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SubjectRe: [PATCH v3] xen/privcmd: fix error exit of privcmd_ioctl_dm_op()
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On 25.08.22 13:58, Jan Beulich wrote:
> On 25.08.2022 13:40, Juergen Gross wrote:
>> --- a/drivers/xen/privcmd.c
>> +++ b/drivers/xen/privcmd.c
>> @@ -581,7 +581,7 @@ static int lock_pages(
>> struct privcmd_dm_op_buf kbufs[], unsigned int num,
>> struct page *pages[], unsigned int nr_pages, unsigned int *pinned)
>> {
>> - unsigned int i;
>> + unsigned int i, off = 0;
>>
>> for (i = 0; i < num; i++) {
>> unsigned int requested;
>> @@ -589,19 +589,23 @@ static int lock_pages(
>>
>> requested = DIV_ROUND_UP(
>> offset_in_page(kbufs[i].uptr) + kbufs[i].size,
>> - PAGE_SIZE);
>> + PAGE_SIZE) - off;
>> if (requested > nr_pages)
>> return -ENOSPC;
>>
>> page_count = pin_user_pages_fast(
>> - (unsigned long) kbufs[i].uptr,
>> + (unsigned long)kbufs[i].uptr + off * PAGE_SIZE,
>> requested, FOLL_WRITE, pages);
>> - if (page_count < 0)
>> - return page_count;
>> + if (page_count <= 0)
>> + return page_count ? : -EFAULT;
>>
>> *pinned += page_count;
>> nr_pages -= page_count;
>> pages += page_count;
>> +
>> + off = requested - page_count;
>> + if (off)
>> + i--;
>> }
>
> Initially I thought this would go wrong only on the 3rd iteration, but
> meanwhile I think it's wrong already on the 2nd. What I think you need
> is
>
> if (page_count < requested)
> i--;
> off += page_count;
>
> or with the i++ from the loop header absorbed here
>
> if (page_count == requested)
> i++;
> off += page_count;
>
> Plus of course off needs resetting to zero whenever i advances. I.e.
>
> if (page_count == requested) {
> i++;
> off = 0;
> } else {
> off += page_count;
> }

Yeah, or:

off = (page_count == requested) ? 0 : off + page_count;
i += !off;


Juergen
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