[PATCH 2/4] tcp: refine memory limit test in tcp_fragment()

[Tyler Hicks]

From: Eric Dumazet <edumazet at google.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 at google.com>
Reported-by: Christoph Paasch <cpaasch at apple.com>
Tested-by: Christoph Paasch <cpaasch at apple.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>

CVE-2019-11478

(cherry picked from commit 46c7b5d6f2a51c355b29118814fbfbdb79c35656 linux-stable)
Signed-off-by: Tyler Hicks <tyhicks at canonical.com>
---
 net/ipv4/tcp_output.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index ede265fbf7ba..1b2a6ab5da9d 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1163,7 +1163,7 @@ int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
 	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;
 	}
-- 
2.17.1