Re: [PATCH 1/2] netlink: Bounds-check nlmsg_len()

[Jakub Kicinski]

On Wed, 31 Aug 2022 23:27:08 -0700 Kees Cook wrote:
> This would catch corrupted values...
> 
> Is the concern the growth in image size? The check_sub_overflow() isn't
> large at all -- it's just adding a single overflow bit test. The WARNs
> are heavier, but they're all out-of-line.

It turns the most obvious function into a noodle bar :(

Looking at this function in particular is quite useful, because 
it clearly indicates that the nlmsg_len includes the header.

How about we throw in a

	WARN_ON_ONCE(nlh->nlmsg_len < NLMSG_HDRLEN ||
		     nlh->nlmsg_len > INT_MAX);

but leave the actual calculation human readable C?