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 <[email protected]>
Signed-off-by: Paolo Abeni <[email protected]>
---
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;
}
--
2.26.2
