[v2.6.34-stable 053/213] net: fix a race in sock_queue_err_skb()

[Paul Gortmaker]

From: Eric Dumazet <eric.dumazet@xxxxxxxxx>

                   -------------------
    This is a commit scheduled for the next v2.6.34 longterm release.
    http://git.kernel.org/?p=linux/kernel/git/paulg/longterm-queue-2.6.34.git
    If you see a problem with using this for longterm, please comment.
                   -------------------

commit 110c43304db6f06490961529536c362d9ac5732f upstream.

As soon as an skb is queued into socket error queue, another thread
can consume it, so we are not allowed to reference skb anymore, or risk
use after free.

Signed-off-by: Eric Dumazet <eric.dumazet@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
[PG: net/core/skbuff.c  -->  include/net/sock.h on 2.6.34 baseline]
Signed-off-by: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
---
 include/net/sock.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/net/sock.h b/include/net/sock.h
index b365fc2597c3..133e350c6fa3 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1428,6 +1428,8 @@ extern int sock_queue_rcv_skb(struct sock *sk, struct sk_buff *skb);
 
 static inline int sock_queue_err_skb(struct sock *sk, struct sk_buff *skb)
 {
+	int len = skb->len;
+
 	/* Cast skb->rcvbuf to unsigned... It's pointless, but reduces
 	   number of warnings when compiling with -W --ANK
 	 */
@@ -1437,7 +1439,7 @@ static inline int sock_queue_err_skb(struct sock *sk, struct sk_buff *skb)
 	skb_set_owner_r(skb, sk);
 	skb_queue_tail(&sk->sk_error_queue, skb);
 	if (!sock_flag(sk, SOCK_DEAD))
-		sk->sk_data_ready(sk, skb->len);
+		sk->sk_data_ready(sk, len);
 	return 0;
 }
 
-- 
1.8.5.2

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