On Wed, Jul 29, 2020 at 4:06 PM Richard Guy Briggs <rgb@xxxxxxxxxx> wrote:
> On 2020-07-05 11:09, Paul Moore wrote:
> > On Sat, Jun 27, 2020 at 9:22 AM Richard Guy Briggs <rgb@xxxxxxxxxx> wrote:
...
> > > @@ -212,6 +219,33 @@ void __init audit_task_init(void)
> > > 0, SLAB_PANIC, NULL);
> > > }
> > >
> > > +/* rcu_read_lock must be held by caller unless new */
> > > +static struct audit_contobj *_audit_contobj_hold(struct audit_contobj *cont)
> > > +{
> > > + if (cont)
> > > + refcount_inc(&cont->refcount);
> > > + return cont;
> > > +}
> > > +
> > > +static struct audit_contobj *_audit_contobj_get(struct task_struct *tsk)
> > > +{
> > > + if (!tsk->audit)
> > > + return NULL;
> > > + return _audit_contobj_hold(tsk->audit->cont);
> > > +}
> > > +
> > > +/* rcu_read_lock must be held by caller */
> > > +static void _audit_contobj_put(struct audit_contobj *cont)
> > > +{
> > > + if (!cont)
> > > + return;
> > > + if (refcount_dec_and_test(&cont->refcount)) {
> > > + put_task_struct(cont->owner);
> > > + list_del_rcu(&cont->list);
> >
> > You should check your locking; I'm used to seeing exclusive locks
> > (e.g. the spinlock) around list adds/removes, it just reads/traversals
> > that can be done with just the RCU lock held.
>
> Ok, I've redone the locking yet again. I knew this on one level but
> that didn't translate consistently to code...
>
> > > + kfree_rcu(cont, rcu);
> > > + }
> > > +}
> >
> > Another nitpick, but it might be nice to have similar arguments to the
> > _get() and _put() functions, e.g. struct audit_contobj, but that is
> > some serious bikeshedding (basically rename _hold() to _get() and
> > rename _hold to audit_task_contid_hold() or similar).
>
> I have some idea what you are trying to say, but I think you misspoke.
> Did you mean rename _hold to _get, rename _get to
> audit_task_contobj_hold()?
It reads okay to me, but I know what I'm intending here :) I agree it
could be a bit confusing. Let me try to put my suggestion into some
quick pseudo-code function prototypes to make things a bit more
concrete.
The _audit_contobj_hold() function would become:
struct audit_contobj *_audit_contobj_hold(struct task_struct *tsk);
The _audit_contobj_get() function would become:
struct audit_contobj *_audit_contobj_get(struct audit_contobj *cont);
The _audit_contobj_put() function would become:
void _audit_contobj_put(struct audit_contobj *cont);
Basically swap the _get() and _hold() function names so that the
arguments are the same for both the _get() and _set() functions. Does
this make more sense?
> > > /**
> > > * audit_alloc - allocate an audit info block for a task
> > > * @tsk: task
> > > @@ -232,6 +266,9 @@ int audit_alloc(struct task_struct *tsk)
> > > }
> > > info->loginuid = audit_get_loginuid(current);
> > > info->sessionid = audit_get_sessionid(current);
> > > + rcu_read_lock();
> > > + info->cont = _audit_contobj_get(current);
> > > + rcu_read_unlock();
> >
> > The RCU locks aren't strictly necessary here, are they? In fact I
> > suppose we could probably just replace the _get() call with a
> > refcount_set(1) just as we do in audit_set_contid(), yes?
>
> I don't understand what you are getting at here. It needs a *contobj,
> along with bumping up the refcount of the existing contobj.
Sorry, you can disregard. My mental definition for audit_alloc() is
permanently messed up; I usually double check myself before commenting
on related code, but I must have forgotten here.
--
paul moore
www.paul-moore.com
