Re: [PATCH 10/10] audit: Replace chunk attached to mark instead of replacing mark

[Jan Kara <jack@suse.cz>]

On Fri 27-07-18 00:47:42, Paul Moore wrote:
> On Tue, Jul 10, 2018 at 6:02 AM Jan Kara <jack@suse.cz> wrote:
> > diff --git a/kernel/audit_tree.c b/kernel/audit_tree.c
> > index aec9b27a20ff..40f61de77dd0 100644
> > --- a/kernel/audit_tree.c
> > +++ b/kernel/audit_tree.c
> > @@ -272,6 +273,20 @@ static struct audit_chunk *find_chunk(struct node *p)
> >         return container_of(p, struct audit_chunk, owners[0]);
> >  }
> >
> > +static void replace_mark_chunk(struct fsnotify_mark *entry,
> > +                              struct audit_chunk *chunk)
> > +{
> > +       struct audit_chunk *old;
> > +
> > +       assert_spin_locked(&hash_lock);
> > +       old = AUDIT_M(entry)->chunk;
> > +       AUDIT_M(entry)->chunk = chunk;
> > +       if (chunk)
> > +               chunk->mark = entry;
> > +       if (old)
> > +               old->mark = NULL;
> 
> Is it necessary that we check to see if chunk and old are non-NULL?
> It seems like we would always want to set chunk->mark to entry and set
> old->mark to NULL, yes?

Both checks are needed - 'old' can be NULL if we use replace_mark_chunk()
to attach first chunk to mark. 'chunk' can be NULL if we use
replace_mark_chunk() to detach mark from current chunk when destroying it.

> > @@ -321,29 +341,31 @@ static void untag_chunk(struct node *p)
> >
> >         mutex_lock(&entry->group->mark_mutex);
> >         /*
> > -        * mark_mutex protects mark from getting detached and thus also from
> > -        * mark->connector->obj getting NULL.
> > +        * mark_mutex protects mark stabilizes chunk attached to the mark so we
> > +        * can check whether it didn't change while we've dropped hash_lock.
> 
> I think your new text could use some revision, the "protects mark
> stabilizes chunk" is odd.

Yup, I'll fix that.

> >          */
> > -       if (chunk->dead || !(entry->flags & FSNOTIFY_MARK_FLAG_ATTACHED)) {
> > +       if (!(entry->flags & FSNOTIFY_MARK_FLAG_ATTACHED) ||
> > +           AUDIT_M(entry)->chunk != chunk) {
> >                 mutex_unlock(&entry->group->mark_mutex);
> >                 if (new)
> > -                       fsnotify_put_mark(new->mark);
> > +                       kfree(new);
> 
> Since we are just calling kfree() now we can do away with the "if (new)"
> check.

Right, I'll do that.

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR