linux-kernel - [PATCH net-next 5/9] net: tcp: make tcp_rcv_synsent_state

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Date:   Mon, 16 May 2022 11:45:15 +0800
From:   menglong8.dong@...il.com
To:     edumazet@...gle.com
Cc:     rostedt@...dmis.org, mingo@...hat.com, davem@...emloft.net,
        yoshfuji@...ux-ipv6.org, dsahern@...nel.org, kuba@...nel.org,
        pabeni@...hat.com, imagedong@...cent.com, kafai@...com,
        talalahmad@...gle.com, keescook@...omium.org,
        dongli.zhang@...cle.com, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org
Subject: [PATCH net-next 5/9] net: tcp: make tcp_rcv_synsent_state_process() return drop reasons

From: Menglong Dong <imagedong@...cent.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 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.

Signed-off-by: Menglong Dong <imagedong@...cent.com>
---
 include/linux/skbuff.h | 1 +
 net/ipv4/tcp_input.c   | 7 ++++++-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 3c7b1e9aabbb..36e0971f4cc9 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -619,6 +619,7 @@ struct sk_buff;
 	FN(IP_INNOROUTES)		\
 	FN(PKT_TOO_BIG)			\
 	FN(SOCKET_DESTROYED)		\
+	FN(TCP_PAWSACTIVEREJECTED)	\
 	FN(MAX)
 
 /* The reason of skb drop, which is used in kfree_skb_reason().
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 97cfcd85f84e..e8d26a68bc45 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -6174,6 +6174,10 @@ 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;
 		}
 
@@ -6182,6 +6186,7 @@ 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;
 		}
 
@@ -6375,7 +6380,7 @@ 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