libceph: convert ceph_pagelist.refcnt 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>

fs/ceph/mds_client.c

@@ -1991,7 +1991,7 @@ static struct ceph_msg *create_request_message(struct ceph_mds_client *mdsc,
 
 	if (req->r_pagelist) {
 		struct ceph_pagelist *pagelist = req->r_pagelist;
-		atomic_inc(&pagelist->refcnt);
+		refcount_inc(&pagelist->refcnt);
 		ceph_msg_data_add_pagelist(msg, pagelist);
 		msg->hdr.data_len = cpu_to_le32(pagelist->length);
 	} else {

include/linux/ceph/pagelist.h

@@ -2,7 +2,7 @@
 #define __FS_CEPH_PAGELIST_H
 
 #include <asm/byteorder.h>
-#include <linux/atomic.h>
+#include <linux/refcount.h>
 #include <linux/list.h>
 #include <linux/types.h>
 
@@ -13,7 +13,7 @@ struct ceph_pagelist {
 	size_t room;
 	struct list_head free_list;
 	size_t num_pages_free;
-	atomic_t refcnt;
+	refcount_t refcnt;
 };
 
 struct ceph_pagelist_cursor {
@@ -30,7 +30,7 @@ static inline void ceph_pagelist_init(struct ceph_pagelist *pl)
 	pl->room = 0;
 	INIT_LIST_HEAD(&pl->free_list);
 	pl->num_pages_free = 0;
-	atomic_set(&pl->refcnt, 1);
+	refcount_set(&pl->refcnt, 1);
 }
 
 extern void ceph_pagelist_release(struct ceph_pagelist *pl);

net/ceph/pagelist.c

@@ -16,7 +16,7 @@ static void ceph_pagelist_unmap_tail(struct ceph_pagelist *pl)
 
 void ceph_pagelist_release(struct ceph_pagelist *pl)
 {
-	if (!atomic_dec_and_test(&pl->refcnt))
+	if (!refcount_dec_and_test(&pl->refcnt))
 		return;
 	ceph_pagelist_unmap_tail(pl);
 	while (!list_empty(&pl->head)) {