Re: [PATCH 4/6] string: Add __realloc_size hint to kmemdup()

[Kees Cook <keescook@chromium.org>]

On Wed, Nov 02, 2022 at 10:26:40AM +0100, Rasmus Villemoes wrote:
> On 01/11/2022 23.33, Kees Cook wrote:
> > Add __realloc_size() hint to kmemdup() so the compiler can reason about
> > the length of the returned buffer. (These must not use __alloc_size,
> > since those include __malloc which says the contents aren't defined[1]).
> > 
> > [1] https://lore.kernel.org/linux-hardening/d199c2af-06af-8a50-a6a1-00eefa0b67b4@prevas.dk/
> > 
> 
> >  extern char *kstrndup(const char *s, size_t len, gfp_t gfp);
> > -extern void *kmemdup(const void *src, size_t len, gfp_t gfp) __alloc_size(2);
> > +extern void *kmemdup(const void *src, size_t len, gfp_t gfp) __realloc_size(2);
> 
> What tree is this based on? I see that kmemdup() has grown that bogus
> __alloc_size in next-20221101, but in next-20221102 this commit seems to
> DTRT, namely
> 
> -extern void *kmemdup(const void *src, size_t len, gfp_t gfp);
> +extern void *kmemdup(const void *src, size_t len, gfp_t gfp)
> __realloc_size(2);
> 
> (i.e. there should never be an intermediate commit where kmemdup has
> __alloc_size()).

Right -- I fixed in in my -next tree to not use __alloc_size.

-- 
Kees Cook