Re: [PATCH v2] ext2: Handle fiemap on empty files to prevent EINVAL

[Jan Kara]

On Fri 13-06-25 11:18:38, Wei Gao wrote:
> Previously, ext2_fiemap would unconditionally apply "len = min_t(u64, len,
> i_size_read(inode));", When inode->i_size was 0 (for an empty file), this
> would reduce the requested len to 0. Passing len = 0 to iomap_fiemap could
> then result in an -EINVAL error, even for valid queries on empty files.
> 
> Link: https://github.com/linux-test-project/ltp/issues/1246
> Signed-off-by: Wei Gao <wegao@xxxxxxxx>

...

> diff --git a/fs/ext2/inode.c b/fs/ext2/inode.c
> index 30f8201c155f..591db2b4390a 100644
> --- a/fs/ext2/inode.c
> +++ b/fs/ext2/inode.c
> @@ -895,9 +895,15 @@ int ext2_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
>  		u64 start, u64 len)
>  {
>  	int ret;
> +	u64 i_size;
>  
>  	inode_lock(inode);
> -	len = min_t(u64, len, i_size_read(inode));
> +
> +	i_size = i_size_read(inode);
> +
> +	if (i_size > 0)
> +		len = min_t(u64, len, i_size_read(inode));


Thanks! This would actually lead to excessively slow fiemap for 0-length
files. So what I've ended up with is attached modification of your patch.

> +
>  	ret = iomap_fiemap(inode, fieinfo, start, len, &ext2_iomap_ops);
>  	inode_unlock(inode);
>  
> -- 
> 2.49.0
> 
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
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