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 5db1c0142abb45dd5a6b0d03f0ace8819c057688..cde62dafda492761ca1628f99f4411e22cc9af9f 100644 (file)
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -3018,9 +3018,6 @@ static struct sock *mptcp_accept(struct sock *sk, int flags, int *err,
                sock_hold(new_mptcp_sock);
                newsk = new_mptcp_sock;
                MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_MPCAPABLEPASSIVEACK);
-       } else {
-               MPTCP_INC_STATS(sock_net(sk),
-                               MPTCP_MIB_MPCAPABLEPASSIVEFALLBACK);
        }
 
 out:

diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index 80230787554edcf4ef0ff320bc798d00e829338b..ff7239fe3d2cd69fb51a1dd4e88f006366220644 100644 (file)
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -725,6 +725,9 @@ create_child:
                                goto dispose_child;
                        }
 
+                       if (fallback)
+                               SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_MPCAPABLEPASSIVEFALLBACK);
+
                        subflow_drop_ctx(child);
                        goto out;
                }

diff --git a/tools/testing/selftests/net/mptcp/mptcp_connect.sh b/tools/testing/selftests/net/mptcp/mptcp_connect.sh
index 8efff3f9c52a9e94e16373ffa12ebfe5242d4d9a..5a1277d1728656cf09663e0c611666694f935fc0 100755 (executable)
--- a/tools/testing/selftests/net/mptcp/mptcp_connect.sh
+++ b/tools/testing/selftests/net/mptcp/mptcp_connect.sh
@@ -451,6 +451,7 @@ do_transfer()
        local stat_cookierx_last=$(get_mib_counter "${listener_ns}" "TcpExtSyncookiesRecv")
        local stat_csum_err_s=$(get_mib_counter "${listener_ns}" "MPTcpExtDataCsumErr")
        local stat_csum_err_c=$(get_mib_counter "${connector_ns}" "MPTcpExtDataCsumErr")
+       local stat_tcpfb_last_l=$(get_mib_counter "${listener_ns}" "MPTcpExtMPCapableFallbackACK")
 
        timeout ${timeout_test} \
                ip netns exec ${listener_ns} \
@@ -516,6 +517,7 @@ do_transfer()
        local stat_cookietx_now=$(get_mib_counter "${listener_ns}" "TcpExtSyncookiesSent")
        local stat_cookierx_now=$(get_mib_counter "${listener_ns}" "TcpExtSyncookiesRecv")
        local stat_ooo_now=$(get_mib_counter "${listener_ns}" "TcpExtTCPOFOQueue")
+       local stat_tcpfb_now_l=$(get_mib_counter "${listener_ns}" "MPTcpExtMPCapableFallbackACK")
 
        expect_synrx=$((stat_synrx_last_l))
        expect_ackrx=$((stat_ackrx_last_l))
@@ -560,6 +562,11 @@ do_transfer()
                fi
        fi
 
+       if [ ${stat_ooo_now} -eq 0 ] && [ ${stat_tcpfb_last_l} -ne ${stat_tcpfb_now_l} ]; then
+               printf "[ FAIL ]\nunexpected fallback to TCP"
+               rets=1
+       fi
+
        if [ $retc -eq 0 ] && [ $rets -eq 0 ]; then
                printf "[ OK ]"
        fi