tcp: support rstreason for passive reset

Reuse the dropreason logic to show the exact reason of tcp reset,
so we can finally display the corresponding item in enum sk_reset_reason
instead of reinventing new reset reasons. This patch replaces all
the prior NOT_SPECIFIED reasons.
Signed-off-by: Jason Xing <kernelxing@tencent.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

include/net/rstreason.h

@@ -103,4 +103,19 @@ enum sk_rst_reason {
 	 */
 	SK_RST_REASON_MAX,
 };
+
+/* Convert skb drop reasons to enum sk_rst_reason type */
+static inline enum sk_rst_reason
+sk_rst_convert_drop_reason(enum skb_drop_reason reason)
+{
+	switch (reason) {
+	case SKB_DROP_REASON_NOT_SPECIFIED:
+		return SK_RST_REASON_NOT_SPECIFIED;
+	case SKB_DROP_REASON_NO_SOCKET:
+		return SK_RST_REASON_NO_SOCKET;
+	default:
+		/* If we don't have our own corresponding reason */
+		return SK_RST_REASON_NOT_SPECIFIED;
+	}
+}
 #endif

net/ipv4/tcp_ipv4.c

@@ -1936,7 +1936,7 @@ int tcp_v4_do_rcv(struct sock *sk, struct sk_buff *skb)
 	return 0;
 
 reset:
-	tcp_v4_send_reset(rsk, skb, SK_RST_REASON_NOT_SPECIFIED);
+	tcp_v4_send_reset(rsk, skb, sk_rst_convert_drop_reason(reason));
 discard:
 	kfree_skb_reason(skb, reason);
 	/* Be careful here. If this function gets more complicated and
@@ -2287,7 +2287,10 @@ int tcp_v4_rcv(struct sk_buff *skb)
 		} else {
 			drop_reason = tcp_child_process(sk, nsk, skb);
 			if (drop_reason) {
-				tcp_v4_send_reset(nsk, skb, SK_RST_REASON_NOT_SPECIFIED);
+				enum sk_rst_reason rst_reason;
+
+				rst_reason = sk_rst_convert_drop_reason(drop_reason);
+				tcp_v4_send_reset(nsk, skb, rst_reason);
 				goto discard_and_relse;
 			}
 			sock_put(sk);
@@ -2366,7 +2369,7 @@ int tcp_v4_rcv(struct sk_buff *skb)
 bad_packet:
 		__TCP_INC_STATS(net, TCP_MIB_INERRS);
 	} else {
-		tcp_v4_send_reset(NULL, skb, SK_RST_REASON_NOT_SPECIFIED);
+		tcp_v4_send_reset(NULL, skb, sk_rst_convert_drop_reason(drop_reason));
 	}
 
 discard_it:
@@ -2418,7 +2421,7 @@ int tcp_v4_rcv(struct sk_buff *skb)
 		tcp_v4_timewait_ack(sk, skb);
 		break;
 	case TCP_TW_RST:
-		tcp_v4_send_reset(sk, skb, SK_RST_REASON_NOT_SPECIFIED);
+		tcp_v4_send_reset(sk, skb, sk_rst_convert_drop_reason(drop_reason));
 		inet_twsk_deschedule_put(inet_twsk(sk));
 		goto discard_it;
 	case TCP_TW_SUCCESS:;

net/ipv6/tcp_ipv6.c

@@ -1680,7 +1680,7 @@ int tcp_v6_do_rcv(struct sock *sk, struct sk_buff *skb)
 	return 0;
 
 reset:
-	tcp_v6_send_reset(sk, skb, SK_RST_REASON_NOT_SPECIFIED);
+	tcp_v6_send_reset(sk, skb, sk_rst_convert_drop_reason(reason));
 discard:
 	if (opt_skb)
 		__kfree_skb(opt_skb);
@@ -1865,7 +1865,10 @@ INDIRECT_CALLABLE_SCOPE int tcp_v6_rcv(struct sk_buff *skb)
 		} else {
 			drop_reason = tcp_child_process(sk, nsk, skb);
 			if (drop_reason) {
-				tcp_v6_send_reset(nsk, skb, SK_RST_REASON_NOT_SPECIFIED);
+				enum sk_rst_reason rst_reason;
+
+				rst_reason = sk_rst_convert_drop_reason(drop_reason);
+				tcp_v6_send_reset(nsk, skb, rst_reason);
 				goto discard_and_relse;
 			}
 			sock_put(sk);
@@ -1942,7 +1945,7 @@ INDIRECT_CALLABLE_SCOPE int tcp_v6_rcv(struct sk_buff *skb)
 bad_packet:
 		__TCP_INC_STATS(net, TCP_MIB_INERRS);
 	} else {
-		tcp_v6_send_reset(NULL, skb, SK_RST_REASON_NOT_SPECIFIED);
+		tcp_v6_send_reset(NULL, skb, sk_rst_convert_drop_reason(drop_reason));
 	}
 
 discard_it:
@@ -1998,7 +2001,7 @@ INDIRECT_CALLABLE_SCOPE int tcp_v6_rcv(struct sk_buff *skb)
 		tcp_v6_timewait_ack(sk, skb);
 		break;
 	case TCP_TW_RST:
-		tcp_v6_send_reset(sk, skb, SK_RST_REASON_NOT_SPECIFIED);
+		tcp_v6_send_reset(sk, skb, sk_rst_convert_drop_reason(drop_reason));
 		inet_twsk_deschedule_put(inet_twsk(sk));
 		goto discard_it;
 	case TCP_TW_SUCCESS: