conntrack: fix race in __nf_conntrack_confirm against get_next_corpse

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After removal of the central spinlock nf_conntrack_lock, in
commit 93bb0ceb75 ("netfilter: conntrack: remove central
spinlock nf_conntrack_lock"), it is possible to race against
get_next_corpse().

The race is against the get_next_corpse() cleanup on
the "unconfirmed" list (a per-cpu list with seperate locking),
which set the DYING bit.

Fix this race, in __nf_conntrack_confirm(), by removing the CT
from unconfirmed list before checking the DYING bit.  In case
race occured, re-add the CT to the dying list.

While at this, fix coding style of the comment that has been
updated.

Fixes: 93bb0ceb75 ("netfilter: conntrack: remove central spinlock nf_conntrack_lock")
Reported-by: bill bonaparte <programme110@gmail.com>
Signed-off-by: bill bonaparte <programme110@gmail.com>
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
bill bonaparte 2014-11-06 14:36:48 +01:00 • committed by Pablo Neira Ayuso
commit 5195c14c8b
1 changed files with 8 additions and 6 deletions
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14
net/netfilter/nf_conntrack_core.c
View file

@ -611,12 +611,16 @@ __nf_conntrack_confirm(struct sk_buff *skb)
*/
NF_CT_ASSERT(!nf_ct_is_confirmed(ct));
pr_debug("Confirming conntrack %p\n", ct);
/* 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 */
/* We have to check the DYING flag after unlink 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.
*/
nf_ct_del_from_dying_or_unconfirmed_list(ct);
if (unlikely(nf_ct_is_dying(ct))) {
nf_ct_add_to_dying_list(ct);
nf_conntrack_double_unlock(hash, reply_hash);
local_bh_enable();
return NF_ACCEPT;
@ -636,8 +640,6 @@ __nf_conntrack_confirm(struct sk_buff *skb)
zone == nf_ct_zone(nf_ct_tuplehash_to_ctrack(h)))
goto out;
nf_ct_del_from_dying_or_unconfirmed_list(ct);
/* Timer relative to confirmation time, not original
setting time, otherwise we'd get timer wrap in
weird delay cases. */