From d1fefedc1a0e31cc8001f7702a2c51d07343a499 Mon Sep 17 00:00:00 2001
From: Davide Caratti <dcaratti@redhat.com>
Date: Fri, 29 Mar 2024 13:08:52 +0100
Subject: [PATCH] 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>
---
net/mptcp/protocol.c | 3 ---
net/mptcp/subflow.c | 2 ++
tools/testing/selftests/net/mptcp/mptcp_connect.sh | 7 +++++++
3 files changed, 9 insertions(+), 3 deletions(-)
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 3bc21581486ae..c652c8ca765c2 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -3349,9 +3349,6 @@ static struct sock *mptcp_accept(struct sock *sk, int flags, int *err,
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 891c2f4fed080..f1d422396b28b 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -816,6 +816,8 @@ static struct sock *subflow_syn_recv_sock(const struct sock *sk,
return child;
fallback:
+ if (fallback)
+ SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_MPCAPABLEPASSIVEFALLBACK);
mptcp_subflow_drop_ctx(child);
return child;
}
diff --git a/tools/testing/selftests/net/mptcp/mptcp_connect.sh b/tools/testing/selftests/net/mptcp/mptcp_connect.sh
index 18c9b00ca058e..dacf4cf2246da 100755
--- a/tools/testing/selftests/net/mptcp/mptcp_connect.sh
+++ b/tools/testing/selftests/net/mptcp/mptcp_connect.sh
@@ -439,6 +439,7 @@ 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 ${listener_ns} \
@@ -504,6 +505,7 @@ do_transfer()
local stat_cookietx_now=$(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))
@@ -548,6 +550,11 @@ 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
--
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