From: Lars-Peter Clausen <lars@metafoo.de>
To: Ian Abbott <abbotti@mev.co.uk>
Cc: Dan Carpenter <dan.carpenter@oracle.com>,
Xi Wang <xi.wang@gmail.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"devel@driverdev.osuosl.org" <devel@driverdev.osuosl.org>,
Mori Hess <fmhess@users.sourceforge.net>,
"security@kernel.org" <security@kernel.org>,
Lucas De Marchi <lucas.demarchi@profusion.mobi>,
Greg Kroah-Hartman <gregkh@suse.de>,
Ian Abbott <ian.abbott@mev.co.uk>,
Franky Lin <frankyl@broadcom.com>,
Greg Dietsche <Gregory.Dietsche@cuw.edu>,
Mark Pearson <markpearson_de@yahoo.de>
Subject: Re: [PATCH] comedi: integer overflow in do_insnlist_ioctl()
Date: Wed, 23 Nov 2011 22:41:07 +0100 [thread overview]
Message-ID: <4ECD6873.7080106@metafoo.de> (raw)
In-Reply-To: <4ECD1A01.3060503@mev.co.uk>
On 11/23/2011 05:06 PM, Ian Abbott wrote:
> On 2011-11-23 14:50, Dan Carpenter wrote:
>> On Wed, Nov 23, 2011 at 08:59:52AM -0500, Xi Wang wrote:
>>> Thanks for the pointer. However you cannot do the overflow check using
>>>
>>> if (sizeof(struct comedi_insn) * insnlist.n_insns <
>>> insnlist.n_insns)
>>>
>>> Let's assume 32-bit system, sizeof(struct comedi_insn) = 32, and
>>> insnlist.n_insns = 0x7fffffff.
>>>
>>> Note that 32 * 0x7fffffff = 0xffffffe0 overflows but bypasses your
>>> check.
>>>
>>
>> Argh... You're right, my check is wrong. What I like about my patch
>> though is that it doesn't introduce an arbitrary limit. Could you
>> redo your check without the MAX_INSNS?
>
> Could use something like:
>
> if (insnlist.n_insns <= ULONG_MAX / sizeof(struct comedi_insn))
> insns =
> kmalloc(sizeof(struct comedi_insn) * insnlist.n_insns,
> GFP_KERNEL);
> if (!insns)
> ...
>
> (note that insns is initialized to NULL).
>
Just use kcalloc, it will do the right thing for you.
- Lars
next prev parent reply other threads:[~2011-11-23 21:41 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-11-23 0:49 [PATCH] comedi: integer overflow in do_insnlist_ioctl() Xi Wang
2011-11-23 6:13 ` Dan Carpenter
2011-11-23 13:59 ` Xi Wang
2011-11-23 14:50 ` Dan Carpenter
2011-11-23 16:06 ` Ian Abbott
2011-11-23 16:53 ` [PATCH v2] " Xi Wang
2011-11-23 21:41 ` Lars-Peter Clausen [this message]
2011-11-23 21:51 ` [PATCH] " Dan Carpenter
2011-11-24 19:07 ` Xi Wang
2011-11-25 7:25 ` Dan Carpenter
2011-11-25 21:46 ` [PATCH v3] " Xi Wang
2011-11-27 2:52 ` Greg KH
2011-11-27 11:25 ` Dan Carpenter
2011-11-27 21:24 ` Greg KH
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=4ECD6873.7080106@metafoo.de \
--to=lars@metafoo.de \
--cc=Gregory.Dietsche@cuw.edu \
--cc=abbotti@mev.co.uk \
--cc=dan.carpenter@oracle.com \
--cc=devel@driverdev.osuosl.org \
--cc=fmhess@users.sourceforge.net \
--cc=frankyl@broadcom.com \
--cc=gregkh@suse.de \
--cc=ian.abbott@mev.co.uk \
--cc=linux-kernel@vger.kernel.org \
--cc=lucas.demarchi@profusion.mobi \
--cc=markpearson_de@yahoo.de \
--cc=security@kernel.org \
--cc=xi.wang@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox