Re: [PATCH ghak90 V5 09/10] audit: add support for containerid to network namespaces

On Wed, Mar 27, 2019 at 9:12 PM Richard Guy Briggs <rgb(a)redhat.com&gt; wrote: > > On 2019-03-27 23:42, Ondrej Mosnacek wrote: > > On Fri, Mar 15, 2019 at 7:35 PM Richard Guy Briggs <rgb(a)redhat.com&gt; wrote: > > > Audit events could happen in a network namespace outside of a task > > > context due to packets received from the net that trigger an auditing > > > rule prior to being associated with a running task. The network > > > namespace could be in use by multiple containers by association to the > > > tasks in that network namespace. We still want a way to attribute > > > these events to any potential containers. Keep a list per network > > > namespace to track these audit container identifiiers. > > > > > > Add/increment the audit container identifier on: > > > - initial setting of the audit container identifier via /proc > > > - clone/fork call that inherits an audit container identifier > > > - unshare call that inherits an audit container identifier > > > - setns call that inherits an audit container identifier > > > Delete/decrement the audit container identifier on: > > > - an inherited audit container identifier dropped when child set > > > - process exit > > > - unshare call that drops a net namespace > > > - setns call that drops a net namespace > > > > > > See: https://github.com/linux-audit/audit-kernel/issues/92 > > > See: https://github.com/linux-audit/audit-testsuite/issues/64 > > > See: https://github.com/linux-audit/audit-kernel/wiki/RFE-Audit-Container-ID > > > Signed-off-by: Richard Guy Briggs <rgb(a)redhat.com&gt; > > > --- > > > include/linux/audit.h | 19 ++++++++++++ > > > kernel/audit.c | 86 +++++++++++++++++++++++++++++++++++++++++++++++++-- > > > kernel/nsproxy.c | 4 +++ > > > 3 files changed, 106 insertions(+), 3 deletions(-) > > > > > > diff --git a/include/linux/audit.h b/include/linux/audit.h > > > index fa19fa408931..70255c2dfb9f 100644 > > > --- a/include/linux/audit.h > > > +++ b/include/linux/audit.h > > > @@ -27,6 +27,7 @@ > > > #include <linux/ptrace.h> > > > #include <linux/namei.h> /* LOOKUP_* */ > > > #include <uapi/linux/audit.h> > > > +#include <linux/refcount.h> > > > > > > #define AUDIT_INO_UNSET ((unsigned long)-1) > > > #define AUDIT_DEV_UNSET ((dev_t)-1) > > > @@ -99,6 +100,13 @@ struct audit_task_info { > > > > > > extern struct audit_task_info init_struct_audit; > > > > > > +struct audit_contid { > > > + struct list_head list; > > > + u64 id; > > > + refcount_t refcount; > > > > Hm, since we only ever touch the refcount under a spinlock, I wonder > > if we could just make it a regular unsigned int (we don't need the > > atomicity guarantees). OTOH, refcount_t comes with some extra overflow > > checking, so it's probably better to leave it as is... > > Since the update is done using rcu-safe methods, do we even need the > spin_lock? Neil? Paul? As discussed, the refcount field is protected against simultaneous writes by the spinlock that protects additions/removals from the list as a whole so I don't believe the refcount_t atomicity is critical in this regard. Where it gets tricky, and I can't say I'm 100% confident on my answer here, is if refcount was a regular int and we wanted to access it outside of a spinlock (to be clear, it doesn't look like this patch currently does this). With RCU, if refcount was a regular int (unsigned or otherwise), I believe it would be possible for different threads of execution to potentially see different values of refcount (assuming one thread was adding/removing from the list). Using a refcount_t would protect against this, alternatively, taking the spinlock should also protect against this.

As we all know, RCU can be tricky at times, so I may be off on the above; if I am, please provide an explanation so I (and likely others as well) can learn a little bit more. :) -- paul moore www.paul-moore.com