mptcp: consistent map handling on failure

When the MPTCP receive path reach a non fatal fall-back condition, e.g.
when the MPC sockets must fall-back to TCP, the existing code is a little
self-inconsistent: it reports that new data is available - return true -
but sets the MPC flag to the opposite value.

As the consequence read operations in some exceptional scenario may block
unexpectedly.

Address the issue setting the correct MPC read status. Additionally avoid
some code duplication in the fatal fall-back scenario.

Fixes: 9c81be0dbc89 ("mptcp: add MP_FAIL response support")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index b34b96fb742f92fe6932768845ae5a52f34df310..03862103665d69f27bf995618a266928314fb247 100644 (file)
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -1252,17 +1252,12 @@ fallback:
                        subflow->send_mp_fail = 1;
 
                        if (!READ_ONCE(msk->allow_infinite_fallback)) {
-                               ssk->sk_err = EBADMSG;
-                               tcp_set_state(ssk, TCP_CLOSE);
                                subflow->reset_transient = 0;
                                subflow->reset_reason = MPTCP_RST_EMIDDLEBOX;
-                               tcp_send_active_reset(ssk, GFP_ATOMIC);
-                               while ((skb = skb_peek(&ssk->sk_receive_queue)))
-                                       sk_eat_skb(ssk, skb);
-                       } else {
-                               mptcp_subflow_fail(msk, ssk);
+                               goto reset;
                        }
-                       WRITE_ONCE(subflow->data_avail, MPTCP_SUBFLOW_NODATA);
+                       mptcp_subflow_fail(msk, ssk);
+                       WRITE_ONCE(subflow->data_avail, MPTCP_SUBFLOW_DATA_AVAIL);
                        return true;
                }
 
@@ -1270,10 +1265,14 @@ fallback:
                        /* fatal protocol error, close the socket.
                         * subflow_error_report() will introduce the appropriate barriers
                         */
-                       ssk->sk_err = EBADMSG;
-                       tcp_set_state(ssk, TCP_CLOSE);
                        subflow->reset_transient = 0;
                        subflow->reset_reason = MPTCP_RST_EMPTCP;
+
+reset:
+                       ssk->sk_err = EBADMSG;
+                       tcp_set_state(ssk, TCP_CLOSE);
+                       while ((skb = skb_peek(&ssk->sk_receive_queue)))
+                               sk_eat_skb(ssk, skb);
                        tcp_send_active_reset(ssk, GFP_ATOMIC);
                        WRITE_ONCE(subflow->data_avail, MPTCP_SUBFLOW_NODATA);
                        return false;