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Re: [PATCH] device-tree: fix infinite loop issue in 'assign_shared_memory()'
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Dmytro Prokopchuk1 <dmytro_prokopchuk1@xxxxxxxx>
- Date: Thu, 28 Aug 2025 09:01:28 +0000
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Thu, 28 Aug 2025 09:01:43 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Thread-index: AQHcF/Q482rbLahQD0qhywmRaenDcbR3v1QAgAAFb4A=
- Thread-topic: [PATCH] device-tree: fix infinite loop issue in 'assign_shared_memory()'
On 8/28/25 11:42, Jan Beulich wrote:
> On 28.08.2025 10:17, Dmytro Prokopchuk1 wrote:
>> Resolve infinite loop issue in the 'fail:' cleanup path of the function
>> 'assign_shared_memory()'. The issue was caused by an 'unsigned long' type
>> for the loop counter 'i', which could underflow and wrap around, violating
>> termination conditions.
>> Change 'i' to a signed data type ('long') to ensure safe termination of
>> the 'while (--i >= 0)' loop.
>
> If I was a maintainer of this code, I would strongly object to such a change.
> A signed type variable used as (effectively) an array index is almost always
> conceptually wrong. Plus i continues to be compared to nr_pages, which still
> is of an unsigned type.
>
> What imo wants changing instead is the use of the variable:
>
> fail:
> while ( i-- > 0 )
> put_page_nr(page + i, nr_borrowers);
>
> or yet more simply
>
> fail:
> while ( i-- )
> put_page_nr(page + i, nr_borrowers);
>
> See e.g. prepare_staticmem_pages() for a similar case.
>
> Jan
I had the such thought...
Thanks for advice. I will change it.
Dmytro.
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