[PATCH net] tcp: allow MSG_ZEROCOPY transmission also in CLOSE_WAIT state

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

From: Willem de Bruijn <willemb@google.com>

TCP transmission with MSG_ZEROCOPY fails if the peer closes its end of
the connection and so transitions this socket to CLOSE_WAIT state.

Transmission in close wait state is acceptable. Other similar tests in
the stack (e.g., in FastOpen) accept both states. Relax this test, too.

Link: https://www.mail-archive.com/netdev@vger.kernel.org/msg276886.html
Link: https://www.mail-archive.com/netdev@vger.kernel.org/msg227390.html
Fixes: f214f915e7db ("tcp: enable MSG_ZEROCOPY")
Reported-by: Marek Majkowski <marek@cloudflare.com>
Signed-off-by: Willem de Bruijn <willemb@google.com>
CC: Yuchung Cheng <ycheng@google.com>
CC: Neal Cardwell <ncardwell@google.com>
CC: Soheil Hassas Yeganeh <soheil@google.com>
CC: Alexey Kodanev <alexey.kodanev@oracle.com>
---

This is a narrow fix. Alexey Kodanev suggested a while ago that the
entire check might be removed, also opening up more cases for zerocopy
with fastopen. For net-next, I will take another look at that and also
at adding a tcp_data_sending_states() helper to avoid open coding this
test everywhere.
---
 net/ipv4/tcp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 27e2f6837062..2079145a3b7c 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1186,7 +1186,7 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
 	flags = msg->msg_flags;
 
 	if (flags & MSG_ZEROCOPY && size && sock_flag(sk, SOCK_ZEROCOPY)) {
-		if (sk->sk_state != TCP_ESTABLISHED) {
+		if ((1 << sk->sk_state) & ~(TCPF_ESTABLISHED | TCPF_CLOSE_WAIT)) {
 			err = -EINVAL;
 			goto out_err;
 		}
-- 
2.20.1.97.g81188d93c3-goog