Re: [PATCH] btrfs: check file extent backref offset underflow

[Li Zefan <lizf@cn.fujitsu.com>]

Yan, Zheng wrote:
> Offset field in data extent backref can underflow if clone range ioctl
> is used. We can reliably detect the underflow because max file size is
> limited to 2^63 and max data extent size is limited by block group size.
> 
> Signed-off-by: Zheng Yan  <zheng.z.yan@intel.com>

Tested-by: Li Zefan <lizf@cn.fujitsu.com>

...
> @@ -3323,8 +3323,11 @@ static int find_data_references(struct reloc_control *rc,
>  	}
>  
>  	key.objectid = ref_objectid;
> -	key.offset = ref_offset;
>  	key.type = BTRFS_EXTENT_DATA_KEY;
> +	if (ref_offset > ((u64)-1 << 32))
> +		key.offset = 0;
> +	else
> +		key.offset = ref_offset;

This needs comment, as we're working around a corner case and a magic number is
used.

>  
>  	path->search_commit_root = 1;
>  	path->skip_locking = 1;
> --