[PATCH net-next-2.6] xt_hashlimit: fix locking

Eric Dumazet
2010-02-17T16:43:47Z

Le mardi 16 février 2010 à 15:55 +0100, Patrick McHardy a écrit :
> commit 2eff25c18c3d332d3c4dd98f2ac9b7114e9771b0
> Author: Patrick McHardy <kaber@trash.net>
> Date: Wed Feb 3 13:24:54 2010 +0100
>
> netfilter: xt_hashlimit: fix race condition and simplify locking
>
> As noticed by Shin Hong <hongshin@gmail.com>, there is a race between
> htable_find_get() and htable_put():
>
> htable_put(): htable_find_get():
>
> spin_lock_bh(&hashlimit_lock);
> <search entry>
> atomic_dec_and_test(&hinfo->use)
> atomic_inc(&hinfo->use)
> spin_unlock_bh(&hashlimit_lock)
> return hinfo;
> spin_lock_bh(&hashlimit_lock);
> hlist_del(&hinfo->node);
> spin_unlock_bh(&hashlimit_lock);
> htable_destroy(hinfo);
>
> The entire locking concept is overly complicated, tables are only
> created/referenced and released in process context, so a single
> mutex works just fine. Remove the hashinfo_spinlock and atomic
> reference count and use the mutex to protect table lookups/creation
> and reference count changes.
>
> Signed-off-by: Patrick McHardy <kaber@trash.net>
>

Patrick, David

I believe this patch has a problem, since latest net-next-2.6 triggers :

[ 240.682047] INFO: task iptables:4512 blocked for more than 120
seconds.
[ 240.682125] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
disables this message.
[ 240.682198] iptables D f7a69c48 0 4512 4436 0x00000000
[ 240.682201] f7a69c5c 00000086 00000002 f7a69c48 c3603304 00000000
c0379b0d 0000000e
[ 240.682540] 00000138 f8c06504 fffbef49 d15abc2a 00000007 c0785000
c0788304 00000000
[ 240.682861] f81af0c0 c078d080 d157e120 00000007 f81aee40 c037a608
00000202 f9e38478
[ 240.683191] Call Trace:
[ 240.683247] [<c0379b0d>] ? get_from_free_list+0x3d/0x50
[ 240.683303] [<c037a608>] ? ida_pre_get+0x18/0xe0
[ 240.683359] [<c05503ed>] __mutex_lock_slowpath+0xed/0x230
[ 240.683426] [<c0550540>] mutex_lock+0x10/0x20
[ 240.683488] [<c04dee7e>] hashlimit_mt_check+0x29e/0x380
[ 240.683544] [<c04de02c>] xt_check_match+0x9c/0x1b0
[ 240.683599] [<c05509a7>] ? __mutex_lock_interruptible_slowpath
+0x1a7/0x260
[ 240.683657] [<c05509a7>] ? __mutex_lock_interruptible_slowpath
+0x1a7/0x260
[ 240.683716] [<c05502fd>] ? mutex_unlock+0xd/0x10
[ 240.683770] [<c04ddb1f>] ? xt_find_match+0xdf/0x150
[ 240.683831] [<c0521994>] translate_table+0x384/0x760
[ 240.683886] [<c04dde02>] ? xt_alloc_table_info+0x52/0xc0
[ 240.683942] [<c0522bef>] do_ipt_set_ctl+0x16f/0x440
[ 240.683998] [<c04da2cb>] nf_sockopt+0x15b/0x1a0
[ 240.684062] [<c0551ca0>] ? _raw_spin_lock_bh+0x10/0x30
[ 240.684118] [<c04da369>] nf_setsockopt+0x29/0x30
[ 240.684177] [<c04eb96e>] ip_setsockopt+0x8e/0xa0
[ 240.684233] [<c02bd6ec>] ? page_add_new_anon_rmap+0x7c/0x90
[ 240.684289] [<c0504df4>] raw_setsockopt+0x44/0x80
[ 240.684345] [<c04aaf87>] sock_common_setsockopt+0x27/0x30
[ 240.684411] [<c04a9569>] sys_setsockopt+0x59/0xb0
[ 240.684472] [<c04aa90a>] sys_socketcall+0x12a/0x280
[ 240.684528] [<c0202c50>] sysenter_do_call+0x12/0x26

htable_create() is called with hashlimit_mutex already hold

Maybe original race could be solved using atomic_inc_not_zero() instead
of atomic_inc() ?

Or following quick & dirty patch just cures the problem.

Thanks

[PATCH net-next-2.6] xt_hashlimit: fix locking

Commit 2eff25c18c3d332d3c4dd98f2ac9b7114e9771b0
(netfilter: xt_hashlimit: fix race condition and simplify locking)
added a mutex deadlock :
htable_create() is called with hashlimit_mutex already locked

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>

diff --git a/net/netfilter/xt_hashlimit.c b/net/netfilter/xt_hashlimit.c
index e47fb80..d952806 100644
--- a/net/netfilter/xt_hashlimit.c
+++ b/net/netfilter/xt_hashlimit.c
@@ -262,9 +262,7 @@ static int htable_create_v0(struct net *net, struct xt_hashlimit_info *minfo, u_
hinfo->timer.expires = jiffies + msecs_to_jiffies(hinfo->cfg.gc_interval);
add_timer(&hinfo->timer);

- mutex_lock(&hashlimit_mutex);
hlist_add_head(&hinfo->node, &hashlimit_net->htables);
- mutex_unlock(&hashlimit_mutex);

return 0;
}
@@ -327,9 +325,7 @@ static int htable_create(struct net *net, struct xt_hashlimit_mtinfo1 *minfo,
hinfo->timer.expires = jiffies + msecs_to_jiffies(hinfo->cfg.gc_interval);
add_timer(&hinfo->timer);

- mutex_lock(&hashlimit_mutex);
hlist_add_head(&hinfo->node, &hashlimit_net->htables);
- mutex_unlock(&hashlimit_mutex);

return 0;
}

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