linux-kernel - Re: [PATCH] drm/amdgpu: fix possible null-pointer dereference in amdgpu_ttm_tt

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Date:   Mon, 2 Aug 2021 10:47:24 +0800
From:   Li Tuo <islituo@...il.com>
To:     Christian König <christian.koenig@....com>
Cc:     amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, airlied@...ux.ie,
        linux-media@...r.kernel.org, linaro-mm-sig@...ts.linaro.org,
        Xinhui.Pan@....com, baijiaju1990@...il.com,
        alexander.deucher@....com, Philip.Yang@....com,
        TOTE Robot <oslab@...nghua.edu.cn>, sumit.semwal@...aro.org,
        daniel@...ll.ch, Felix.Kuehling@....com, airlied@...hat.com,
        Oak.Zeng@....com, nirmoy.das@....com, tzimmermann@...e.de
Subject: Re: [PATCH] drm/amdgpu: fix possible null-pointer dereference in
 amdgpu_ttm_tt_populate()

Thanks for your feedback! We will remove the null tests according to 
your advice and prepare a V2 patch.

Best wishes,
Tuo Li

On 2021/8/2 1:19, Christian König wrote:
> Am 31.07.21 um 10:04 schrieb Tuo Li:
>> The variable ttm is assigned to the variable gtt, and the variable gtt
>> is checked in:
>>    if (gtt && gtt->userptr)
>>
>> This indicates that both ttm and gtt can be NULL.
>> If so, a null-pointer dereference will occur:
>>    if (ttm->page_flags & TTM_PAGE_FLAG_SG)
>>
>> Also, some null-pointer dereferences will occur in the function
>> ttm_pool_alloc() which is called in:
>>    return ttm_pool_alloc(&adev->mman.bdev.pool, ttm, ctx);
>>
>> To fix these possible null-pointer dereferences, the function returns
>> -EINVAL when ttm is NULL.
>
> NAK, the NULL test is just a leftover from when the objects where 
> distinct.
>
> Please remove the NULL test instead.
>
> Regards,
> Christian.
>
>>
>> Reported-by: TOTE Robot <oslab@...nghua.edu.cn>
>> Signed-off-by: Tuo Li <islituo@...il.com>
>> ---
>>   drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 5 ++++-
>>   1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c 
>> b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
>> index 3a55f08e00e1..80440f799c09 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
>> @@ -1120,8 +1120,11 @@ static int amdgpu_ttm_tt_populate(struct 
>> ttm_device *bdev,
>>       struct amdgpu_device *adev = amdgpu_ttm_adev(bdev);
>>       struct amdgpu_ttm_tt *gtt = (void *)ttm;
>>   +    if (ttm == NULL)
>> +        return -EINVAL;
>> +
>>       /* user pages are bound by amdgpu_ttm_tt_pin_userptr() */
>> -    if (gtt && gtt->userptr) {
>> +    if (gtt->userptr) {
>>           ttm->sg = kzalloc(sizeof(struct sg_table), GFP_KERNEL);
>>           if (!ttm->sg)
>>               return -ENOMEM;
>