[PATCH net] tcp: Fix error ts_recent time during three-way handshake

[Wang Hai <wanghai38@huawei.com>]

If two ack packets from a connection enter tcp_check_req at the same time
through different cpu, it may happen that req->ts_recent is updated with
with a more recent time and the skb with an older time creates a new sock,
which will cause the tcp_validate_incoming check to fail.

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

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) // failed

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

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Wang Hai <wanghai38@huawei.com>
---
 net/ipv4/tcp_minisocks.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index b089b08e9617..0208455f9eb8 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -878,6 +878,10 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
 	sock_rps_save_rxhash(child, skb);
 	tcp_synack_rtt_meas(child, req);
 	*req_stolen = !own_req;
+	if (own_req && tcp_sk(child)->rx_opt.tstamp_ok &&
+	    unlikely(tcp_sk(child)->rx_opt.ts_recent != tmp_opt.rcv_tsval))
+		tcp_sk(child)->rx_opt.ts_recent = tmp_opt.rcv_tsval;
+
 	return inet_csk_complete_hashdance(sk, child, req, own_req);
 
 listen_overflow:
-- 
2.17.1