From: Paolo Abeni <pab...@redhat.com> [ Upstream commit d3ab78858f1451351221061a1c365495df196500 ]
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 <dcara...@redhat.com> Signed-off-by: Paolo Abeni <pab...@redhat.com> Reviewed-by: Matthieu Baerts <matthieu.bae...@tessares.net> Link: https://lore.kernel.org/r/03b2cfa3ac80d8fc18272edc6442a9ddf0b1e34e.1606400227.git.pab...@redhat.com Signed-off-by: Jakub Kicinski <k...@kernel.org> Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org> --- net/mptcp/subflow.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) --- a/net/mptcp/subflow.c +++ b/net/mptcp/subflow.c @@ -542,9 +542,8 @@ create_msk: 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; }