linux-kernel - Re: [PATCH] prctl: fix validation of an address

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Date:	Sun, 30 Dec 2012 17:03:07 -0500
From:	Eric Paris <eparis@...hat.com>
To:	Andrey Vagin <avagin@...nvz.org>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	James Morris <jmorris@...ei.org>
Subject: Re: [PATCH] prctl: fix validation of an address

On Sat, 2012-12-29 at 15:00 +0400, Andrey Vagin wrote:
> The address should be bigger than dac_mmap_min_addr, because
> a process with CAP_RAWIO can map a vma bellow mmap_min_addr.

NAK

This doesn't make any sense.  dac_mmap_min_addr should ONLY be used in
security/min_addr.c and security/commoncap.c.  Period.  You should not
be allowed to circumvent LSM protections.  Maybe you are missing that
mmap_min_addr = max(dac_mmap_min_addr, CONFIG_LSM_MMAP_MIN_ADDR)  ?

But this patch is absolutely unacceptable.  Maybe you can help me
understand what problem you had and what you were hoping for?

-Eric
> 
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Cyrill Gorcunov <gorcunov@...nvz.org>
> Cc: Serge Hallyn <serge.hallyn@...onical.com>
> Cc: "Eric W. Biederman" <ebiederm@...ssion.com>
> Cc: Eric Paris <eparis@...hat.com>
> Cc: James Morris <jmorris@...ei.org>
> Signed-off-by: Andrey Vagin <avagin@...nvz.org>
> ---
>  kernel/sys.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/sys.c b/kernel/sys.c
> index 265b376..e0e1bbd 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -1868,7 +1868,7 @@ static int prctl_set_mm(int opt, unsigned long addr,
>  	if (opt == PR_SET_MM_EXE_FILE)
>  		return prctl_set_mm_exe_file(mm, (unsigned int)addr);
>  
> -	if (addr >= TASK_SIZE || addr < mmap_min_addr)
> +	if (addr >= TASK_SIZE || addr < dac_mmap_min_addr)
>  		return -EINVAL;
>  
>  	error = -EINVAL;


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