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 4cf8b7e48a ("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: 4cf8b7e48a ("subflow: introduce and use mptcp_can_accept_new_subflow()")
Tested-by: Davide Caratti <dcaratti@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Link: https://lore.kernel.org/r/03b2cfa3ac80d8fc18272edc6442a9ddf0b1e34e.1606400227.git.pabeni@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
d3ab78858f