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Old 01-31-2008, 01:06 PM
Ben Collins
 
Default /dev/mem restrictions kernel patch

On Wed, 2008-01-30 at 19:49 -0800, Kees Cook wrote:
> On Wed, Jan 30, 2008 at 06:39:23PM -0800, Jeff Schroeder wrote:
> > Arjan van de Ven just posted a kernel patch for /dev/mem security that
> > looks interesting. It doesn't appear to be applied to ubuntu-hardy.git
> > or ubuntu-hardy-kees.git so I'm mentioning it now.
>
> Oh! This looks good. Arjan had mentioned these protections to me a
> while back, so I'm glad to see it has finally hit lkml.
>
> Unless someone on the kernel-team beats me to it, I'll put this into my
> tree for testing when I get back from vacation next week.

We had a similar patch before back in dapper, but the patch had major
conflicts past that, so was removed. Very useful though. I'd love to
have it back in there.

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Old 01-31-2008, 01:16 PM
Tim Gardner
 
Default /dev/mem restrictions kernel patch

Jeff Schroeder wrote:
> Sorry for the crosspost, but I'm not sure how many of the kernel team
> are on the hardened list.
>
> Arjan van de Ven just posted a kernel patch for /dev/mem security that
> looks interesting. It doesn't appear to be applied to ubuntu-hardy.git
> or ubuntu-hardy-kees.git so I'm mentioning it now.
>
> Since ubuntu appears to be taking a more proactive security approach,
> are there any thoughts about merging this into the Hardy kernel? It is
> a small patch that looks like a big win.
>
> Shamelessly ripped description from http://lkml.org/lkml/2008/1/30/473 :
> --------------------------------------
> This patch introduces a restriction on /dev/mem: Only non-memory can be
> read or written unless the newly introduced config option is set.
>
> The X server needs access to /dev/mem for the PCI space, but it doesn't need
> access to memory; both the file permissions and SELinux permissions of /dev/mem
> just make X effectively super-super powerful. With the exception of the
> BIOS area, there's just no valid app that uses /dev/mem on actual memory.
> Other popular users of /dev/mem are rootkits and the like.
> (note: mmap access of memory via /dev/mem was already not allowed since
> a really long time)
>
> People who want to use /dev/mem for kernel debugging can enable the config
> option.
>
> The restrictions of this patch have been in the Fedora and RHEL kernels for
> at least 4 years without any problems.
> --------------------------------------
>

+1 from me, but it doesn't apply cleanly to current Hardy. I'm gonna let
Kees handle integration and testing.

rtg

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