linux-kernel - Re: [kernel-hardening] [PATCH] exec: Account for argv/envp pointers

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Message-ID: <1498095554.13083.25.camel@redhat.com>
Date:   Wed, 21 Jun 2017 21:39:14 -0400
From:   Rik van Riel <riel@...hat.com>
To:     Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Qualys Security Advisory <qsa@...lys.com>,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com
Subject: Re: [kernel-hardening] [PATCH] exec: Account for argv/envp pointers

On Wed, 2017-06-21 at 17:17 -0700, Kees Cook wrote:
> 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).
> 
> Fixes: b6a2fea39318 ("mm: variable length argument support")
> Cc: stable@...r.kernel.org
> Signed-off-by: Kees Cook <keescook@...omium.org>

Acked-by: Rik van Riel <riel@...hat.com>