From d6085fe19b8ec53d8ea2d8a10390b7ab6978ac44 Mon Sep 17 00:00:00 2001 From: Paolo Abeni Date: Thu, 30 Apr 2020 15:01:53 +0200 Subject: [PATCH] mptcp: avoid a WARN on bad input. Syzcaller has found a way to trigger the WARN_ON_ONCE condition in check_fully_established(). The root cause is a legit fallback to TCP scenario, so replace the WARN with a plain message on a more strict condition. Fixes: f296234c98a8 ("mptcp: Add handling of incoming MP_JOIN requests") Signed-off-by: Paolo Abeni Signed-off-by: David S. Miller --- net/mptcp/options.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/net/mptcp/options.c b/net/mptcp/options.c index eadbd59586e4c..ecf41d52d2fc4 100644 --- a/net/mptcp/options.c +++ b/net/mptcp/options.c @@ -703,8 +703,6 @@ static bool check_fully_established(struct mptcp_sock *msk, struct sock *sk, goto fully_established; } - WARN_ON_ONCE(subflow->can_ack); - /* If the first established packet does not contain MP_CAPABLE + data * then fallback to TCP */ @@ -714,6 +712,8 @@ static bool check_fully_established(struct mptcp_sock *msk, struct sock *sk, return false; } + if (unlikely(!READ_ONCE(msk->pm.server_side))) + pr_warn_once("bogus mpc option on established client sk"); subflow->fully_established = 1; subflow->remote_key = mp_opt->sndr_key; subflow->can_ack = 1;