From 5d6613ed2b7dca6c5ed6dee8f9fd1dff5966e85f Mon Sep 17 00:00:00 2001 From: Paolo Abeni Date: Sat, 16 Sep 2023 12:52:45 +0200 Subject: [PATCH] mptcp: fix bogus receive window shrinkage with multiple subflows commit 6bec041147a2a64a490d1f813e8a004443061b38 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: f3589be0c420 ("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 Reviewed-by: Mat Martineau Signed-off-by: Matthieu Baerts Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- net/mptcp/options.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/net/mptcp/options.c b/net/mptcp/options.c index 6b2ef3bb53a3d..0c786ceda5ee6 100644 --- a/net/mptcp/options.c +++ b/net/mptcp/options.c @@ -1248,12 +1248,13 @@ 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; } -- 2.39.5