On Wed, May 29, 2019 at 11:29:05AM -0400, Paul Moore wrote:

On Wed, May 29, 2019 at 10:57 AM Tycho Andersen [off-list ref] wrote:

quoted

On Mon, Apr 08, 2019 at 11:39:09PM -0400, Richard Guy Briggs wrote:

quoted

It is not permitted to unset the audit container identifier.
A child inherits its parent's audit container identifier.

...

quoted

 /**
+ * audit_set_contid - set current task's audit contid
+ * @contid: contid value
+ *
+ * Returns 0 on success, -EPERM on permission failure.
+ *
+ * Called (set) from fs/proc/base.c::proc_contid_write().
+ */
+int audit_set_contid(struct task_struct *task, u64 contid)
+{
+     u64 oldcontid;
+     int rc = 0;
+     struct audit_buffer *ab;
+     uid_t uid;
+     struct tty_struct *tty;
+     char comm[sizeof(current->comm)];
+
+     task_lock(task);
+     /* Can't set if audit disabled */
+     if (!task->audit) {
+             task_unlock(task);
+             return -ENOPROTOOPT;
+     }
+     oldcontid = audit_get_contid(task);
+     read_lock(&tasklist_lock);
+     /* Don't allow the audit containerid to be unset */
+     if (!audit_contid_valid(contid))
+             rc = -EINVAL;
+     /* if we don't have caps, reject */
+     else if (!capable(CAP_AUDIT_CONTROL))
+             rc = -EPERM;
+     /* if task has children or is not single-threaded, deny */
+     else if (!list_empty(&task->children))
+             rc = -EBUSY;
+     else if (!(thread_group_leader(task) && thread_group_empty(task)))
+             rc = -EALREADY;
+     read_unlock(&tasklist_lock);
+     if (!rc)
+             task->audit->contid = contid;
+     task_unlock(task);
+
+     if (!audit_enabled)
+             return rc;

...but it is allowed to change it (assuming
capable(CAP_AUDIT_CONTROL), of course)? Seems like this might be more
immediately useful since we still live in the world of majority
privileged containers if we didn't allow changing it, in addition to
un-setting it.

The idea is that only container orchestrators should be able to
set/modify the audit container ID, and since setting the audit
container ID can have a significant effect on the records captured
(and their routing to multiple daemons when we get there) modifying
the audit container ID is akin to modifying the audit configuration
which is why it is gated by CAP_AUDIT_CONTROL.  The current thinking
is that you would only change the audit container ID from one
set/inherited value to another if you were nesting containers, in
which case the nested container orchestrator would need to be granted
CAP_AUDIT_CONTROL (which everyone to date seems to agree is a workable
compromise).

But then don't you want some kind of ns_capable() instead (probably
not the obvious one, though...)? With capable(), you can't really nest
using the audit-id and user namespaces together.

Tycho