ACK: [SRU Z/Y/T: CVE-2017-1000365] fs/exec.c: account for argv/envp pointers

[Seth Forshee]

On Wed, Jul 12, 2017 at 03:30:39PM +0200, Stefan Bader wrote:
> From: Kees Cook <keescook at chromium.org>
> 
> When limiting the argv/envp strings during exec to 1/4 of the stack limit,
> the storage of the pointers to the strings was not included.  This means
> that an exec with huge numbers of tiny strings could eat 1/4 of the stack
> limit in strings and then additional space would be later used by the
> pointers to the strings.
> 
> For example, on 32-bit with a 8MB stack rlimit, an exec with 1677721
> single-byte strings would consume less than 2MB of stack, the max (8MB /
> 4) amount allowed, but the pointers to the strings would consume the
> remaining additional stack space (1677721 * 4 == 6710884).
> 
> The result (1677721 + 6710884 == 8388605) would exhaust stack space
> entirely.  Controlling this stack exhaustion could result in
> pathological behavior in setuid binaries (CVE-2017-1000365).
> 
> [akpm at linux-foundation.org: additional commenting from Kees]
> Fixes: b6a2fea39318 ("mm: variable length argument support")
> Link: http://lkml.kernel.org/r/20170622001720.GA32173@beast
> Signed-off-by: Kees Cook <keescook at chromium.org>
> Acked-by: Rik van Riel <riel at redhat.com>
> Acked-by: Michal Hocko <mhocko at suse.com>
> Cc: Alexander Viro <viro at zeniv.linux.org.uk>
> Cc: Qualys Security Advisory <qsa at qualys.com>
> Cc: <stable at vger.kernel.org>
> Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
> Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
> 
> CVE-2017-1000365
> 
> (cherry-picked from commit 98da7d08850fb8bdeb395d6368ed15753304aa0c)
> Signed-off-by: Stefan Bader <stefan.bader at canonical.com>

For Y/Z:

Acked-by: Seth Forshee <seth.forshee at canonical.com>

Artful already got this commit from upstream stable.