linux-kernel - [PATCH 3.10 233/319] tcp: fix overflow in __tcp_retransmit

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Date:   Sun,  5 Feb 2017 20:20:55 +0100
From:   Willy Tarreau <w@....eu>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        linux@...ck-us.net
Cc:     Eric Dumazet <edumazet@...gle.com>,
        "David S . Miller" <davem@...emloft.net>, Willy Tarreau <w@....eu>
Subject: [PATCH 3.10 233/319] tcp: fix overflow in __tcp_retransmit_skb()

From: Eric Dumazet <edumazet@...gle.com>

commit ffb4d6c8508657824bcef68a36b2a0f9d8c09d10 upstream.

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@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Willy Tarreau <w@....eu>
---
 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 276b283..465285b 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2327,7 +2327,8 @@ 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)) {
-- 
2.8.0.rc2.1.gbe9624a