hv_netvsc: Copy packets sent by Hyper-V out of the receive buffer

hv_netvsc: Copy packets sent by Hyper-V out of the receive buffer

Pointers to receive-buffer packets sent by Hyper-V are used within the
guest VM.  Hyper-V can send packets with erroneous values or modify
packet fields after they are processed by the guest.  To defend against
these scenarios, copy (sections of) the incoming packet after validating
their length and offset fields in netvsc_filter_receive().  In this way,
the packet can no longer be modified by the host.

Reported-by: Juan Vazquez <juvazq@microsoft.com>
Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
Link: https://lore.kernel.org/r/20210126162907.21056-1-parri.andrea@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>