[PATCH 5.10.y] mptcp: ensure snd_una is properly initialized on connect

["Matthieu Baerts (NGI0)" <matttbe@kernel.org>]

From: Paolo Abeni <pabeni@redhat.com>

commit 8031b58c3a9b1db3ef68b3bd749fbee2e1e1aaa3 upstream.

This is strictly related to commit fb7a0d334894 ("mptcp: ensure snd_nxt
is properly initialized on connect"). It turns out that syzkaller can
trigger the retransmit after fallback and before processing any other
incoming packet - so that snd_una is still left uninitialized.

Address the issue explicitly initializing snd_una together with snd_nxt
and write_seq.

Suggested-by: Mat Martineau <martineau@kernel.org>
Fixes: 8fd738049ac3 ("mptcp: fallback in case of simultaneous connect")
Cc: stable@vger.kernel.org
Reported-by: Christoph Paasch <cpaasch@apple.com>
Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/485
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://lore.kernel.org/r/20240607-upstream-net-20240607-misc-fixes-v1-1-1ab9ddfa3d00@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
[ Conflicts in protocol.c, similar to the ones from commit 99951b62bf20
  ("mptcp: ensure snd_nxt is properly initialized on connect"), with the
  same resolution. Note that in this version, 'snd_una' is an atomic64
  type, so use atomic64_set() instead, as it is done everywhere else. ]
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 net/mptcp/protocol.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 36fa456f42ba..a36493bbf895 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -2646,6 +2646,7 @@ static int mptcp_stream_connect(struct socket *sock, struct sockaddr *uaddr,
 		mptcp_subflow_early_fallback(msk, subflow);
 
 	WRITE_ONCE(msk->write_seq, subflow->idsn);
+	atomic64_set(&msk->snd_una, msk->write_seq);
 
 do_connect:
 	err = ssock->ops->connect(ssock, uaddr, addr_len, flags);
-- 
2.43.0