hv_netvsc: Add (more) validation for untrusted Hyper-V values

hv_netvsc: Add (more) validation for untrusted Hyper-V values

For additional robustness in the face of Hyper-V errors or malicious
behavior, validate all values that originate from packets that Hyper-V
has sent to the guest.  Ensure that invalid values cannot cause indexing
off the end of an array, or subvert an existing validation via integer
overflow.  Ensure that outgoing packets do not have any leftover guest
memory that has not been zeroed out.

Reported-by: Juan Vazquez <juvazq@microsoft.com>
Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
Link: https://lore.kernel.org/r/20210114202628.119541-1-parri.andrea@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>