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Message-ID: <20131114132539.GO5443@mwanda>
Date: Thu, 14 Nov 2013 16:25:39 +0300
From: Dan Carpenter <dan.carpenter@...cle.com>
To: Nico Golde <oss-security+ml@...lde.de>, oss-security@...ts.openwall.com,
security@...nel.org, "Hans J. Koch" <hjk@...sjkoch.de>
Subject: Re: some unstracked linux kernel security fixes
On Thu, Nov 14, 2013 at 11:33:10AM +0100, Petr Matousek wrote:
> On Tue, Nov 12, 2013 at 11:10:32AM +0100, Petr Matousek wrote:
> > Hi,
> >
> > On Sun, Nov 03, 2013 at 05:32:52PM +0100, Nico Golde wrote:
> > > drivers/uio/uio.c: mapping of physical memory to user space without proper size check
> > > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=7314e613d5ff
> >
> > there is a size check in uio_mmap() (the only caller of uio_mmap_physical()):
> >
> > requested_pages = vma_pages(vma);
> > actual_pages = ((idev->info->mem[mi].addr & ~PAGE_MASK)
> > + idev->info->mem[mi].size + PAGE_SIZE -1) >> PAGE_SHIFT;
> > if (requested_pages > actual_pages)
> > return -EINVAL;
> >
> > why it wasn't sufficient?
>
> Apparently there was a CVE split [1] and this is now CVE-2013-6763.
>
> http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2013-6763
>
> I still think this is a non-issue based on the above mentioned size
> check. Can I please get second opinion from someone more knowledgeable
> on this?
>
>
Added Hans to the CC list since he's the maintainer. Petr is asking if
the size checks in uio_mmap() and uio_mmap_physical() are duplicative.
> Isn't the size check redundant because of
>
> requested_pages = vma_pages(vma);
> actual_pages = ((idev->info->mem[mi].addr & ~PAGE_MASK)
> + idev->info->mem[mi].size + PAGE_SIZE -1) >> PAGE_SHIFT;
> if (requested_pages > actual_pages)
> return -EINVAL;
That check is worrying requested_pages is rounded down to the nearest
page but actual_pages is rounded up. I don't understand why we are
adding "(mem[mi]addr % PAGE_SIZE)" to the pre rounded up actual_pages.
So, yeah, it seems like we do check the size twice now except the first
time we do it wrong.
regards,
dan carpenter
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