linux-kernel - [PATCH net v2] tcp: Defer ts_recent changes until req is owned

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Message-ID: <20250222103928.12104-1-wanghai38@huawei.com>
Date: Sat, 22 Feb 2025 18:39:28 +0800
From: Wang Hai <wanghai38@...wei.com>
To: <kerneljasonxing@...il.com>, <edumazet@...gle.com>,
	<ncardwell@...gle.com>, <kuniyu@...zon.com>, <davem@...emloft.net>,
	<dsahern@...nel.org>, <kuba@...nel.org>, <pabeni@...hat.com>,
	<horms@...nel.org>, <zhangchangzhong@...wei.com>, <liujian56@...wei.com>,
	<yuehaibing@...wei.com>
CC: <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH net v2] tcp: Defer ts_recent changes until req is owned

The same 5-tuple packet may be processed by different CPUSs, so two
CPUs may receive different ack packets at the same time when the
state is TCP_NEW_SYN_RECV.

In that case, req->ts_recent in tcp_check_req may be changed concurrently,
which will probably cause the newsk's ts_recent to be incorrectly large.
So that tcp_validate_incoming will fail.

cpu1                                    cpu2
tcp_check_req
                                        tcp_check_req
 req->ts_recent = rcv_tsval = t1
                                         req->ts_recent = rcv_tsval = t2

 syn_recv_sock
  newsk->ts_recent = req->ts_recent = t2 // t1 < t2
tcp_child_process
 tcp_rcv_state_process
  tcp_validate_incoming
   tcp_paws_check
    if ((s32)(rx_opt->ts_recent - rx_opt->rcv_tsval) <= paws_win)
	// t2 - t1 > paws_win, failed

In tcp_check_req, Defer ts_recent changes to this skb's to fix this bug.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Wang Hai <wanghai38@...wei.com>
---
v1->v2: Modified the fix logic based on Eric's suggestion. Also modified the msg
 net/ipv4/tcp_minisocks.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index b089b08e9617..53700206f498 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -815,12 +815,6 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
 
 	/* In sequence, PAWS is OK. */
 
-	/* TODO: We probably should defer ts_recent change once
-	 * we take ownership of @req.
-	 */
-	if (tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt))
-		WRITE_ONCE(req->ts_recent, tmp_opt.rcv_tsval);
-
 	if (TCP_SKB_CB(skb)->seq == tcp_rsk(req)->rcv_isn) {
 		/* Truncate SYN, it is out of window starting
 		   at tcp_rsk(req)->rcv_isn + 1. */
@@ -869,6 +863,9 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
 	if (!child)
 		goto listen_overflow;
 
+	if (own_req && tmp_opt.saw_tstamp && !after(TCP_SKB_CB(skb)->seq, tcp_rsk(req)->rcv_nxt))
+		tcp_sk(child)->rx_opt.ts_recent = tmp_opt.rcv_tsval;
+
 	if (own_req && rsk_drop_req(req)) {
 		reqsk_queue_removed(&inet_csk(req->rsk_listener)->icsk_accept_queue, req);
 		inet_csk_reqsk_queue_drop_and_put(req->rsk_listener, req);
-- 
2.17.1