mptcp: ensure snd_una is properly initialized on connect

mainline inclusion
from mainline-v6.10-rc4
commit 8031b58c3a9b1db3ef68b3bd749fbee2e1e1aaa3
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/IACQHR
CVE: CVE-2024-40931

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=8031b58c3a9b1db3ef68b3bd749fbee2e1e1aaa3



--------------------------------

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: 8fd73804 ("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:
	net/mptcp/protocol.c
[The conflict occurs because the commit 54f1944e("mptcp: factor out
mptcp_connect()") and 7439d687("mptcp: avoid a few atomic ops in the
rx path") are not merged]
Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>