[PATCH 5.15.y] mptcp: fix subflow bitfield misuse

[Sasha Levin <sashal@kernel.org>]

From: Paolo Abeni <pabeni@redhat.com>

[ Upstream commit 7538fa33bb2f66b8b809ff39d58308be48e197a0 ]

The subflow status bitfield is protected by the subflow socket lock,
with one notable exception: the `close_event_done` bit is actually under
the msk socket lock protection.

As reported by Clashiko [1], flipping the latter bit may corrupt other
entries in the same bitfield.

Move the `close_event_done` outside the bitfield, in a 32bit hole.

Link: https://lore.kernel.org/178959153492.22033.1944011998010756543@kernel.org
Fixes: d82809b6c5f2 ("mptcp: avoid duplicated SUB_CLOSED events")
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/20261013-net-mptcp-misc-fixes-7-3-rc8-v1-2-932c9b182fc7@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
[ sashal: adjusted __unused from 10 to 11 instead of 8 to 9 to match the existing mptcp_subflow_context layout ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/mptcp/protocol.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index 913d9b1474b05..4292836203d19 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -446,11 +446,13 @@ struct mptcp_subflow_context {
 		disposable : 1,	    /* ctx can be free at ulp release time */
 		stale : 1,	    /* unable to snd/rcv data, do not use for xmit */
 		valid_csum_seen : 1,        /* at least one csum validated */
-		close_event_done : 1,       /* has done the post-closed part */
 		resetting : 1,	    /* subflow is resetting */
-		__unused : 10;
+		__unused : 11;
 	enum mptcp_data_avail data_avail;
 	bool	pm_listener;	    /* a listener managed by the kernel PM? */
+	bool	close_event_done;   /* has done the post-closed part,
+				     * protected by msk socket lock
+				     */
 	u32	remote_nonce;
 	u64	thmac;
 	u32	local_nonce;
-- 
2.53.0