Re: [PATCH] block: fix possible int overflow

["Denis V. Lunev" <den@virtuozzo.com>]

On 11/6/24 10:53, Kevin Wolf wrote:
> [ Cc: qemu-block ]
>
> Am 06.11.2024 um 09:04 hat Dmitry Frolov geschrieben:
>> The sum "cluster_index + count" may overflow uint32_t.
>>
>> Found by Linux Verification Center (linuxtesting.org) with SVACE.
>>
>> Signed-off-by: Dmitry Frolov <frolov@swemel.ru>
> Thanks, applied to the block branch.
>
> While trying to check if this can be triggered in practice, I found this
> line in parallels_fill_used_bitmap():
>
>      s->used_bmap_size = DIV_ROUND_UP(payload_bytes, s->cluster_size);
>
> s->used_bmap_size is unsigned long, payload_bytes is the int64_t result
> of bdrv_getlength() for the image file, which could certainly be made
> more than 4 GB * cluster_size. I think we need an overflow check there,
> too.
>
> When allocate_clusters() calculates new_usedsize, it doesn't seem to
> consider the overflow case either.
>
> Denis, can you take a look?
>
> Kevin
>
We definitely have more places inside the code and I'll take a look.

Speaking about this particular change - this will not work. In general
we should signal corruption when the cluster number is overflowed.
This data would not be accessible due to format restrictions.

Den