Re: [PATCH v2] virtio-blk: clamp zone report to the report buffer capacity

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Sun, Jun 07, 2026 at 08:48:34AM -0400, Michael Bommarito wrote:
> virtblk_report_zones() trusts the device-reported number of zones when
> walking the report buffer:
> 
> 	nz = min_t(u64, virtio64_to_cpu(vblk->vdev, report->nr_zones),
> 		   nr_zones);
> 	...
> 	for (i = 0; i < nz && zone_idx < nr_zones; i++) {
> 		ret = virtblk_parse_zone(vblk, &report->zones[i], ...);
> 
> The buffer is allocated by virtblk_alloc_report_buffer(), whose size is
> capped by the queue's max hardware sectors and max segments and can
> therefore hold fewer descriptors than nr_zones. nz is bounded only by
> the device-supplied report->nr_zones and the requested nr_zones, never
> by the buffer's descriptor capacity. At probe time the request count is
> unbounded (blk_revalidate_disk_zones() calls report_zones() with
> nr_zones == UINT_MAX), so the device-supplied report->nr_zones is the
> sole gate: a device that reports more zones than fit in the buffer
> drives the loop to read report->zones[i] past the end of the allocation.
> 
> A malicious or buggy virtio-blk device that reports an inflated nr_zones
> triggers this during zone revalidation at probe. KASAN reports a
> vmalloc-out-of-bounds read in virtblk_report_zones() against the report
> buffer allocated a few lines earlier.
> 
> Clamp nz to the number of descriptors that actually fit in the report
> buffer.
> 
> Fixes: 95bfec41bd3d ("virtio-blk: add support for zoned block devices")
> Assisted-by: Claude:claude-opus-4-8
> Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
> ---
> v2: drop the explanatory comment per Michael S. Tsirkin's review; the
>     clamp itself is unchanged.
> 
>  drivers/block/virtio_blk.c | 2 ++
>  1 file changed, 2 insertions(+)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

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