[Devel] [PATCH hci-8.1 1/8] ms/mptcp: fix retransmission loop when csum is enabled

[Eva Kurchatova]

From: Paolo Abeni <pabeni at redhat.com>

Sashiko noted that retransmission with csum enabled can actually
transmit new data, but currently the relevant code does not update
accordingly snd_nxt.

The may cause incoming ack drop and an endless retransmission loop.

Address the issue incrementing snd_nxt as needed.

Fixes: 4e14867d5e91 ("mptcp: tune re-injections for csum enabled mode")
Cc: stable at vger.kernel.org
Signed-off-by: Paolo Abeni <pabeni at redhat.com>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe at kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe at kernel.org>
Link: https://patch.msgid.link/20260602-net-mptcp-misc-fixes-7-1-rc7-v2-2-856831229976@kernel.org
Signed-off-by: Jakub Kicinski <kuba at kernel.org>
(cherry picked from commit d1918b36edcaed0ec4ef6888b2358c6b1ddcff47)

https://virtuozzo.atlassian.net/browse/VSTOR-153491
Feature: fix ms/net
Signed-off-by: Eva Kurchatova <eva.kurchatova at virtuozzo.com>
---
 net/mptcp/protocol.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index e526648a583e..9f1cc648a272 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -2666,6 +2666,10 @@ static void __mptcp_retrans(struct sock *sk)
 	msk->bytes_retrans += len;
 	dfrag->already_sent = max(dfrag->already_sent, len);
 
+	/* With csum enabled retransmission can send new data. */
+	if (after64(dfrag->already_sent + dfrag->data_seq, msk->snd_nxt))
+		WRITE_ONCE(msk->snd_nxt, dfrag->already_sent + dfrag->data_seq);
+
 reset_timer:
 	mptcp_check_and_set_pending(sk);
 
-- 
2.56.0