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mptcp: reset fallback status gracefully at disconnect() time

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mptcp_disconnect() clears the fallback bit unconditionally, without
touching the associated flags.

The bit clear is safe, as no fallback operation can race with that --
all subflow are already in TCP_CLOSE status thanks to the previous
FASTCLOSE -- but we need to consistently reset all the fallback related
status.

Also acquire the relevant lock, to avoid fouling static analyzers.

Fixes: b29fcfb54c ("mptcp: full disconnect implementation")
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/20250714-net-mptcp-fallback-races-v1-3-391aff963322@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Paolo Abeni 2025-07-14 18:41:46 +02:00 committed by Jakub Kicinski
parent def5b7b264
commit da9b2fc7b7
1 changed files with 9 additions and 0 deletions
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9
net/mptcp/protocol.c
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@ -3142,7 +3142,16 @@ static int mptcp_disconnect(struct sock *sk, int flags)
* subflow
*/
mptcp_destroy_common(msk, MPTCP_CF_FASTCLOSE);
/* The first subflow is already in TCP_CLOSE status, the following
* can't overlap with a fallback anymore
*/
spin_lock_bh(&msk->fallback_lock);
msk->allow_subflows = true;
msk->allow_infinite_fallback = true;
WRITE_ONCE(msk->flags, 0);
spin_unlock_bh(&msk->fallback_lock);
msk->cb_flags = 0;
msk->recovery = false;
WRITE_ONCE(msk->can_ack, false);