[PATCH 3.12 084/127] tcp: fix overflow in __tcp_retransmit_skb()

[Jiri Slaby]

From: Eric Dumazet <edumazet@xxxxxxxxxx>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

[ Upstream commit ffb4d6c8508657824bcef68a36b2a0f9d8c09d10 ]

If a TCP socket gets a large write queue, an overflow can happen
in a test in __tcp_retransmit_skb() preventing all retransmits.

The flow then stalls and resets after timeouts.

Tested:

sysctl -w net.core.wmem_max=1000000000
netperf -H dest -- -s 1000000000

Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
 net/ipv4/tcp_output.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index aa72c9d604a0..f08921156be8 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2336,7 +2336,8 @@ int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb)
 	 * copying overhead: fragmentation, tunneling, mangling etc.
 	 */
 	if (atomic_read(&sk->sk_wmem_alloc) >
-	    min(sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2), sk->sk_sndbuf))
+	    min_t(u32, sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2),
+		  sk->sk_sndbuf))
 		return -EAGAIN;
 
 	if (before(TCP_SKB_CB(skb)->seq, tp->snd_una)) {
-- 
2.10.2