[PATCH net-next v3 4/9] net: tcp: make tcp_rcv_synsent_state_process() return drop reasons

[menglong8.dong@gmail.com]

From: Menglong Dong <imagedong@tencent.com>

The return value of tcp_rcv_synsent_state_process() can be -1, 0 or 1:

- -1: free skb silently
- 0: success and skb is already freed
- 1: drop packet and send a RST

Therefore, we can make it return skb drop reasons instead of '1' on
'reset_and_undo' path, which will not impact the caller.

The new reason 'TCP_PAWSACTIVEREJECTED' is added, which is corresponding
to LINUX_MIB_PAWSACTIVEREJECTED.

Reviewed-by: Jiang Biao <benbjiang@tencent.com>
Reviewed-by: Hao Peng <flyingpeng@tencent.com>
Signed-off-by: Menglong Dong <imagedong@tencent.com>
---
 include/net/dropreason.h | 6 ++++++
 net/ipv4/tcp_input.c     | 7 ++++++-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/include/net/dropreason.h b/include/net/dropreason.h
index 3c6f1e299c35..c60913aba0e9 100644
--- a/include/net/dropreason.h
+++ b/include/net/dropreason.h
@@ -236,6 +236,12 @@ enum skb_drop_reason {
 	 * skb in its receive or send queue are all dropped
 	 */
 	SKB_DROP_REASON_SOCKET_DESTROYED,
+	/**
+	 * @SKB_DROP_REASON_TCP_PAWSACTIVEREJECTED: PAWS check failed for
+	 * active TCP connection, corresponding to
+	 * LINUX_MIB_PAWSACTIVEREJECTED
+	 */
+	SKB_DROP_REASON_TCP_PAWSACTIVEREJECTED,
 	/**
 	 * @SKB_DROP_REASON_MAX: the maximum of drop reason, which shouldn't be
 	 * used as a real 'reason'
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 2e2a9ece9af2..9254f14def43 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -6177,6 +6177,10 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
 				inet_csk_reset_xmit_timer(sk,
 						ICSK_TIME_RETRANS,
 						TCP_TIMEOUT_MIN, TCP_RTO_MAX);
+			if (after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt))
+				SKB_DR_SET(reason, TCP_ACK_UNSENT_DATA);
+			else
+				SKB_DR_SET(reason, TCP_TOO_OLD_ACK);
 			goto reset_and_undo;
 		}
 
@@ -6185,6 +6189,7 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
 			     tcp_time_stamp(tp))) {
 			NET_INC_STATS(sock_net(sk),
 					LINUX_MIB_PAWSACTIVEREJECTED);
+			SKB_DR_SET(reason, TCP_PAWSACTIVEREJECTED);
 			goto reset_and_undo;
 		}
 
@@ -6378,7 +6383,7 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
 reset_and_undo:
 	tcp_clear_options(&tp->rx_opt);
 	tp->rx_opt.mss_clamp = saved_clamp;
-	return 1;
+	return reason;
 }
 
 static void tcp_rcv_synrecv_state_fastopen(struct sock *sk)
-- 
2.36.1