ceph: convert ceph_mds_session.s_ref 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 <ishkamiel@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David Windsor <dwindsor@gmail.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

1 files changed, 3 insertions, 2 deletions

diff --git a/fs/ceph/mds_client.h b/fs/ceph/mds_client.h
index ac0475a2daa7..bbebcd55d79e 100644
--- a/fs/ceph/mds_client.h
+++ b/fs/ceph/mds_client.h
@@ -7,6 +7,7 @@
 #include <linux/mutex.h>
 #include <linux/rbtree.h>
 #include <linux/spinlock.h>
+#include <linux/refcount.h>
 
 #include <linux/ceph/types.h>
 #include <linux/ceph/messenger.h>
@@ -156,7 +157,7 @@ struct ceph_mds_session {
 	unsigned long     s_renew_requested; /* last time we sent a renew req */
 	u64               s_renew_seq;
 
-	atomic_t          s_ref;
+	refcount_t          s_ref;
 	struct list_head  s_waiting;  /* waiting requests */
 	struct list_head  s_unsafe;   /* unsafe requests */
 };
@@ -373,7 +374,7 @@ __ceph_lookup_mds_session(struct ceph_mds_client *, int mds);
 static inline struct ceph_mds_session *
 ceph_get_mds_session(struct ceph_mds_session *s)
 {
-	atomic_inc(&s->s_ref);
+	refcount_inc(&s->s_ref);
 	return s;
 }