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mptcp: fix bogus receive window shrinkage with multiple subflows

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commit 6bec041147 upstream.

In case multiple subflows race to update the mptcp-level receive
window, the subflow losing the race should use the window value
provided by the "winning" subflow to update it's own tcp-level
rcv_wnd.

To such goal, the current code bogusly uses the mptcp-level rcv_wnd
value as observed before the update attempt. On unlucky circumstances
that may lead to TCP-level window shrinkage, and stall the other end.

Address the issue feeding to the rcv wnd update the correct value.

Fixes: f3589be0c4 ("mptcp: never shrink offered window")
Cc: stable@vger.kernel.org
Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/427
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Paolo Abeni 2023-09-16 12:52:45 +02:00 committed by Greg Kroah-Hartman
parent 9e52fd5949
commit 2bef7c8c39
1 changed files with 3 additions and 2 deletions
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5
net/mptcp/options.c
View file

@ -1269,12 +1269,13 @@ static void mptcp_set_rwin(struct tcp_sock *tp, struct tcphdr *th)
if (rcv_wnd == rcv_wnd_old)
break;
if (before64(rcv_wnd_new, rcv_wnd)) {
rcv_wnd_old = rcv_wnd;
if (before64(rcv_wnd_new, rcv_wnd_old)) {
MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_RCVWNDCONFLICTUPDATE);
goto raise_win;
}
MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_RCVWNDCONFLICT);
rcv_wnd_old = rcv_wnd;
}
return;
}