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From: Richard Guy Briggs <rgb@redhat.com>
To: Paul Moore <paul@paul-moore.com>
Cc: Neil Horman <nhorman@tuxdriver.com>,
	containers@lists.linux-foundation.org, linux-api@vger.kernel.org,
	Linux-Audit Mailing List <linux-audit@redhat.com>,
	linux-fsdevel@vger.kernel.org,
	LKML <linux-kernel@vger.kernel.org>,
	netdev@vger.kernel.org, netfilter-devel@vger.kernel.org,
	sgrubb@redhat.com, omosnace@redhat.com, dhowells@redhat.com,
	simo@redhat.com, Eric Paris <eparis@parisplace.org>,
	Serge Hallyn <serge@hallyn.com>,
	ebiederm@xmission.com, Dan Walsh <dwalsh@redhat.com>,
	mpatel@redhat.com
Subject: Re: [PATCH ghak90 V7 06/21] audit: contid limit of 32k imposed to avoid DoS
Date: Thu, 24 Oct 2019 17:23:35 -0400
Message-ID: <20191024212335.y4ou7g4tsxnotvnk@madcap2.tricolour.ca> (raw)
In-Reply-To: <CAHC9VhRbSUCB0OZorC4+y+5uJDR5uMXdRn2LOTYGu2gcFJSrcA@mail.gmail.com>

On 2019-10-10 20:38, Paul Moore wrote:
> On Fri, Sep 27, 2019 at 8:52 AM Neil Horman <nhorman@tuxdriver.com> wrote:
> > On Wed, Sep 18, 2019 at 09:22:23PM -0400, Richard Guy Briggs wrote:
> > > Set an arbitrary limit on the number of audit container identifiers to
> > > limit abuse.
> > >
> > > Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
> > > ---
> > >  kernel/audit.c | 8 ++++++++
> > >  kernel/audit.h | 4 ++++
> > >  2 files changed, 12 insertions(+)
> > >
> > > diff --git a/kernel/audit.c b/kernel/audit.c
> > > index 53d13d638c63..329916534dd2 100644
> > > --- a/kernel/audit.c
> > > +++ b/kernel/audit.c
> 
> ...
> 
> > > @@ -2465,6 +2472,7 @@ int audit_set_contid(struct task_struct *task, u64 contid)
> > >                               newcont->owner = current;
> > >                               refcount_set(&newcont->refcount, 1);
> > >                               list_add_rcu(&newcont->list, &audit_contid_hash[h]);
> > > +                             audit_contid_count++;
> > >                       } else {
> > >                               rc = -ENOMEM;
> > >                               goto conterror;
> > > diff --git a/kernel/audit.h b/kernel/audit.h
> > > index 162de8366b32..543f1334ba47 100644
> > > --- a/kernel/audit.h
> > > +++ b/kernel/audit.h
> > > @@ -219,6 +219,10 @@ static inline int audit_hash_contid(u64 contid)
> > >       return (contid & (AUDIT_CONTID_BUCKETS-1));
> > >  }
> > >
> > > +extern int audit_contid_count;
> > > +
> > > +#define AUDIT_CONTID_COUNT   1 << 16
> > > +
> >
> > Just to ask the question, since it wasn't clear in the changelog, what
> > abuse are you avoiding here?  Ostensibly you should be able to create as
> > many container ids as you have space for, and the simple creation of
> > container ids doesn't seem like the resource strain I would be concerned
> > about here, given that an orchestrator can still create as many
> > containers as the system will otherwise allow, which will consume
> > significantly more ram/disk/etc.
> 
> I've got a similar question.  Up to this point in the patchset, there
> is a potential issue of hash bucket chain lengths and traversing them
> with a spinlock held, but it seems like we shouldn't be putting an
> arbitrary limit on audit container IDs unless we have a good reason
> for it.  If for some reason we do want to enforce a limit, it should
> probably be a tunable value like a sysctl, or similar.

Can you separate and clarify the concerns here?

I plan to move this patch to the end of the patchset and make it
optional, possibly adding a tuning mechanism.  Like the migration from
/proc to netlink for loginuid/sessionid/contid/capcontid, this was Eric
Biederman's concern and suggested mitigation.

As for the first issue of the bucket chain length traversal while
holding the list spin-lock, would you prefer to use the rcu lock to
traverse the list and then only hold the spin-lock when modifying the
list, and possibly even make the spin-lock more fine-grained per list?

> paul moore

- RGB

--
Richard Guy Briggs <rgb@redhat.com>
Sr. S/W Engineer, Kernel Security, Base Operating Systems
Remote, Ottawa, Red Hat Canada
IRC: rgb, SunRaycer
Voice: +1.647.777.2635, Internal: (81) 32635


