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From: Bodo Eggert <7eggert@gmx.de>
To: Andrew Morton <akpm@linux-foundation.org>,
	Jonathan Corbet <corbet@lwn.net>,
	linux-kernel@vger.kernel.org, torvalds@linux-foundation.org
Subject: Re: [PATCH] Avoid buffer overflows in get_user_pages()
Date: Tue, 12 Feb 2008 09:34:16 +0100	[thread overview]
Message-ID: <E1JOqan-0000hX-1T@be1.7eggert.dyndns.org> (raw)
In-Reply-To: <9VY4a-1tI-21@gated-at.bofh.it>

Andrew Morton <akpm@linux-foundation.org> wrote:
> On Mon, 11 Feb 2008 16:17:33 -0700 Jonathan Corbet <corbet@lwn.net> wrote:

>> Avoid buffer overflows in get_user_pages()
>> 
>> So I spent a while pounding my head against my monitor trying to figure
>> out the vmsplice() vulnerability - how could a failure to check for
>> *read* access turn into a root exploit?  It turns out that it's a buffer
>> overflow problem which is made easy by the way get_user_pages() is
>> coded.
>> 
>> In particular, "len" is a signed int, and it is only checked at the
>> *end* of a do {} while() loop.  So, if it is passed in as zero, the loop
>> will execute once and decrement len to -1.  At that point, the loop will
>> proceed until the next invalid address is found; in the process, it will
>> likely overflow the pages array passed in to get_user_pages().

[...]

> Can we just convert
> 
> do {
> ...
> } while (len);
> 
> into
> 
> while (len) {

while (len > 0), if I understand this patch correctly.


       reply	other threads:[~2008-02-12  8:34 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <9VQ6w-5Xn-7@gated-at.bofh.it>
     [not found] ` <9VY4a-1tI-21@gated-at.bofh.it>
2008-02-12  8:34   ` Bodo Eggert [this message]
     [not found] <fa.5jOFf0zR7ZoK3hLDItf3Omow4lE@ifi.uio.no>
     [not found] ` <fa.NNs+hqAlLlf93+yNZ/YJzSyGQbs@ifi.uio.no>
2008-02-12  3:16   ` Robert Hancock
2008-02-12  5:56     ` Nick Piggin
2008-02-11 23:17 Jonathan Corbet
2008-02-11 23:45 ` Nick Piggin
2008-02-12  7:46 ` Andrew Morton
2008-02-12 10:35   ` Jiri Kosina
2008-02-14 16:45 ` Oliver Pinter
2008-02-14 21:09   ` Jonathan Corbet

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