Re: [PATCH] ELF: implement AT_RANDOM for future glibc use

[Kees Cook <kees.cook@canonical.com>]

On Fri, Oct 03, 2008 at 02:43:40AM +0200, Jakub Jelinek wrote:
> On Thu, Oct 02, 2008 at 05:16:16PM -0700, Kees Cook wrote:
> > @@ -196,6 +198,18 @@ create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec,
> >  			return -EFAULT;
> >  	}
> >  
> > +	rand_size = CONFIG_SECURITY_AUXV_RANDOM_SIZE * sizeof(unsigned long);
> 
> I believe you want sizeof (elf_addr_t) here instead.
> 
> > +	u_rand_bytes = NULL;
> > +	if (rand_size) {
> > +		unsigned char k_rand_bytes[CONFIG_SECURITY_AUXV_RANDOM_SIZE *
> > +					   sizeof(unsigned long)];
> 
> And here too, because having a 64-bit kernel supply twice as much random
> data to 32-bit programs as a 32-bit kernel would supply would be certainly
> unexpected.

Ah-ha!  I see the 32-vs-64 elf_addr_t magic in fs/compat_binfmt_elf.c now.
Excellent, I will send an updated patch.

Thanks!

-Kees

-- 
Kees Cook
Ubuntu Security Team