Re: [PATCH v5] selinux: sidtab: reverse lookup hash table

[Jeffrey Vander Stoep <jeffv@google.com>]

> > > @@ -305,29 +284,36 @@ static int sidtab_reverse_lookup(struct sidtab *s, struct context *context,
> > >               rc = -ENOMEM;
> > >               dst_convert = sidtab_do_lookup(convert->target, count, 1);
> > >               if (!dst_convert) {
> > > -                     context_destroy(dst);
> > > +                     context_destroy(&dst->context);
> > >                       goto out_unlock;
> > >               }
> > >
> > > -             rc = convert->func(context, dst_convert, convert->args);
> > > +             rc = convert->func(context, &dst_convert->context,
> > > +                             convert->args);
> > >               if (rc) {
> > > -                     context_destroy(dst);
> > > +                     context_destroy(&dst->context);
> > >                       goto out_unlock;
> > >               }
> > > +             dst_convert->sid = index_to_sid(count);
> > > +             convert->target->count = count + 1;
> > >
> > >               /* at this point we know the insert won't fail */
> > > -             convert->target->count = count + 1;
> > > +             spin_lock_irqsave_nested(&convert->target->lock, flags,
> > > +                             SINGLE_DEPTH_NESTING);
> > > +             hash_add_rcu(convert->target->context_to_sid,
> > > +                             &dst_convert->list, dst_convert->context.hash);
> > > +             spin_unlock_irqrestore(&convert->target->lock, flags);
> >
> > Still having a hard time understanding why we need to lock the target.
> > The target here is always the newsidtab allocated by
> > security_load_policy(), not yet exposed to any other threads in the system?
>
> I believe this is to avoid a race with the hash_add() in
> sidtab_convert_hashtable(), which locks only the target table.
> However, I don't like the fact that we need to mess with inconsistent
> lock nesting here... I think it would be better to just lock the
> master's spinlock in sidtab_convert_hashtable() - it will then block
> more when entries would be added to sidtab, but that shouldn't be a
> big concern in practice.
>

I'll try that. Thanks.