Re: [PATCH 1/1] zram: reject disksizes that exceed slot index range

[Andrew Morton <akpm@linux-foundation.org>]

On Tue,  4 Aug 2026 22:38:32 +0800 Longlong Xia <xialonglong2025@163.com> wrote:

> From: Longlong Xia <xialonglong@kylinos.cn>
> 
> zram uses u32 slot indexes, while disksize_store() accepts a u64
> size. On 32-bit systems, a disksize larger than U32_MAX pages is
> truncated when zram_meta_alloc() assigns the page count to size_t.
> array_size() then sees only the truncated count, so a small table can
> be allocated while the original capacity is published. Valid I/O
> within that capacity can subsequently access beyond zram->table.
> 
> The same oversized capacity also lets full-device scanners compare a
> u32 index with an upper bound larger than U32_MAX, so the index can
> wrap instead of terminating.
> 
> Reject disksizes larger than U32_MAX pages before aligning and
> allocating the table. This keeps the table size, published capacity and
> slot index range consistent.

Oh.  Rejecting large devices sounds severe.  Can't we just fix the
32-bit trucation issues?

> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -2876,6 +2876,9 @@ static ssize_t disksize_store(struct device *dev, struct device_attribute *attr,
>  		return -EBUSY;
>  	}
>  
> +	if (disksize > (u64)U32_MAX << PAGE_SHIFT)
> +		return -EINVAL;
> +

It would be helpful to have a comment explaining why we're doing this.


AI review appears to have found a similar issue in mark_idle(),
although it could be that your patch accidentally prevents it from
occurring:

	https://sashiko.dev/#/patchset/20260804143832.146129-1-xialonglong2025@163.com