Messages in this thread | | | Date | Thu, 24 Oct 2019 17:23:35 -0400 | From | Richard Guy Briggs <> | Subject | Re: [PATCH ghak90 V7 06/21] audit: contid limit of 32k imposed to avoid DoS |
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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
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