Re: [PATCH 14/15] kernel: convert futex_pi_state.refcount from atomic_t to refcount_t

Peter Zijlstra
2017-07-07T09:26:03Z

On Fri, Jul 07, 2017 at 12:04:28PM +0300, Elena Reshetova 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: Elena Reshetova <elena.reshetova@intel.com>
> Signed-off-by: Hans Liljestrand <ishkamiel@gmail.com>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> Signed-off-by: David Windsor <dwindsor@gmail.com>

I'll let tglx comment on the SoB chain, I know he likes those :-) You
did Cc him right, seeing how he's the maintainer of this stuff..

*sigh* you didn't :-( After so many patches send you _really_ should
know to Cc the right people.

> ---
> kernel/futex.c | 13 +++++++------
> 1 file changed, 7 insertions(+), 6 deletions(-)

> @@ -814,7 +815,7 @@ static struct futex_pi_state *alloc_pi_state(void)
>
> static void get_pi_state(struct futex_pi_state *pi_state)
> {
> - WARN_ON_ONCE(!atomic_inc_not_zero(&pi_state->refcount));
> + WARN_ON_ONCE(!refcount_inc_not_zero(&pi_state->refcount));
> }

I think we have refcount_inc() for just that case, no?