linux-kernel - Re: [PATCH] Make /proc/slabinfo 0400

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Fri, 04 Mar 2011 12:14:55 -0600
From:	Matt Mackall <mpm@...enic.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Pekka Enberg <penberg@...nel.org>,
	Theodore Tso <tytso@....edu>,
	Dan Rosenberg <drosenberg@...curity.com>,
	cl@...ux-foundation.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] Make /proc/slabinfo 0400

On Fri, 2011-03-04 at 09:48 -0800, Linus Torvalds wrote:
> On Fri, Mar 4, 2011 at 9:36 AM, Dave Hansen <dave@...ux.vnet.ibm.com> wrote:
> >
> > We need to either keep the bad guys away from the counts (this patch),
> > or de-correlate the counts moving around with the position of objects in
> > the slab.  Ted's suggestion is a good one, and the only other thing I
> > can think of is to make the values useless, perhaps by batching and
> > delaying the (exposed) counts by a random amount.
> 
> We might just decide to expose the 'active' count for regular users
> (and then, in case there are tools there that parse this as normal
> users, we could set the 'total' fields to be the same as the active
> one, possibly rounded up to the slab allocation or something.
> 
> I know, I know, from a memory usage standpoint, 'active' is secondary,
> but it still correlates fairly well, so it's still useful.  And for
> seeing memory leaks (as opposed to slab fragmentation etc issues),
> it's actually the interesting case.
> 
> And at the same time, it's actually much less involved with actual
> physical allocations than 'total' is, and thus much less of an attack
> vector. The fact that we got another socket allocation when we opened
> a new socket is not "useful" information for an attacker, not in the
> way it is to see a hint of _where_ the socket got allocated.
> 
> Of course, as you say, '/proc/meminfo' still does give you the trigger
> for "oh, now somebody actually allocated a new page". That's totally
> independent of slabinfo, though (and knowing the number of active
> slabs would neither help nor hurt somebody who uses meminfo - you
> might as well allocate new sockets in a loop, and use _only_ meminfo
> to see when that allocated a new page).

I think lying to the user is much worse than changing the permissions.
The cost of the resulting confusion is WAY higher.

-- 
Mathematics is the supreme nostalgia of our time.


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/