netdev - [PATCH v3] netfilter: ipset: Fix sleeping memory allocation in atomic context

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Date:	Fri, 16 Oct 2015 09:40:28 +0300
From:	Nikolay Borisov <kernel@...p.com>
To:	kadlec@...ckhole.kfki.hu, eric.dumazet@...il.com
Cc:	netfilter-devel@...r.kernel.org, pablo@...filter.org,
	davem@...emloft.net, netdev@...r.kernel.org,
	operations@...eground.com
Subject: [PATCH v3] netfilter: ipset: Fix sleeping memory allocation in atomic context

Commit 00590fdd5be0 introduced RCU locking in list type and in
doing so introduced a memory allocation in list_set_add, which 
is done in an atomic context, due to the fact that ipset rcu 
list modifications are serialised with a spin lock. The reason 
why we can't use a mutex is that in addition to modifying the 
list with ipset commands, it's also being modified when a
particular ipset rule timeout expires aka garbage collection. 
This gc is triggered from set_cleanup_entries, which in turn 
is invoked from a timer thus requiring the lock to be bh-safe. 

Concretely the following call chain can lead to "sleeping function
called in atomic context" splat: 
call_ad -> list_set_uadt -> list_set_uadd -> kzalloc(, GFP_KERNEL).
And since GFP_KERNEL allows initiating direct reclaim thus
potentially sleeping in the allocation path.

To fix the issue change the allocation type to GFP_ATOMIC, to
correctly reflect that it is occuring in an atomic context.

Fixes: 00590fdd5be0 ("netfilter: ipset: Introduce RCU locking in list type")

Acked-by: Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>
Signed-off-by: Nikolay Borisov <kernel@...p.com>
---

Changes since v2:
 * Massaged the changelog to reflect discussion 
 on the mailing list

Changes since v1: 
 * Added acked-by 
 * Fixed patch header

 net/netfilter/ipset/ip_set_list_set.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/netfilter/ipset/ip_set_list_set.c b/net/netfilter/ipset/ip_set_list_set.c
index a1fe537..5a30ce6 100644
--- a/net/netfilter/ipset/ip_set_list_set.c
+++ b/net/netfilter/ipset/ip_set_list_set.c
@@ -297,7 +297,7 @@ list_set_uadd(struct ip_set *set, void *value, const struct ip_set_ext *ext,
 	      ip_set_timeout_expired(ext_timeout(n, set))))
 		n =  NULL;

-	e = kzalloc(set->dsize, GFP_KERNEL);
+	e = kzalloc(set->dsize, GFP_ATOMIC);
 	if (!e)
 		return -ENOMEM;
 	e->id = d->id;
-- 
2.5.0

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