Re: [PATCH v3 03/26] ext4: correct the hole length returned by ext4_map_blocks()

[Luis Henriques]

On Sat 27 Jan 2024 09:58:02 AM +08, Zhang Yi wrote;
<...>
> +static ext4_lblk_t ext4_ext_determine_insert_hole(struct inode *inode,
> +						  struct ext4_ext_path *path,
> +						  ext4_lblk_t lblk)
> +{
> +	ext4_lblk_t hole_start, len;
> +	struct extent_status es;
> +
> +	hole_start = lblk;
> +	len = ext4_ext_find_hole(inode, path, &hole_start);
> +again:
> +	ext4_es_find_extent_range(inode, &ext4_es_is_delayed, hole_start,
> +				  hole_start + len - 1, &es);
> +	if (!es.es_len)
> +		goto insert_hole;
> +
> +	/*
> +	 * There's a delalloc extent in the hole, handle it if the delalloc
> +	 * extent is in front of, behind and straddle the queried range.
> +	 */
> +	if (lblk >= es.es_lblk + es.es_len) {
> +		/*
> +		 * The delalloc extent is in front of the queried range,
> +		 * find again from the queried start block.
> +		 */
> +		len -= lblk - hole_start;
> +		hole_start = lblk;
> +		goto again;

It's looks like it's easy to trigger an infinite loop here using fstest
generic/039.  If I understand it correctly (which doesn't happen as often
as I'd like), this is due to an integer overflow in the 'if' condition,
and should be fixed with the patch below.