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: Tue, 17 Dec 2019 13:45:41 -0500 [thread overview]
Message-ID: <20191217184541.tagssqt4zujbanf6@madcap2.tricolour.ca> (raw)
In-Reply-To: <CAHC9VhTrKVQNvTPoX5xdx-TUX_ukpMv2tNFFqLa2Njs17GuQMg@mail.gmail.com>
On 2019-11-08 12:49, Paul Moore wrote:
> On Thu, Oct 24, 2019 at 5:23 PM Richard Guy Briggs <rgb@redhat.com> wrote:
> > 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?
>
> "Why are you doing this?" is about as simple as I can pose the question.
It was more of a concern for total system resources, primarily memory,
but this is self-limiting and an arbitrary concern.
The other limit of depth of nesting has different concerns that arise
depending on how reporting is done.
> > 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.
>
> Okay, let's just drop it. I *really* don't like this approach of
> tossing questionable stuff at the end of the patchset; I get why you
> are doing it, but I think we really need to focus on keeping this
> changeset small. If the number of ACIDs (heh) become unwieldy the
> right solution is to improve the algorithms/structures, if we can't do
> that for some reason, *then* we can fall back to a limiting knob in a
> latter release.
Ok, I've dropped it. There are mitigations in place for large numbers
of contids and it can be limited later without breaking anything.
> > 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?
>
> Until we have a better idea of how this is going to be used, I think
> it's okay for now. It's also internal to the kernel so we can change
> it at any time. My comments about the locking/structs was only to try
> and think of some reason why one might want to limit the number of
> ACIDs since neither you or Eric provided any reasoning that I could
> see.
I've switched to using an rcu read lock on the list traversal and
spin-lock on list update.
> 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
next prev parent reply other threads:[~2019-12-17 18:46 UTC|newest]
Thread overview: 72+ 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
2019-11-08 17:49 ` Paul Moore
2019-12-17 18:45 ` Richard Guy Briggs [this message]
2019-12-17 19:25 ` Steve Grubb
2019-12-17 19:56 ` Richard Guy Briggs
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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