[PATCH net-next] tcp: tcp_data_ready() must look at SOCK_DONE

From: Eric Dumazet <edumazet@google.com>

My prior cleanup missed that tcp_data_ready() has to look at SOCK_DONE.
Otherwise, an application using SO_RCVLOWAT will not get EPOLLIN event
if a FIN is received in the middle of expected payload.

The reason SOCK_DONE is not examined in tcp_epollin_ready()
is that tcp_poll() catches the FIN because tcp_fin()
is also setting RCV_SHUTDOWN into sk->sk_shutdown

Fixes: 05dc72aba364 ("tcp: factorize logic into tcp_epollin_ready()")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Wei Wang <redacted>
Cc: Arjun Roy <redacted>
---
 net/ipv4/tcp_input.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index e32a7056cb7640c67ef2d6a4d9484684d2602fcd..69a545db80d2ead47ffcf2f3819a6d066e95f35d 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c

@@ -4924,7 +4924,7 @@ int tcp_send_rcvq(struct sock *sk, struct msghdr *msg, size_t size)
 
 void tcp_data_ready(struct sock *sk)
 {
-	if (tcp_epollin_ready(sk, sk->sk_rcvlowat))
+	if (tcp_epollin_ready(sk, sk->sk_rcvlowat) || sock_flag(sk, SOCK_DONE))
 		sk->sk_data_ready(sk);
 }
 

-- 
2.30.0.478.g8a0d178c01-goog

On Sat, Feb 13, 2021 at 6:26 AM Eric Dumazet [off-list ref] wrote:

From: Eric Dumazet <edumazet@google.com>

My prior cleanup missed that tcp_data_ready() has to look at SOCK_DONE.
Otherwise, an application using SO_RCVLOWAT will not get EPOLLIN event
if a FIN is received in the middle of expected payload.

The reason SOCK_DONE is not examined in tcp_epollin_ready()
is that tcp_poll() catches the FIN because tcp_fin()
is also setting RCV_SHUTDOWN into sk->sk_shutdown

Fixes: 05dc72aba364 ("tcp: factorize logic into tcp_epollin_ready()")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Wei Wang <redacted>
Cc: Arjun Roy <redacted>
---

Thanks Eric for the fix!

Reviewed-by: Wei Wang <redacted>

Hello:

This patch was applied to netdev/net-next.git (refs/heads/master):

On Sat, 13 Feb 2021 06:26:34 -0800 you wrote:

From: Eric Dumazet <edumazet@google.com>

My prior cleanup missed that tcp_data_ready() has to look at SOCK_DONE.
Otherwise, an application using SO_RCVLOWAT will not get EPOLLIN event
if a FIN is received in the middle of expected payload.

The reason SOCK_DONE is not examined in tcp_epollin_ready()
is that tcp_poll() catches the FIN because tcp_fin()
is also setting RCV_SHUTDOWN into sk->sk_shutdown

[...]

Here is the summary with links:
  - [net-next] tcp: tcp_data_ready() must look at SOCK_DONE
    https://git.kernel.org/netdev/net-next/c/39354eb29f59

You are awesome, thank you!
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