ext4: correctly migrate a file with a hole at the beginning

Currently ext4_ind_migrate() doesn't correctly handle a file which
contains a hole at the beginning of the file.  This caused the migration
to be done incorrectly, and then if there is a subsequent following
delayed allocation write to the "hole", this would reclaim the same data
blocks again and results in fs corruption.

  # assmuing 4k block size ext4, with delalloc enabled
  # skip the first block and write to the second block
  xfs_io -fc "pwrite 4k 4k" -c "fsync" /mnt/ext4/testfile

  # converting to indirect-mapped file, which would move the data blocks
  # to the beginning of the file, but extent status cache still marks
  # that region as a hole
  chattr -e /mnt/ext4/testfile

  # delayed allocation writes to the "hole", reclaim the same data block
  # again, results in i_blocks corruption
  xfs_io -c "pwrite 0 4k" /mnt/ext4/testfile
  umount /mnt/ext4
  e2fsck -nf /dev/sda6
  ...
  Inode 53, i_blocks is 16, should be 8.  Fix? no
  ...

Signed-off-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org

1 files changed, 5 insertions, 4 deletions

diff --git a/fs/ext4/migrate.c b/fs/ext4/migrate.c
index 6d8b0c917364..6163ad21cb0e 100644
--- a/fs/ext4/migrate.c
+++ b/fs/ext4/migrate.c
@@ -620,7 +620,7 @@ int ext4_ind_migrate(struct inode *inode)
         struct ext4_inode_info          *ei = EXT4_I(inode);
         struct ext4_extent              *ex;
         unsigned int                    i, len;
-        ext4_lblk_t                     end;
+        ext4_lblk_t                     start, end;
         ext4_fsblk_t                    blk;
         handle_t                        *handle;
         int                             ret;
@@ -659,11 +659,12 @@ int ext4_ind_migrate(struct inode *inode)
                 goto errout;
         }
         if (eh->eh_entries == 0)
-                blk = len = 0;
+                blk = len = start = end = 0;
         else {
                 len = le16_to_cpu(ex->ee_len);
                 blk = ext4_ext_pblock(ex);
-                end = le32_to_cpu(ex->ee_block) + len - 1;
+                start = le32_to_cpu(ex->ee_block);
+                end = start + len - 1;
                 if (end >= EXT4_NDIR_BLOCKS) {
                         ret = -EOPNOTSUPP;
                         goto errout;
@@ -672,7 +673,7 @@ int ext4_ind_migrate(struct inode *inode)
 
         ext4_clear_inode_flag(inode, EXT4_INODE_EXTENTS);
         memset(ei->i_data, 0, sizeof(ei->i_data));
-        for (i=0; i < len; i++)
+        for (i = start; i <= end; i++)
                 ei->i_data[i] = cpu_to_le32(blk++);
         ext4_mark_inode_dirty(handle, inode);
 errout: