Subject: [PATCH net-next v3 4/7] tcp: rstreason: introduce SK_RST_REASON_TCP_STATE for active reset

From: Jason Xing <[email-masked]>
Date: Thu, 1 Aug 2024 22:54:41 +0800

From: Jason Xing <[email-masked]>

Introducing a new type TCP_STATE to handle some reset conditions
appearing in RFC 793 due to its socket state. Actually, we can look
into RFC 9293 which has no discrepancy about this part.

Signed-off-by: Jason Xing <[email-masked]>
---
v3
Link: https://lore.kernel.org/all/[email-masked]/
1. remove one case from tcp_disconnect, which will be separately
categorized as another reason in the later patch (Eric)

V2
Link: https://lore.kernel.org/all/[email-masked]/
1. use RFC 9293 instead of RFC 793 which is too old (Kuniyuki)
---
 include/net/rstreason.h |  6 ++++++
 net/ipv4/tcp.c          | 10 ++++++----
 net/ipv4/tcp_timer.c    |  2 +-
 3 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/include/net/rstreason.h b/include/net/rstreason.h
index eef658da8952..bbf20d0bbde7 100644
--- a/include/net/rstreason.h
+++ b/include/net/rstreason.h
@@ -20,6 +20,7 @@
 	FN(TCP_ABORT_ON_CLOSE)		\
 	FN(TCP_ABORT_ON_LINGER)		\
 	FN(TCP_ABORT_ON_MEMORY)		\
+	FN(TCP_STATE)			\
 	FN(MPTCP_RST_EUNSPEC)		\
 	FN(MPTCP_RST_EMPTCP)		\
 	FN(MPTCP_RST_ERESOURCE)		\
@@ -102,6 +103,11 @@ enum sk_rst_reason {
 	 * corresponding to LINUX_MIB_TCPABORTONMEMORY
 	 */
 	SK_RST_REASON_TCP_ABORT_ON_MEMORY,
+	/**
+	 * @SK_RST_REASON_TCP_STATE: abort on tcp state
+	 * Please see RFC 9293 for all possible reset conditions
+	 */
+	SK_RST_REASON_TCP_STATE,
 
 	/* Copy from include/uapi/linux/mptcp.h.
 	 * These reset fields will not be changed since they adhere to
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index fd928c447ce8..24777e48bcc8 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -3025,9 +3025,11 @@ int tcp_disconnect(struct sock *sk, int flags)
 		inet_csk_listen_stop(sk);
 	} else if (unlikely(tp->repair)) {
 		WRITE_ONCE(sk->sk_err, ECONNABORTED);
-	} else if (tcp_need_reset(old_state) ||
-		   (tp->snd_nxt != tp->write_seq &&
-		    (1 << old_state) & (TCPF_CLOSING | TCPF_LAST_ACK))) {
+	} else if (tcp_need_reset(old_state)) {
+		tcp_send_active_reset(sk, gfp_any(), SK_RST_REASON_TCP_STATE);
+		WRITE_ONCE(sk->sk_err, ECONNRESET);
+	} else if (tp->snd_nxt != tp->write_seq &&
+		   (1 << old_state) & (TCPF_CLOSING | TCPF_LAST_ACK)) {
 		/* The last check adjusts for discrepancy of Linux wrt. RFC
 		 * states
 		 */
@@ -4649,7 +4651,7 @@ int tcp_abort(struct sock *sk, int err)
 	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);
+					      SK_RST_REASON_TCP_STATE);
 		tcp_done_with_error(sk, err);
 	}
 
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index 0fba4a4fb988..3910f6d8614e 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -779,7 +779,7 @@ static void tcp_keepalive_timer (struct timer_list *t)
 				goto out;
 			}
 		}
-		tcp_send_active_reset(sk, GFP_ATOMIC, SK_RST_REASON_NOT_SPECIFIED);
+		tcp_send_active_reset(sk, GFP_ATOMIC, SK_RST_REASON_TCP_STATE);
 		goto death;
 	}
 
-- 
2.37.3