[PATCH] erofs: ensure m_llen is reset to 0 if metadata is invalid

[Gao Xiang]

On 2024/6/30 02:57, Gao Xiang wrote:
> Sometimes, the on-disk metadata might be invalid due to storage
> failure or other unknown issues.
user interrupts, storage failures, or other unknown causes.

> 
> In that case, z_erofs_map_blocks_iter() may still return a valid
> m_llen while other fields remain invalid (e.g., m_plen can be 0).
> 
> Due to the return value of z_erofs_scan_folio() in some path will
> be ignored on purpose, the following z_erofs_scan_folio() could
> then use the invalid value by accident.
> 
> Let's reset m_llen to 0 to prevent this.
> 
> Signed-off-by: Gao Xiang <hsiangkao at linux.alibaba.com>
> ---
>   fs/erofs/zmap.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/fs/erofs/zmap.c b/fs/erofs/zmap.c
> index 9b248ee5fef2..74d3d7bffcf3 100644
> --- a/fs/erofs/zmap.c
> +++ b/fs/erofs/zmap.c
> @@ -711,6 +711,8 @@ int z_erofs_map_blocks_iter(struct inode *inode, struct erofs_map_blocks *map,
>   
>   	err = z_erofs_do_map_blocks(inode, map, flags);
>   out:
> +	if (err)
> +		map->m_llen = 0;
>   	trace_z_erofs_map_blocks_iter_exit(inode, map, flags, err);
>   	return err;
>   }