[ 3.5.y.z extended stable ] Patch "net: fix infinite loop in __skb_recv_datagram()" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    net: fix infinite loop in __skb_recv_datagram()

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 260163e6c1697d93887a19c357e5a92756a4e784 Mon Sep 17 00:00:00 2001
From: Eric Dumazet <edumazet at google.com>
Date: Tue, 12 Feb 2013 06:16:53 +0000
Subject: [PATCH] net: fix infinite loop in __skb_recv_datagram()

commit 77c1090f94d1b0b5186fb13a1b71b47b1343f87f upstream.

Tommi was fuzzing with trinity and reported the following problem :

commit 3f518bf745 (datagram: Add offset argument to __skb_recv_datagram)
missed that a raw socket receive queue can contain skbs with no payload.

We can loop in __skb_recv_datagram() with MSG_PEEK mode, because
wait_for_packet() is not prepared to skip these skbs.

[   83.541011] INFO: rcu_sched detected stalls on CPUs/tasks: {}
(detected by 0, t=26002 jiffies, g=27673, c=27672, q=75)
[   83.541011] INFO: Stall ended before state dump start
[  108.067010] BUG: soft lockup - CPU#0 stuck for 22s! [trinity-child31:2847]
...
[  108.067010] Call Trace:
[  108.067010]  [<ffffffff818cc103>] __skb_recv_datagram+0x1a3/0x3b0
[  108.067010]  [<ffffffff818cc33d>] skb_recv_datagram+0x2d/0x30
[  108.067010]  [<ffffffff819ed43d>] rawv6_recvmsg+0xad/0x240
[  108.067010]  [<ffffffff818c4b04>] sock_common_recvmsg+0x34/0x50
[  108.067010]  [<ffffffff818bc8ec>] sock_recvmsg+0xbc/0xf0
[  108.067010]  [<ffffffff818bf31e>] sys_recvfrom+0xde/0x150
[  108.067010]  [<ffffffff81ca4329>] system_call_fastpath+0x16/0x1b

Reported-by: Tommi Rantala <tt.rantala at gmail.com>
Tested-by: Tommi Rantala <tt.rantala at gmail.com>
Signed-off-by: Eric Dumazet <edumazet at google.com>
Cc: Pavel Emelyanov <xemul at parallels.com>
Acked-by: Pavel Emelyanov <xemul at parallels.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 net/core/datagram.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/datagram.c b/net/core/datagram.c
index ae6acf6..064151a 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -187,7 +187,7 @@ struct sk_buff *__skb_recv_datagram(struct sock *sk, unsigned int flags,
 		skb_queue_walk(queue, skb) {
 			*peeked = skb->peeked;
 			if (flags & MSG_PEEK) {
-				if (*off >= skb->len) {
+				if (*off >= skb->len && skb->len) {
 					*off -= skb->len;
 					continue;
 				}
--
1.8.1.2