ceph: avoid a use-after-free in ceph_destroy_options()

syzbot reported a use-after-free in ceph_destroy_options(), called from
ceph_mount().  The problem was that create_fs_client() consumed the opt
pointer on some errors, but not on all of them.  Make sure it always
consumes both libceph and ceph options.

Reported-by: syzbot+8ab6f1042021b4eed062@syzkaller.appspotmail.com
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: "Yan, Zheng" <zyan@redhat.com>

fs/ceph/super.c

@@ -602,6 +602,8 @@ static int extra_mon_dispatch(struct ceph_client *client, struct ceph_msg *msg)
 
 /*
  * create a new fs client
+ *
+ * Success or not, this function consumes @fsopt and @opt.
  */
 static struct ceph_fs_client *create_fs_client(struct ceph_mount_options *fsopt,
 					struct ceph_options *opt)
@@ -609,17 +611,20 @@ static struct ceph_fs_client *create_fs_client(struct ceph_mount_options *fsopt,
 	struct ceph_fs_client *fsc;
 	int page_count;
 	size_t size;
-	int err = -ENOMEM;
+	int err;
 
 	fsc = kzalloc(sizeof(*fsc), GFP_KERNEL);
-	if (!fsc)
-		return ERR_PTR(-ENOMEM);
+	if (!fsc) {
+		err = -ENOMEM;
+		goto fail;
+	}
 
 	fsc->client = ceph_create_client(opt, fsc);
 	if (IS_ERR(fsc->client)) {
 		err = PTR_ERR(fsc->client);
 		goto fail;
 	}
+	opt = NULL; /* fsc->client now owns this */
 
 	fsc->client->extra_mon_dispatch = extra_mon_dispatch;
 	fsc->client->osdc.abort_on_full = true;
@@ -677,6 +682,9 @@ static struct ceph_fs_client *create_fs_client(struct ceph_mount_options *fsopt,
 	ceph_destroy_client(fsc->client);
 fail:
 	kfree(fsc);
+	if (opt)
+		ceph_destroy_options(opt);
+	destroy_mount_options(fsopt);
 	return ERR_PTR(err);
 }
 
@@ -1042,8 +1050,6 @@ static struct dentry *ceph_mount(struct file_system_type *fs_type,
 	fsc = create_fs_client(fsopt, opt);
 	if (IS_ERR(fsc)) {
 		res = ERR_CAST(fsc);
-		destroy_mount_options(fsopt);
-		ceph_destroy_options(opt);
 		goto out_final;
 	}