Re: [PATCH 04/23] net, ceph: convert ceph_snap_context.nref from atomic_t to refcount_t

[Ilya Dryomov]

On Fri, Mar 17, 2017 at 1:10 PM, Elena Reshetova
<elena.reshetova@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: Elena Reshetova <elena.reshetova@xxxxxxxxx>
> Signed-off-by: Hans Liljestrand <ishkamiel@xxxxxxxxx>
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> Signed-off-by: David Windsor <dwindsor@xxxxxxxxx>
> ---
>  include/linux/ceph/libceph.h | 3 ++-
>  net/ceph/snapshot.c          | 6 +++---
>  2 files changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/ceph/libceph.h b/include/linux/ceph/libceph.h
> index 1816c5e..26dc674 100644
> --- a/include/linux/ceph/libceph.h
> +++ b/include/linux/ceph/libceph.h
> @@ -14,6 +14,7 @@
>  #include <linux/wait.h>
>  #include <linux/writeback.h>
>  #include <linux/slab.h>
> +#include <linux/refcount.h>
>
>  #include <linux/ceph/types.h>
>  #include <linux/ceph/messenger.h>
> @@ -159,7 +160,7 @@ struct ceph_client {
>   * dirtied.
>   */
>  struct ceph_snap_context {
> -       atomic_t nref;
> +       refcount_t nref;
>         u64 seq;
>         u32 num_snaps;
>         u64 snaps[];
> diff --git a/net/ceph/snapshot.c b/net/ceph/snapshot.c
> index 705414e..e14a5d0 100644
> --- a/net/ceph/snapshot.c
> +++ b/net/ceph/snapshot.c
> @@ -49,7 +49,7 @@ struct ceph_snap_context *ceph_create_snap_context(u32 snap_count,
>         if (!snapc)
>                 return NULL;
>
> -       atomic_set(&snapc->nref, 1);
> +       refcount_set(&snapc->nref, 1);
>         snapc->num_snaps = snap_count;
>
>         return snapc;
> @@ -59,7 +59,7 @@ EXPORT_SYMBOL(ceph_create_snap_context);
>  struct ceph_snap_context *ceph_get_snap_context(struct ceph_snap_context *sc)
>  {
>         if (sc)
> -               atomic_inc(&sc->nref);
> +               refcount_inc(&sc->nref);
>         return sc;
>  }
>  EXPORT_SYMBOL(ceph_get_snap_context);
> @@ -68,7 +68,7 @@ void ceph_put_snap_context(struct ceph_snap_context *sc)
>  {
>         if (!sc)
>                 return;
> -       if (atomic_dec_and_test(&sc->nref)) {
> +       if (refcount_dec_and_test(&sc->nref)) {
>                 /*printk(" deleting snap_context %p\n", sc);*/
>                 kfree(sc);
>         }

Applied.

Thanks,

                Ilya