mptcp: do not fallback when OoO is present

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>

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index e30e9043a69437b206457c470d3f95001bf7503c..6f0e8f670d837aef21a8c0a143e861ddca5db797 100644 (file)
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -76,6 +76,13 @@ 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);