On Wed, 2018-09-26 at 22:06 +0200, Johannes Berg wrote:

From: Johannes Berg <redacted>

Without further bloating the policy structs, we can overload
the `validation_data' pointer with a struct of s16 min, max
and use those to validate ranges in NLA_{U,S}{8,16,32,64}
attributes.

It may sound strange to validate NLA_U32 with a s16 max, but
in many cases NLA_U32 is used for enums etc. since there's no
size benefit in using a smaller attribute width anyway, due
to netlink attribute alignment; in cases like that it's still
useful, particularly when the attribute really transports an
enum value.

That said, I did find a few places where we could benefit from a larger
type here - e.g. having a NLA_U16 that must be non-zero cannot be
represented in the policy as is, since you can't set max to 65535.

However, I don't think we want to push the policy struct to 12 bytes on
32-bit platforms? It's currently 16 bytes on 64-bit due to the pointer
(and alignment), but only 8 bytes on 32-bit.

Keeping the few places that needed this validation is unlikely to be a
larger win than the policy size increase due to the larger type.

johannes