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Tue, 17 Dec 2019 18:45:57 +0000 (UTC) Received: from madcap2.tricolour.ca (ovpn-112-28.phx2.redhat.com [10.3.112.28]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 27F125C1C3; Tue, 17 Dec 2019 18:45:43 +0000 (UTC) Date: Tue, 17 Dec 2019 13:45:41 -0500 From: Richard Guy Briggs To: Paul Moore Cc: Neil Horman , containers@lists.linux-foundation.org, linux-api@vger.kernel.org, Linux-Audit Mailing List , linux-fsdevel@vger.kernel.org, LKML , netdev@vger.kernel.org, netfilter-devel@vger.kernel.org, sgrubb@redhat.com, omosnace@redhat.com, dhowells@redhat.com, simo@redhat.com, Eric Paris , Serge Hallyn , ebiederm@xmission.com, Dan Walsh , mpatel@redhat.com Subject: Re: [PATCH ghak90 V7 06/21] audit: contid limit of 32k imposed to avoid DoS Message-ID: <20191217184541.tagssqt4zujbanf6@madcap2.tricolour.ca> References: <230e91cd3e50a3d8015daac135c24c4c58cf0a21.1568834524.git.rgb@redhat.com> <20190927125142.GA25764@hmswarspite.think-freely.org> <20191024212335.y4ou7g4tsxnotvnk@madcap2.tricolour.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20180716 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Sender: netfilter-devel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netfilter-devel@vger.kernel.org On 2019-11-08 12:49, Paul Moore wrote: > On Thu, Oct 24, 2019 at 5:23 PM Richard Guy Briggs wrote: > > On 2019-10-10 20:38, Paul Moore wrote: > > > On Fri, Sep 27, 2019 at 8:52 AM Neil Horman 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 > > > > > --- > > > > > 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 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