linux-kernel - Re: [PATCH] comedi: integer overflow in do_insnlist

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Message-ID: <CAKU6vyZdC64piK-mn6kLMt1-RhhM8D-4KbAGxje087FJ9X=fNA@mail.gmail.com>
Date:	Wed, 23 Nov 2011 08:59:52 -0500
From:	Xi Wang <xi.wang@...il.com>
To:	Dan Carpenter <dan.carpenter@...cle.com>
Cc:	linux-kernel@...r.kernel.org, devel@...verdev.osuosl.org,
	Mori Hess <fmhess@...rs.sourceforge.net>, security@...nel.org,
	Lucas De Marchi <lucas.demarchi@...fusion.mobi>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Ian Abbott <abbotti@....co.uk>,
	Franky Lin <frankyl@...adcom.com>,
	Greg Dietsche <Gregory.Dietsche@....edu>,
	Mark Pearson <markpearson_de@...oo.de>
Subject: Re: [PATCH] comedi: integer overflow in do_insnlist_ioctl()

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.

- xi

On Wed, Nov 23, 2011 at 1:13 AM, Dan Carpenter <dan.carpenter@...cle.com> wrote:
> I sent a patch for this already.
>
> http://driverdev.linuxdriverproject.org/pipermail/devel/2011-November/022469.html
>
> regards,
> dan carpenter
>
>
>
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