Re: [PATCH] selinux: convert struct sidtab count to refcount_t

[Paul Moore]

On Mon, Jul 22, 2019 at 9:18 AM Ondrej Mosnacek <omosnace@xxxxxxxxxx> wrote:
> On Mon, Jul 22, 2019 at 1:35 PM NitinGote <nitin.r.gote@xxxxxxxxx> wrote:
> > refcount_t type and corresponding API should be
> > used instead of atomic_t when the variable is used as
> > a reference counter. This allows to avoid accidental
> > refcounter overflows that might lead to use-after-free
> > situations.
> >
> > Signed-off-by: NitinGote <nitin.r.gote@xxxxxxxxx>
>
> Nack.
>
> The 'count' variable is not used as a reference counter here. It
> tracks the number of entries in sidtab, which is a very specific
> lookup table that can only grow (the count never decreases). I only
> made it atomic because the variable is read outside of the sidtab's
> spin lock and thus the reads and writes to it need to be guaranteed to
> be atomic. The counter is only updated under the spin lock, so
> insertions do not race with each other.

Agreed, this should be changed to use refcount_t.

-- 
paul moore
www.paul-moore.com