mptcp: do not fallback when OoO is present

commit 1bba3f219c5e8c29e63afa3c1fc24f875ebec119 upstream.

In case of DSS corruption, the MPTCP protocol tries to avoid the subflow
reset if fallback is possible. Such corruptions happen in the receive
path; to ensure fallback is possible the stack additionally needs to
check for OoO data, otherwise the fallback will break the data stream.

Fixes: e32d262c89e2 ("mptcp: handle consistently DSS corruption")
Cc: stable@vger.kernel.org
Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/598
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/20251118-net-mptcp-misc-fixes-6-18-rc6-v1-4-806d3781c95f@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 6c1f96f6ae392e972cfb5cc6d2426817956746d3..0087a598a383d8518a04ac3e90a62239795a521b 100644 (file)
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -906,6 +906,13 @@ static bool __mptcp_finish_join(struct mptcp_sock *msk, struct sock *ssk)
        if (sk->sk_state != TCP_ESTABLISHED)
                return false;
 
+       /* The caller possibly is not holding the msk socket lock, but
+        * in the fallback case only the current subflow is touching
+        * the OoO queue.
+        */
+       if (!RB_EMPTY_ROOT(&msk->out_of_order_queue))
+               return false;
+
        spin_lock_bh(&msk->fallback_lock);
        if (!msk->allow_subflows) {
                spin_unlock_bh(&msk->fallback_lock);