CVE-2013-4129: Improper Input Validation (CWE-20)
value: The bridge multicast implementation in the Linux kernel through 3.10.3 does not check whether a certain timer is armed before modifying the timeout value of that timer, which allows local users to cause a denial of service (BUG and system crash) via vectors involving the shutdown of a KVM virtual machine, related to net/bridge/br_mdb.c and net/bridge/br_multicast.c.
CWE description: The product receives input or data, but it does
        not validate or incorrectly validates that the input has the
        properties that are required to process the data safely and
        correctly.
Published: 2013-07-29T13:59Z
Repository: https://github.com/torvalds/linux
Language: C
Files changed: net/bridge/br_mdb.c, net/bridge/br_multicast.c
Commit date: 2013-07-06 18:12:47 -0700
Commit message: bridge: fix some kernel warning in multicast timer

Several people reported the warning: "kernel BUG at kernel/timer.c:729!"
and the stack trace is:

	#7 [ffff880214d25c10] mod_timer+501 at ffffffff8106d905
	#8 [ffff880214d25c50] br_multicast_del_pg.isra.20+261 at ffffffffa0731d25 [bridge]
	#9 [ffff880214d25c80] br_multicast_disable_port+88 at ffffffffa0732948 [bridge]
	#10 [ffff880214d25cb0] br_stp_disable_port+154 at ffffffffa072bcca [bridge]
	#11 [ffff880214d25ce8] br_device_event+520 at ffffffffa072a4e8 [bridge]
	#12 [ffff880214d25d18] notifier_call_chain+76 at ffffffff8164aafc
	#13 [ffff880214d25d50] raw_notifier_call_chain+22 at ffffffff810858f6
	#14 [ffff880214d25d60] call_netdevice_notifiers+45 at ffffffff81536aad
	#15 [ffff880214d25d80] dev_close_many+183 at ffffffff81536d17
	#16 [ffff880214d25dc0] rollback_registered_many+168 at ffffffff81537f68
	#17 [ffff880214d25de8] rollback_registered+49 at ffffffff81538101
	#18 [ffff880214d25e10] unregister_netdevice_queue+72 at ffffffff815390d8
	#19 [ffff880214d25e30] __tun_detach+272 at ffffffffa074c2f0 [tun]
	#20 [ffff880214d25e88] tun_chr_close+45 at ffffffffa074c4bd [tun]
	#21 [ffff880214d25ea8] __fput+225 at ffffffff8119b1f1
	#22 [ffff880214d25ef0] ____fput+14 at ffffffff8119b3fe
	#23 [ffff880214d25f00] task_work_run+159 at ffffffff8107cf7f
	#24 [ffff880214d25f30] do_notify_resume+97 at ffffffff810139e1
	#25 [ffff880214d25f50] int_signal+18 at ffffffff8164f292

this is due to I forgot to check if mp->timer is armed in
br_multicast_del_pg(). This bug is introduced by
commit 9f00b2e7cf241fa389733d41b6 (bridge: only expire the mdb entry
when query is received).

Same for __br_mdb_del().

Tested-by: poma <pomidorabelisima@gmail.com>
Reported-by: LiYonghua <809674045@qq.com>
Reported-by: Robert Hancock <hancockrwd@gmail.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Stephen Hemminger <stephen@networkplumber.org>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Cong Wang <amwang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Diff: diff --git a/net/bridge/br_mdb.c b/net/bridge/br_mdb.c
index 19942e38fd2d93..0daae3ec235554 100644
--- a/net/bridge/br_mdb.c
+++ b/net/bridge/br_mdb.c
@@ -445,11 +445,11 @@ static int __br_mdb_del(struct net_bridge *br, struct br_mdb_entry *entry)
 		hlist_del_init(&p->mglist);
 		del_timer(&p->timer);
 		call_rcu_bh(&p->rcu, br_multicast_free_pg);
 		err = 0;
 
-		if (!mp->ports && !mp->mglist &&
+		if (!mp->ports && !mp->mglist && mp->timer_armed &&
 		    netif_running(br->dev))
 			mod_timer(&mp->timer, jiffies);
 		break;
 	}
 
diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index 81befac015e175..69af490cce4437 100644
--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -268,11 +268,11 @@ static void br_multicast_del_pg(struct net_bridge *br,
 		rcu_assign_pointer(*pp, p->next);
 		hlist_del_init(&p->mglist);
 		del_timer(&p->timer);
 		call_rcu_bh(&p->rcu, br_multicast_free_pg);
 
-		if (!mp->ports && !mp->mglist &&
+		if (!mp->ports && !mp->mglist && mp->timer_armed &&
 		    netif_running(br->dev))
 			mod_timer(&mp->timer, jiffies);
 
 		return;
 	}

Vulnerable code: 		if (!mp->ports && !mp->mglist &&
		if (!mp->ports && !mp->mglist &&
Fixed code: 		if (!mp->ports && !mp->mglist && mp->timer_armed &&
		if (!mp->ports && !mp->mglist && mp->timer_armed &&