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Thu, 24 Oct 2019 21:23:51 +0000 (UTC) Received: from madcap2.tricolour.ca (ovpn-112-19.phx2.redhat.com [10.3.112.19]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 13D9D600C6; Thu, 24 Oct 2019 21:23:37 +0000 (UTC) Date: Thu, 24 Oct 2019 17:23:35 -0400 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: <20191024212335.y4ou7g4tsxnotvnk@madcap2.tricolour.ca> References: <230e91cd3e50a3d8015daac135c24c4c58cf0a21.1568834524.git.rgb@redhat.com> <20190927125142.GA25764@hmswarspite.think-freely.org> MIME-Version: 1.0 In-Reply-To: User-Agent: NeoMutt/20180716 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-MC-Unique: PWtRXmUyOIOZMecadsE0tQ-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 t= o > > > 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 >=20 > ... >=20 > > > @@ -2465,6 +2472,7 @@ int audit_set_contid(struct task_struct *task, = u64 contid) > > > newcont->owner =3D current; > > > refcount_set(&newcont->refcount, 1); > > > list_add_rcu(&newcont->list, &audit_con= tid_hash[h]); > > > + audit_contid_count++; > > > } else { > > > rc =3D -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 a= s > > 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 concerne= d > > 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. >=20 > 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 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 From mboxrd@z Thu Jan 1 00:00:00 1970 From: Richard Guy Briggs 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> References: <230e91cd3e50a3d8015daac135c24c4c58cf0a21.1568834524.git.rgb@redhat.com> <20190927125142.GA25764@hmswarspite.think-freely.org> Mime-Version: 1.0 Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: Content-Disposition: inline Sender: netdev-owner@vger.kernel.org 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 List-Id: linux-api@vger.kernel.org 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 t= o > > > 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 >=20 > ... >=20 > > > @@ -2465,6 +2472,7 @@ int audit_set_contid(struct task_struct *task, = u64 contid) > > > newcont->owner =3D current; > > > refcount_set(&newcont->refcount, 1); > > > list_add_rcu(&newcont->list, &audit_con= tid_hash[h]); > > > + audit_contid_count++; > > > } else { > > > rc =3D -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 a= s > > 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 concerne= d > > 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. >=20 > 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