ext4: fix error return from ext4_ext_handle_uninitialized_extents()

Commit 37794732 breaks the return of error codes from
ext4_ext_handle_uninitialized_extents() in ext4_ext_map_blocks().  A
portion of the patch assigns that function's signed integer return
value to an unsigned int.  Consequently, negatively valued error codes
are lost and can be treated as a bogus allocated block count.
Signed-off-by: NEric Whitney <enwlinux@gmail.com>
Signed-off-by: N"Theodore Ts'o" <tytso@mit.edu>
Cc: stable@vger.kernel.org

fs/ext4/extents.c

@@ -4128,7 +4128,7 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,
 	struct ext4_extent newex, *ex, *ex2;
 	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
 	ext4_fsblk_t newblock = 0;
-	int free_on_err = 0, err = 0, depth;
+	int free_on_err = 0, err = 0, depth, ret;
 	unsigned int allocated = 0, offset = 0;
 	unsigned int allocated_clusters = 0;
 	struct ext4_allocation_request ar;
@@ -4189,9 +4189,13 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,
 			if (!ext4_ext_is_uninitialized(ex))
 				goto out;
 
-			allocated = ext4_ext_handle_uninitialized_extents(
+			ret = ext4_ext_handle_uninitialized_extents(
 				handle, inode, map, path, flags,
 				allocated, newblock);
+			if (ret < 0)
+				err = ret;
+			else
+				allocated = ret;
 			goto out3;
 		}
 	}