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

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 <redacted>
Signed-off-by: Kees Cook <redacted>
Signed-off-by: David Windsor <redacted>
---
 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);
        }