ceph: check buffer size in ceph_vxattrcb_layout()

If buffer size is zero, return the size of layout vxattr. If buffer
size is not zero, check if it is large enough for layout vxattr.
Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>

fs/ceph/xattr.c

@@ -64,32 +64,48 @@ static bool ceph_vxattrcb_layout_exists(struct ceph_inode_info *ci)
 }
 
 static size_t ceph_vxattrcb_layout(struct ceph_inode_info *ci, char *val,
-					size_t size)
+				   size_t size)
 {
 	int ret;
 	struct ceph_fs_client *fsc = ceph_sb_to_client(ci->vfs_inode.i_sb);
 	struct ceph_osd_client *osdc = &fsc->client->osdc;
 	s64 pool = ceph_file_layout_pg_pool(ci->i_layout);
 	const char *pool_name;
+	char buf[128];
 
 	dout("ceph_vxattrcb_layout %p\n", &ci->vfs_inode);
 	down_read(&osdc->map_sem);
 	pool_name = ceph_pg_pool_name_by_id(osdc->osdmap, pool);
-	if (pool_name)
-		ret = snprintf(val, size,
-		"stripe_unit=%lld stripe_count=%lld object_size=%lld pool=%s",
+	if (pool_name) {
+		size_t len = strlen(pool_name);
+		ret = snprintf(buf, sizeof(buf),
+		"stripe_unit=%lld stripe_count=%lld object_size=%lld pool=",
 		(unsigned long long)ceph_file_layout_su(ci->i_layout),
 		(unsigned long long)ceph_file_layout_stripe_count(ci->i_layout),
-	        (unsigned long long)ceph_file_layout_object_size(ci->i_layout),
-		pool_name);
-	else
-		ret = snprintf(val, size,
+	        (unsigned long long)ceph_file_layout_object_size(ci->i_layout));
+		if (!size) {
+			ret += len;
+		} else if (ret + len > size) {
+			ret = -ERANGE;
+		} else {
+			memcpy(val, buf, ret);
+			memcpy(val + ret, pool_name, len);
+			ret += len;
+		}
+	} else {
+		ret = snprintf(buf, sizeof(buf),
 		"stripe_unit=%lld stripe_count=%lld object_size=%lld pool=%lld",
 		(unsigned long long)ceph_file_layout_su(ci->i_layout),
 		(unsigned long long)ceph_file_layout_stripe_count(ci->i_layout),
 	        (unsigned long long)ceph_file_layout_object_size(ci->i_layout),
 		(unsigned long long)pool);
-
+		if (size) {
+			if (ret <= size)
+				memcpy(val, buf, ret);
+			else
+				ret = -ERANGE;
+		}
+	}
 	up_read(&osdc->map_sem);
 	return ret;
 }