Re: [PATCH 2.6.32 19/38] [PATCH 19/38] pagemap: hide physical addresses from non-privileged users

[Ben Hutchings]

On Mon, 2015-11-30 at 12:30 +0100, Willy Tarreau wrote:
> On Mon, Nov 30, 2015 at 08:01:36AM +0100, Willy Tarreau wrote:
> > On Mon, Nov 30, 2015 at 01:54:22AM +0000, Ben Hutchings wrote:
> > > On Sun, 2015-11-29 at 22:47 +0100, Willy Tarreau wrote:
> > > This is wrong; see
> > > <https://marc.info/?l=linux-api&m=143144321020852&w=2>.
> > 
> > Damned, and I now remember this discussion. The worst thing is that
> > I purposely booted a machine to test the fix and was happy with it,
> > I forgot this point :-(
> > 
> > > For 2.6.32 perhaps you could retain the capability check at open time
> > > but store the result in private state for use at read time.
> > 
> > I'll see if it is possible to opencode security_capable() with 2.6.32's
> > infrastructure, and how far this brings us. Or maybe we should even drop
> > this one completely and leave pagemap readable only for superuser on
> > 2.6.32, it doesn't seem to be that big of a deal either.
> 
> It was easy enough to open-code security_capable() in the end. I've
> tested this version which works fine for me here. If that's OK for you
> I'll emit an -rc2 with the last two patches.
[...]
> +	/* do not disclose physical addresses: attack vector */
> +	pm.show_pfn = !cap_capable(current, file->f_cred, CAP_SYS_ADMIN, SECURITY_CAP_AUDIT);
[...]

But this bypasses SELinux's additional restrictions on capabilities.
I think it would be better to cherry-pick this first:

commit 6037b715d6fab139742c3df8851db4c823081561
Author: Chris Wright <chrisw@xxxxxxxxxxxx>
Date:ÂÂÂWed Feb 9 22:11:51 2011 -0800

ÂÂÂÂsecurity: add cred argument to security_capable()

and then you can pass file->f_cred to security_capable().

Ben.ÂÂÂÂ

-- 
Ben Hutchings
Who are all these weirdos? - David Bowie, reading IRC for the first time

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