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    Subject[PATCH 4.1 039/267] ext4: correctly migrate a file with a hole at the beginning
    Date
    4.1-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Eryu Guan <guaneryu@gmail.com>

    commit 8974fec7d72e3e02752fe0f27b4c3719c78d9a15 upstream.

    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>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/ext4/migrate.c | 9 +++++----
    1 file changed, 5 insertions(+), 4 deletions(-)

    --- 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:



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