This is a note to let you know that I've just added the patch titled
netfilter: conntrack: fix race between confirmation and flush
to the 3.18-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
netfilter-conntrack-fix-race-between-confirmation-and-flush.patch
and it can be found in the queue-3.18 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From 8ca3f5e974f2b4b7f711589f4abff920db36637a Mon Sep 17 00:00:00 2001
From: Pablo Neira Ayuso <[email protected]>
Date: Tue, 25 Nov 2014 00:14:47 +0100
Subject: netfilter: conntrack: fix race between confirmation and flush
From: Pablo Neira Ayuso <[email protected]>
commit 8ca3f5e974f2b4b7f711589f4abff920db36637a upstream.
Commit 5195c14c8b27c ("netfilter: conntrack: fix race in
__nf_conntrack_confirm against get_next_corpse") aimed to resolve the
race condition between the confirmation (packet path) and the flush
command (from control plane). However, it introduced a crash when
several packets race to add a new conntrack, which seems easier to
reproduce when nf_queue is in place.
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
This patch also changes the verdict from NF_ACCEPT to NF_DROP when
we lose race. Basically, the confirmation happens for the first packet
that we see in a flow. If you just invoked conntrack -F once (which
should be the common case), then this is likely to be the first packet
of the flow (unless you already called flush anytime soon in the past).
This should be hard to trigger, but better drop this packet, otherwise
we leave things in inconsistent state since the destination will likely
reply to this packet, but it will find no conntrack, unless the origin
retransmits.
The change of the verdict has been discussed in:
https://www.marc.info/?l=linux-netdev&m=141588039530056&w=2
Signed-off-by: Pablo Neira Ayuso <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
net/netfilter/nf_conntrack_core.c | 22 ++++++++++------------
1 file changed, 10 insertions(+), 12 deletions(-)
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -611,16 +611,15 @@ __nf_conntrack_confirm(struct sk_buff *s
*/
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 */
-
- if (unlikely(nf_ct_is_dying(ct))) {
- nf_conntrack_double_unlock(hash, reply_hash);
- local_bh_enable();
- return NF_ACCEPT;
- }
+ /* 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)))
+ goto out;
/* See if there's one in the list already, including reverse:
NAT could have grabbed it without realizing, since we're
@@ -636,8 +635,6 @@ __nf_conntrack_confirm(struct sk_buff *s
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. */
@@ -673,6 +670,7 @@ __nf_conntrack_confirm(struct sk_buff *s
return NF_ACCEPT;
out:
+ nf_ct_add_to_dying_list(ct);
nf_conntrack_double_unlock(hash, reply_hash);
NF_CT_STAT_INC(net, insert_failed);
local_bh_enable();
Patches currently in stable-queue which might be from [email protected] are
queue-3.18/netfilter-nfnetlink-validate-nfnetlink-header-from-batch.patch
queue-3.18/netfilter-nf_tables-fix-flush-ruleset-chain-dependencies.patch
queue-3.18/netfilter-nfnetlink-relax-strict-multicast-group-check-from-netlink_bind.patch
queue-3.18/netfilter-conntrack-fix-race-between-confirmation-and-flush.patch
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