On Jul 4, 2022, at 8:27 AM, Lukas Czerner <lczerner@xxxxxxxxxx> wrote:
>
> ext4_append() must always allocate a new block, otherwise we run the
> risk of overwriting existing directory block corrupting the directory
> tree in the process resulting in all manner of problems later on.
>
> Add a sanity check to see if the logical block is already allocated and
> error out if it is.
>
> Signed-off-by: Lukas Czerner <lczerner@xxxxxxxxxx>
Reviewed-by: Andreas Dilger <adilger@xxxxxxxxx>
> ---
> fs/ext4/namei.c | 16 ++++++++++++++++
> 1 file changed, 16 insertions(+)
>
> diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
> index cf460aa4f81d..4af441494e09 100644
> --- a/fs/ext4/namei.c
> +++ b/fs/ext4/namei.c
> @@ -54,6 +54,7 @@ static struct buffer_head *ext4_append(handle_t *handle,
> struct inode *inode,
> ext4_lblk_t *block)
> {
> + struct ext4_map_blocks map;
> struct buffer_head *bh;
> int err;
>
> @@ -63,6 +64,21 @@ static struct buffer_head *ext4_append(handle_t *handle,
> return ERR_PTR(-ENOSPC);
>
> *block = inode->i_size >> inode->i_sb->s_blocksize_bits;
> + map.m_lblk = *block;
> + map.m_len = 1;
> +
> + /*
> + * We're appending new directory block. Make sure the block is not
> + * allocated yet, otherwise we will end up corrupting the
> + * directory.
> + */
> + err = ext4_map_blocks(NULL, inode, &map, 0);
> + if (err < 0)
> + return ERR_PTR(err);
> + if (err) {
> + EXT4_ERROR_INODE(inode, "Logical block already allocated");
> + return ERR_PTR(-EFSCORRUPTED);
> + }
>
> bh = ext4_bread(handle, inode, *block, EXT4_GET_BLOCKS_CREATE);
> if (IS_ERR(bh))
> --
> 2.35.3
>
Cheers, Andreas
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