mptcp: don't account accept() of non-MPC client as fallback to TCP

commit 7a1b3490f47e88ec4cbde65f1a77a0f4bc972282 upstream.

Current MPTCP servers increment MPTcpExtMPCapableFallbackACK when they
accept non-MPC connections. As reported by Christoph, this is "surprising"
because the counter might become greater than MPTcpExtMPCapableSYNRX.

MPTcpExtMPCapableFallbackACK counter's name suggests it should only be
incremented when a connection was seen using MPTCP options, then a
fallback to TCP has been done. Let's do that by incrementing it when
the subflow context of an inbound MPC connection attempt is dropped.
Also, update mptcp_connect.sh kselftest, to ensure that the
above MIB does not increment in case a pure TCP client connects to a
MPTCP server.

Fixes: fc518953bc9c ("mptcp: add and use MIB counter infrastructure")
Cc: stable@vger.kernel.org
Reported-by: Christoph Paasch <cpaasch@apple.com>
Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/449
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Reviewed-by: Mat Martineau <martineau@kernel.org>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://lore.kernel.org/r/20240329-upstream-net-20240329-fallback-mib-v1-1-324a8981da48@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index adbe6350f980b74c2d0385e2fe6fbfe886d02033..6be7e75922918fb2dab25bf7a420f15a74e7fc3e 100644 (file)
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -2218,9 +2218,6 @@ static struct sock *mptcp_accept(struct sock *sk, int flags, int *err,
 
                __MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_MPCAPABLEPASSIVEACK);
                local_bh_enable();
-       } else {
-               MPTCP_INC_STATS(sock_net(sk),
-                               MPTCP_MIB_MPCAPABLEPASSIVEFALLBACK);
        }
 
 out:

diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index 607519246bf2832759a20eccbfc537bc537dc2b1..276fe9f44df7342ebb755e1ba3865f6d2b658b7d 100644 (file)
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -595,6 +595,9 @@ create_child:
                        if (fallback_is_fatal)
                                goto dispose_child;
 
+                       if (fallback)
+                               SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_MPCAPABLEPASSIVEFALLBACK);
+
                        subflow_drop_ctx(child);
                        goto out;
                }