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Date: Mon, 2 Dec 2013 19:40:29 -0800
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: "Hans J. Koch" <hjk@...sjkoch.de>,
Nico Golde <oss-security+ml@...lde.de>,
oss-security@...ts.openwall.com, security@...nel.org,
Dan Carpenter <dan.carpenter@...cle.com>
Subject: Re: kernel: uio: CVE-2013-6763 [was: Re: some
unstracked linux kernel security fixes]
On Tue, Nov 26, 2013 at 01:18:39PM +0100, Petr Matousek wrote:
> Adding Greg as he's also UIO maintainer (at least according to
> MAINTAINERS).
>
> On Thu, Nov 14, 2013 at 05:52:12PM +0100, Petr Matousek wrote:
> > On Thu, Nov 14, 2013 at 04:25:39PM +0300, Dan Carpenter wrote:
> > > 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
> >
> > Is there any rounding down happening? I would expect both vma->vm_start
> > and vma->vm_end to be page aligned.
> >
> > > 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.
> >
> > Imagine addr and size are not page aligned and
> > ((addr & ~PAGE_MASK) + (size & ~PAGE_MASK)) > PAGE_SIZE.
> > We need to round up two pages instead of one in that case.
> >
> > > So, yeah, it seems like we do check the size twice now except the first
> > > time we do it wrong.
> >
> > With unaligned addr and/or size we can end up with mapping memory
> > not belonging to the UIO_MEM_PHYS registered region, but that is something
> > you expect when using this interface from the drivers and/or userspace,
> > because you want access to the whole region to properly handle the
> > device, no?
> >
> > IOW, with the current changes, isn't the functionality broken for
> > non page-aligned addr and/or size?
This should now be fixed in Linus's tree, right?
thanks,
greg k-h
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