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

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Message-ID: <20151130070136.GB31694@1wt.eu>
Date:	Mon, 30 Nov 2015 08:01:36 +0100
From:	Willy Tarreau <w@....eu>
To:	Ben Hutchings <ben@...adent.org.uk>
Cc:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Mark Williamson <mwilliamson@...o-software.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 2.6.32 19/38] [PATCH 19/38] pagemap: hide physical addresses from non-privileged users

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.

> The ptrace check presumably should also be done at open time, as was
> implemented upstream in:
> 
> commit a06db751c321546e5563041956a57613259c6720
> Author: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
> Date:   Tue Sep 8 14:59:59 2015 -0700
> 
>     pagemap: check permissions and capabilities at open time
> 
> But that wasn't cc'd to stable and hasn't been applied to any stable
> branch (yet).

I really prefer to avoid fixing things that are not in more recent
branches (especially upgrade candidates for 2.6.32 like yours).

Thanks!
Willy

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