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, which also conform to RFC 9293.

At the end of the patch, tcp_write_queue_purge(sk) is removed because it
was already called in tcp_done_with_error().

p.s. This is the same patch with v2. Resent due to mis-labeled "changes
requested" on patchwork.kernel.org.

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@kuroa.me>
Tested-by: Lorenzo Colitti <lorenzo@google.com>
Reviewed-by: Jason Xing <kerneljasonxing@gmail.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20240826102327.1461482-1-kuro@kuroa.me
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index e03a342c9162b65b49551ffdb6302519bc473441..831a18dc7aa6d651dbd86dee8db7d1eb1f824ef5 100644 (file)
--- 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;