mptcp: fix retransmission loop when csum is enabled

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@vger.kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@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@kernel.org>

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 5a20ab2789aebb5fd9ac1262e7647815a730890d..7fac5fac20976a260e2efc72f7835dba9a9f0a63 100644 (file)
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -2869,6 +2869,10 @@ 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);