netdev - [PATCH net,v2] tcp: fix forever orphan socket caused by tcp

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Message-Id: <20240812105315.440718-1-kuro@kuroa.me>
Date: Mon, 12 Aug 2024 18:53:15 +0800
From: Xueming Feng <kuro@...oa.me>
To: "David S . Miller" <davem@...emloft.net>,
	netdev@...r.kernel.org,
	Eric Dumazet <edumazet@...gle.com>,
	Lorenzo Colitti <lorenzo@...gle.com>,
	Jason Xing <kerneljasonxing@...il.com>
Cc: Neal Cardwell <ncardwell@...gle.com>,
	Yuchung Cheng <ycheng@...gle.com>,
	Soheil Hassas Yeganeh <soheil@...gle.com>,
	David Ahern <dsahern@...nel.org>,
	linux-kernel@...r.kernel.org,
	Xueming Feng <kuro@...oa.me>
Subject: [PATCH net,v2] tcp: fix forever orphan socket caused by tcp_abort

We have some problem closing zero-window fin-wait-1 tcp sockets in our 
environment. This patch come from the investigation.

Previously tcp_abort only sends out reset and calls tcp_done when the 
socket is not SOCK_DEAD, aka orphan. For orphan socket, it will only 
purging the write queue, but not close the socket and left it to the 
timer.

While purging the write queue, tp->packets_out and sk->sk_write_queue 
is cleared along the way. However tcp_retransmit_timer have early 
return based on !tp->packets_out and tcp_probe_timer have early 
return based on !sk->sk_write_queue.

This caused ICSK_TIME_RETRANS and ICSK_TIME_PROBE0 not being resched 
and socket not being killed by the timers, converting a zero-windowed
orphan into a forever orphan.

This patch removes the SOCK_DEAD check in tcp_abort, making it send 
reset to peer and close the socket accordingly. Preventing the 
timer-less orphan from happening.

According to Lorenzo's email in the v1 thread, the check was there to
prevent force-closing the same socket twice. That situation is handled
by testing for TCP_CLOSE inside lock, and returning -ENOENT if it is
already closed.

The -ENOENT code comes from the associate patch Lorenzo made for 
iproute2-ss; link attached below.

Link: https://patchwork.ozlabs.org/project/netdev/patch/1450773094-7978-3-git-send-email-lorenzo@google.com/
Fixes: c1e64e298b8c ("net: diag: Support destroying TCP sockets.")
Signed-off-by: Xueming Feng <kuro@...oa.me>
---
 net/ipv4/tcp.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index e03a342c9162..831a18dc7aa6 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -4637,6 +4637,13 @@ int tcp_abort(struct sock *sk, int err)
 		/* Don't race with userspace socket closes such as tcp_close. */
 		lock_sock(sk);

+	/* Avoid closing the same socket twice. */
+	if (sk->sk_state == TCP_CLOSE) {
+		if (!has_current_bpf_ctx())
+			release_sock(sk);
+		return -ENOENT;
+	}
+
 	if (sk->sk_state == TCP_LISTEN) {
 		tcp_set_state(sk, TCP_CLOSE);
 		inet_csk_listen_stop(sk);
@@ -4646,16 +4653,13 @@ int tcp_abort(struct sock *sk, int err)
 	local_bh_disable();
 	bh_lock_sock(sk);

-	if (!sock_flag(sk, SOCK_DEAD)) {
-		if (tcp_need_reset(sk->sk_state))
-			tcp_send_active_reset(sk, GFP_ATOMIC,
-					      SK_RST_REASON_NOT_SPECIFIED);
-		tcp_done_with_error(sk, err);
-	}
+	if (tcp_need_reset(sk->sk_state))
+		tcp_send_active_reset(sk, GFP_ATOMIC,
+				      SK_RST_REASON_NOT_SPECIFIED);
+	tcp_done_with_error(sk, err);

 	bh_unlock_sock(sk);
 	local_bh_enable();
-	tcp_write_queue_purge(sk);
 	if (!has_current_bpf_ctx())
 		release_sock(sk);
 	return 0;
--