[PATCH net] tcp: refine memory limit test in tcp_fragment()

[Eric Dumazet]

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 <eduma...@google.com>
Reported-by: Christoph Paasch <cpaa...@apple.com>
---
 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 
00c01a01b547ec67c971dc25a74c9258563cf871..0ebc33d1c9e5099d163a234930e213ee35e9fbd1
 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1296,7 +1296,8 @@ int tcp_fragment(struct sock *sk, enum tcp_queue 
tcp_queue,
        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 &&
+                    tcp_queue != TCP_FRAG_IN_WRITE_QUEUE)) {
                NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPWQUEUETOOBIG);
                return -ENOMEM;
        }
-- 
2.22.0.410.gd8fdbe21b5-goog