Re: [PATCH 2/6] treewide: remove using list iterator after loop body as a ptr

Kees Cook
2022-03-02T20:59:43Z

On Wed, Mar 02, 2022 at 12:18:45PM -0800, Linus Torvalds wrote:
> On Wed, Mar 2, 2022 at 12:07 PM Kees Cook <keescook@chromium.org> wrote:
> >
> > I've long wanted to change kfree() to explicitly set pointers to NULL on
> > free. https://github.com/KSPP/linux/issues/87
>
> We've had this discussion with the gcc people in the past, and gcc
> actually has some support for it, but it's sadly tied to the actual
> function name (ie gcc has some special-casing for "free()")
>
> See
>
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94527
>
> for some of that discussion.
>
> Oh, and I see some patch actually got merged since I looked there last
> so that you can mark "deallocator" functions, but I think it's only
> for the context matching, not for actually killing accesses to the
> pointer afterwards.

Ah! I missed that getting added in GCC 11. But yes, there it is:

https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-malloc-function-attribute

Hah, now we may need to split __malloc from __alloc_size. ;)

I'd still like the NULL assignment behavior, though, since some things
can easily avoid static analysis.

--
Kees Cook