linux-kernel - Re: [PATCH] ELF: implement AT

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Message-ID: <20081003052539.GR10632@outflux.net>
Date:	Thu, 2 Oct 2008 22:25:39 -0700
From:	Kees Cook <kees.cook@...onical.com>
To:	Jakub Jelinek <jakub@...hat.com>
Cc:	Roland McGrath <roland@...hat.com>, linux-kernel@...r.kernel.org,
	Ulrich Drepper <drepper@...hat.com>, libc-alpha@...rceware.org
Subject: Re: [PATCH] ELF: implement AT_RANDOM for future glibc use

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
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