Re: [PATCH ghak90 V7 06/21] audit: contid limit of 32k imposed to avoid DoS

On Fri, Sep 27, 2019 at 8:52 AM Neil Horman [off-list ref] wrote:

On Wed, Sep 18, 2019 at 09:22:23PM -0400, Richard Guy Briggs wrote:

quoted

Set an arbitrary limit on the number of audit container identifiers to
limit abuse.

Signed-off-by: Richard Guy Briggs <redacted>
---
 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

...

quoted

@@ -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.