|From:||Matt Mackall <mpm-AT-selenic.com>|
|To:||Linus Torvalds <torvalds-AT-linux-foundation.org>|
|Subject:||Re: [Security] [PATCH] proc: avoid information leaks to non-privileged processes|
|Date:||Wed, 6 May 2009 19:50:16 -0500|
|Cc:||Ingo Molnar <mingo-AT-elte.hu>, "Eric W. Biederman" <ebiederm-AT-xmission.com>, Arjan van de Ven <arjan-AT-infradead.org>, Jake Edge <jake-AT-lwn.net>, security-AT-kernel.org, Linux Kernel Mailing List <linux-kernel-AT-vger.kernel.org>, James Morris <jmorris-AT-namei.org>, linux-security-module-AT-vger.kernel.org, Eric Paris <eparis-AT-redhat.com>, Alan Cox <alan-AT-lxorguk.ukuu.org.uk>, Roland McGrath <roland-AT-redhat.com>, mingo-AT-redhat.com, Andrew Morton <akpm-AT-linux-foundation.org>, Greg KH <greg-AT-kroah.com>, Dave Jones <davej-AT-redhat.com>|
On Wed, May 06, 2009 at 12:57:17PM -0500, Matt Mackall wrote: > On Wed, May 06, 2009 at 09:48:20AM -0700, Linus Torvalds wrote: > > > > Matt, are you willing to ack my suggested patch which adds history to the > > mix? Did somebody test that? I have this memory of there being an > > "exploit" program to show the non-randomness of the values, but I can't > > recall details, and would really want to get a second opinion from > > somebody who cares about PRNG's. > > I still don't like it. I bounced it off some folks on the adversarial > side of things and they didn't think it looked strong enough either. > Full MD5 collisions can be generated about as fast as they can be > checked, which makes _reduced strength_ MD4 not much better than an > LFSR in terms of attack potential. So I suggest we either: > > a) take my original patch > b) respin your patch using at least SHA1 rather than halfMD4 and > changing the name to get_random_u32 > > If you'd prefer (b), I'll do the legwork. I've done some basic benchmarks on the primitives here in userspace: halfMD4 get_random_int: about .326us per call or 12.2MB/s sha1 get_random_int: about .660us per call or 6.1MB/s dd /dev/urandom: 3.6MB/s So I think the SHA1 solution is quite competitive on the performance front with far fewer concerns about its strength. I'll spin a proper patch tomorrow. -- Mathematics is the supreme nostalgia of our time. -- To unsubscribe from this list: send the line "unsubscribe linux-security-module" in the body of a message to email@example.com More majordomo info at http://vger.kernel.org/majordomo-info.html
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