1 files changed, 10 insertions, 3 deletions

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index b3d249d6eba7..028a4b8c12cd 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2333,14 +2333,21 @@ static noinline long btrfs_ioctl_clone(struct file *file, unsigned long srcfd,
 
                         if (type == BTRFS_FILE_EXTENT_REG ||
                             type == BTRFS_FILE_EXTENT_PREALLOC) {
+                                /*
+                                 *    a  | --- range to clone ---|  b
+                                 * | ------------- extent ------------- |
+                                 */
+
+                                /* substract range b */
+                                if (key.offset + datal > off + len)
+                                        datal = off + len - key.offset;
+
+                                /* substract range a */
                                 if (off > key.offset) {
                                         datao += off - key.offset;
                                         datal -= off - key.offset;
                                 }
 
-                                if (key.offset + datal > off + len)
-                                        datal = off + len - key.offset;
-
                                 ret = btrfs_drop_extents(trans, inode,
                                                          new_key.offset,
                                                          new_key.offset + datal,