netdev - Re: [PATCH] cls_cgroup: read classid atomically in classifier

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]

Message-ID: <6599ad830905261439s63152c63s8b79f203600a2e5c@mail.gmail.com>
Date:	Tue, 26 May 2009 14:39:27 -0700
From:	Paul Menage <menage@...gle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	lizf@...fujitsu.com, davem@...emloft.net, tgraf@...g.ch,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] cls_cgroup: read classid atomically in classifier

On Tue, May 26, 2009 at 2:04 PM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Tue, 26 May 2009 12:59:11 -0700
> Paul Menage <menage@...gle.com> wrote:
>
>> Avoid reading the unsynchronized value cs->classid multiple times,
>> since it could change concurrently from non-zero to zero; this would
>> result in the classifier returning a positive result with a bogus
>> (zero) classid.
>
> When this race occurs, what are the user-visible consequences?

My guess is very little - rather than returning -1 to indicate that
there's no classid associated with the flow, we're returning a
positive response that the classid is 0. I don't know the network
scheduling code well enough to predict what effect that would have,
but I'd guess it results in the subsequent classid->queue lookup
failing and the packet being shunted down some default queue (unless
the user happens to have set up a queue with id 0). But the race looks
to be against the intent of the code, which is to return -1 if the
classid is 0, or fill in the res struct if it's non-zero.

>
> People who need to decide to which kernels a patch should be applied
> like to know such things.
>

I don't think this is a -stable candidate.

Paul
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html