linux-kernel - Re: [PATCH 2/2] drm/amd/display: Fix null pointer dereference in error message

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Date:   Wed, 27 Sep 2023 10:15:35 +0800
From:   Cong Liu <liucong2@...inos.cn>
To:     Harry Wentland <harry.wentland@....com>,
        Leo Li <sunpeng.li@....com>,
        Rodrigo Siqueira <Rodrigo.Siqueira@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Aurabindo Pillai <aurabindo.pillai@....com>,
        Tom Chung <chiahsuan.chung@....com>
Cc:     amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] drm/amd/display: Fix null pointer dereference in
 error message


> 
> 
> On 2023-09-26 01:56, Cong Liu wrote:
>> This patch fixes a null pointer dereference in the error message that is
>> printed when the Display Core (DC) fails to initialize. The original
>> message includes the DC version number, which is undefined if the DC is
>> not initialized.
>>
>> Fixes: 9788d087caff ("drm/amd/display: improve the message printed when loading DC")
>> Signed-off-by: Cong Liu <liucong2@...inos.cn>
>> ---
>>   drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 3 +--
>>   1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>> index 8e98dda1e084..bf52a909f558 100644
>> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>> @@ -1703,8 +1703,7 @@ static int amdgpu_dm_init(struct amdgpu_device *adev)
>>   		DRM_INFO("Display Core v%s initialized on %s\n", DC_VER,
>>   			 dce_version_to_string(adev->dm.dc->ctx->dce_version));
>>   	} else {
>> -		DRM_INFO("Display Core v%s failed to initialize on %s\n", DC_VER,
>> -			 dce_version_to_string(adev->dm.dc->ctx->dce_version));
>> +		DRM_INFO("Display Core failed to initialize with v%s!\n", DC_VER);
> 
> There is value in printing the version number. Let's not remove it.
> 
> Instead you can probably fix it by doing a NULL check on adev->dm.dc->ctx.

Hi Harry

I don't understand what you mean. Are you saying that I need to add a 
NULL check in the if statement (i.e. if(adev->dm.dc && 
adev->dm.dc->ctx)), because adev->dm.dc is NULL in the else statement 
and there is no way to print adev->dm.dc->ctx->dce_version.

Regards
Cong

> 
> Harry
> 
>>   		goto error;
>>   	}
>>   
>