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 aed65bfe8480c1a7e4bd5a3783595c68151f4807..bcc94d03da21c72fc3a2de2d8ebb2d5801ab2081 100644 (file)
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -77,6 +77,13 @@ bool __mptcp_try_fallback(struct mptcp_sock *msk, int fb_mib)
        if (__mptcp_check_fallback(msk))
                return true;
 
+       /* 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_infinite_fallback) {
                spin_unlock_bh(&msk->fallback_lock);