linux-kernel - [PATCH 4.4 1/1] tcp: refine memory limit test in tcp

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Date:   Wed, 26 Jun 2019 16:45:05 +0800
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
        Christoph Paasch <cpaasch@...le.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.4 1/1] tcp: refine memory limit test in tcp_fragment()

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

commit b6653b3629e5b88202be3c9abc44713973f5c4b4 upstream.

tcp_fragment() might be called for skbs in the write queue.

Memory limits might have been exceeded because tcp_sendmsg() only
checks limits at full skb (64KB) boundaries.

Therefore, we need to make sure tcp_fragment() wont punish applications
that might have setup very low SO_SNDBUF values.

Fixes: f070ef2ac667 ("tcp: tcp_fragment() should apply sane memory limits")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Reported-by: Christoph Paasch <cpaasch@...le.com>
Tested-by: Christoph Paasch <cpaasch@...le.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 net/ipv4/tcp_output.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1161,7 +1161,7 @@ int tcp_fragment(struct sock *sk, struct
 	if (nsize < 0)
 		nsize = 0;

-	if (unlikely((sk->sk_wmem_queued >> 1) > sk->sk_sndbuf)) {
+	if (unlikely((sk->sk_wmem_queued >> 1) > sk->sk_sndbuf + 0x20000)) {
 		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPWQUEUETOOBIG);
 		return -ENOMEM;
 	}