Re: [PATCH net] net: nsh: fix incorrect header length macros

[Aaron Conole]

Ilya Maximets <i.maximets@xxxxxxx> writes:

> NSH header length is a 6-bit field that encodes the total length of
> the header in 4-byte words.  So the maximum length is 0b111111 * 4,
> which is 252 and not 256.  The maximum context length is the same
> number minus the length of the base header (8), so 244.
>
> These macros are used to validate push_nsh() action in openvswitch.
> Miscalculation here doesn't cause any real issues.  In the worst case
> the oversized context is truncated while building the header, so we'll
> construct and send a broken packet, which is not a big problem, as any
> receiver should validate the fields.  No invalid memory accesses will
> happen during the header push.  But we should fix the macros to reject
> the incorrect actions in the first place.
>
> Using previously defined values and calculating the length instead
> of defining numbers directly, so it's easier to understand where they
> come from and harder to make a mistake.
>
> Fixes: 1f0b7744c505 ("net: add NSH header structures and helpers")
> Signed-off-by: Ilya Maximets <i.maximets@xxxxxxx>
> ---

Thanks Ilya!

Reviewed-by: Aaron Conole <aconole@xxxxxxxxxx>