  reply index

Thread overview: 69+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-19  1:22 [PATCH ghak90 V7 00/21] audit: implement container identifier Richard Guy Briggs
2019-09-19  1:22 ` [PATCH ghak90 V7 01/21] audit: collect audit task parameters Richard Guy Briggs
2019-09-19  1:22 ` [PATCH ghak90 V7 02/21] audit: add container id Richard Guy Briggs
2019-09-19  1:22 ` [PATCH ghak90 V7 03/21] audit: read container ID of a process Richard Guy Briggs
2019-09-19  1:22 ` [PATCH ghak90 V7 04/21] audit: convert to contid list to check for orch/engine ownership Richard Guy Briggs
2019-09-26 14:46   ` Neil Horman
2019-10-25 20:00     ` Richard Guy Briggs
2019-10-28 12:20       ` Neil Horman
2019-10-11  0:38   ` Paul Moore
2019-10-25 21:00     ` Richard Guy Briggs
2019-11-08 18:26       ` Paul Moore
2019-09-19  1:22 ` [PATCH ghak90 V7 05/21] audit: log drop of contid on exit of last task Richard Guy Briggs
2019-10-11  0:38   ` Paul Moore
2019-10-25 19:43     ` Richard Guy Briggs
2019-09-19  1:22 ` [PATCH ghak90 V7 06/21] audit: contid limit of 32k imposed to avoid DoS Richard Guy Briggs
2019-09-27 12:51   ` Neil Horman
2019-10-11  0:38     ` Paul Moore
2019-10-24 21:23       ` Richard Guy Briggs [this message]
2019-11-08 17:49         ` Paul Moore
2019-10-25 20:15     ` Richard Guy Briggs
2019-09-19  1:22 ` [PATCH ghak90 V7 07/21] audit: log container info of syscalls Richard Guy Briggs
2019-09-19  1:22 ` [PATCH ghak90 V7 08/21] audit: add contid support for signalling the audit daemon Richard Guy Briggs
2019-10-11  0:39   ` Paul Moore
2019-10-25 19:20     ` Richard Guy Briggs
2019-11-08 17:41       ` Paul Moore
2019-09-19  1:22 ` [PATCH ghak90 V7 09/21] audit: add support for non-syscall auxiliary records Richard Guy Briggs
2019-09-19  1:22 ` [PATCH ghak90 V7 10/21] audit: add containerid support for user records Richard Guy Briggs
2019-09-19  1:22 ` [PATCH ghak90 V7 11/21] audit: add containerid filtering Richard Guy Briggs
2019-09-19  1:22 ` [PATCH ghak90 V7 12/21] audit: add support for containerid to network namespaces Richard Guy Briggs
2019-10-11  0:39   ` Paul Moore
2019-09-19  1:22 ` [PATCH ghak90 V7 13/21] audit: NETFILTER_PKT: record each container ID associated with a netNS Richard Guy Briggs
2019-10-11  0:39   ` Paul Moore
2019-09-19  1:22 ` [PATCH ghak90 V7 14/21] audit: contid check descendancy and nesting Richard Guy Briggs
2019-10-11  0:40   ` Paul Moore
2019-10-24 22:08     ` Richard Guy Briggs
2019-10-30 20:32       ` Paul Moore
2019-09-19  1:22 ` [PATCH ghak90 V7 15/21] sched: pull task_is_descendant into kernel/sched/core.c Richard Guy Briggs
2019-10-11  0:40   ` Paul Moore
2019-09-19  1:22 ` [PATCH ghak90 V7 16/21] audit: add support for contid set/get by netlink Richard Guy Briggs
2019-10-11  0:40   ` Paul Moore
2019-09-19  1:22 ` [PATCH ghak90 V7 17/21] audit: add support for loginuid/sessionid " Richard Guy Briggs
2019-10-11  0:40   ` Paul Moore
2019-09-19  1:22 ` [PATCH ghak90 V7 18/21] audit: track container nesting Richard Guy Briggs
2019-10-11  0:40   ` Paul Moore
2019-09-19  1:22 ` [PATCH ghak90 V7 19/21] audit: check cont depth Richard Guy Briggs
2019-09-19  1:22 ` [PATCH ghak90 V7 20/21] audit: add capcontid to set contid outside init_user_ns Richard Guy Briggs
2019-10-19  1:39   ` Richard Guy Briggs
2019-10-21 19:53     ` Paul Moore
2019-10-21 21:38       ` Richard Guy Briggs
2019-10-21 21:43         ` Paul Moore
2019-10-21 23:57           ` Richard Guy Briggs
2019-10-22  0:31             ` Paul Moore
2019-10-22 12:13               ` Neil Horman
2019-10-22 14:04                 ` Paul Moore
2019-10-22 20:06                 ` Richard Guy Briggs
2019-10-22 14:27               ` Richard Guy Briggs
2019-10-22 14:34                 ` Paul Moore
2019-10-24 21:00               ` Richard Guy Briggs
2019-10-30 20:27                 ` Paul Moore
2019-10-30 22:03                   ` Richard Guy Briggs
2019-10-31 13:59                     ` Paul Moore
2019-10-31 14:50                     ` Steve Grubb
2019-10-31 23:37                       ` Paul Moore
2019-11-01  1:02                       ` Duncan Roe
2019-11-01 15:09                       ` Richard Guy Briggs
2019-11-01 15:13                         ` Steve Grubb
2019-11-01 15:21                           ` Richard Guy Briggs
2019-11-01 16:22                         ` Paul Moore
2019-09-19  1:22 ` [PATCH ghak90 V7 21/21] audit: add proc interface for capcontid Richard Guy Briggs

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