[PATCH 0/2] ext4: fix error handling of failed migration

[Lukas Czerner <lukas@czerner.cz>]

When converting an inode from indirect blocks to extents (the
EXT4_IOC_MIGRATE ioctl) fails, two problems can show up.

ext4_ext_swap_inode_data() can fail after the temporary inode's extent
tree has already been copied into the original inode. The error path
then frees the extent tree blocks via the temporary inode, leaving the
filesystem with multiply claimed blocks. Fix it by resetting the
temporary inode's extent tree and i_blocks right after the copy, so the
cleanup can neither free the original inode's extent tree blocks nor
truncate its data.

Also, ext4_journal_ensure_credits() overwrites whatever error the
migration ran into previously, so the ioctl reports success even though
the migration failed. Use a separate variable for its return value.

Tested with xfstests quick with defaults, home-brewed EXT4_IOC_MIGRATE
stress test and a reproducer written by AI.

Lukas Czerner (2):
  ext4: fix failed migrate freeing extent tree blocks
  ext4: don't lose the error of a failed migration

 fs/ext4/ext4.h    |  1 +
 fs/ext4/extents.c | 11 ++++++++++-
 fs/ext4/migrate.c | 22 ++++++++++++++++++----
 3 files changed, 29 insertions(+), 5 deletions(-)


base-commit: 5b0764a53235d3c77e1ed674e836e1b3fe1a4b1f
-- 
2.56.0