Re: [PATCH] drm/i915/gvt: fix double-free bug in split_2MB_gtt_entry.

[Zheng Hacker]

Hi everyone,
Now the letter is really plain-text now :)
Thanks Greg

Regards,
Zheng Wang

Zheng Hacker <hackerzheng666@xxxxxxxxx> 于2022年9月5日周一 12:47写道：
>
> Hello everyone,
>
> I'm Zheng Wang. I found a potential double-free bug in drivers/gpu/drm/i915/gvt/gtt.c. I haven't been replied for a long time. So I decided to send it to more relavent supporters and developers to help to solve the problem.
>
> Best regards,
> Zheng Wang.
>
> xmzyshypnc <1002992920@xxxxxx> 于2022年9月4日周日 20:32写道：
>>
>> There is a double-free security bug in split_2MB_gtt_entry.
>>
>> Here is a calling chain : ppgtt_populate_spt->ppgtt_populate_shadow_entry->split_2MB_gtt_entry. If intel_gvt_dma_map_guest_page failed, it will call  ppgtt_invalidate_spt, which will finally call ppgtt_free_spt and kfree(spt). But the caller does not notice that, and it will call ppgtt_free_spt again in error path.
>>
>> Fix this by returning the result of ppgtt_invalidate_spt to split_2MB_gtt_entry.
>>
>> Signed-off-by: Zheng Wang <1002992920@xxxxxx>
>> ---
>>  drivers/gpu/drm/i915/gvt/gtt.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/i915/gvt/gtt.c b/drivers/gpu/drm/i915/gvt/gtt.c
>> index ce0eb03709c3..9f14fded8c0c 100644
>> --- a/drivers/gpu/drm/i915/gvt/gtt.c
>> +++ b/drivers/gpu/drm/i915/gvt/gtt.c
>> @@ -1215,7 +1215,7 @@ static int split_2MB_gtt_entry(struct intel_vgpu *vgpu,
>>                 ret = intel_gvt_dma_map_guest_page(vgpu, start_gfn + sub_index,
>>                                                    PAGE_SIZE, &dma_addr);
>>                 if (ret) {
>> -                       ppgtt_invalidate_spt(spt);
>> +                       ret = ppgtt_invalidate_spt(spt);
>>                         return ret;
>>                 }
>>                 sub_se.val64 = se->val64;
>> --
>> 2.25.1
>>