From d3ab78858f1451351221061a1c365495df196500 Mon Sep 17 00:00:00 2001 From: Paolo Abeni Date: Thu, 26 Nov 2020 15:17:53 +0100 Subject: [PATCH] mptcp: fix NULL ptr dereference on bad MPJ If an msk listener receives an MPJ carrying an invalid token, it will zero the request socket msk entry. That should later cause fallback and subflow reset - as per RFC - at subflow_syn_recv_sock() time due to failing hmac validation. Since commit 4cf8b7e48a09 ("subflow: introduce and use mptcp_can_accept_new_subflow()"), we unconditionally dereference - in mptcp_can_accept_new_subflow - the subflow request msk before performing hmac validation. In the above scenario we hit a NULL ptr dereference. Address the issue doing the hmac validation earlier. Fixes: 4cf8b7e48a09 ("subflow: introduce and use mptcp_can_accept_new_subflow()") Tested-by: Davide Caratti Signed-off-by: Paolo Abeni Reviewed-by: Matthieu Baerts Link: https://lore.kernel.org/r/03b2cfa3ac80d8fc18272edc6442a9ddf0b1e34e.1606400227.git.pabeni@redhat.com Signed-off-by: Jakub Kicinski --- net/mptcp/subflow.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c index ac4a1fe3550b..953906e40742 100644 --- a/net/mptcp/subflow.c +++ b/net/mptcp/subflow.c @@ -543,9 +543,8 @@ static struct sock *subflow_syn_recv_sock(const struct sock *sk, fallback = true; } else if (subflow_req->mp_join) { mptcp_get_options(skb, &mp_opt); - if (!mp_opt.mp_join || - !mptcp_can_accept_new_subflow(subflow_req->msk) || - !subflow_hmac_valid(req, &mp_opt)) { + if (!mp_opt.mp_join || !subflow_hmac_valid(req, &mp_opt) || + !mptcp_can_accept_new_subflow(subflow_req->msk)) { SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_JOINACKMAC); fallback = true; }