linux-kernel - [BUG] drm/amdgpu: possible null-pointer dereference in dce_vXX_0_afmt

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Message-ID: <650a9f72-712c-c5a3-dc4c-1251fb3bb6cd@gmail.com>
Date:   Tue, 10 Aug 2021 17:28:07 +0800
From:   Tuo Li <islituo@...il.com>
To:     alexander.deucher@....com, christian.koenig@....com,
        Xinhui.Pan@....com, airlied@...ux.ie, daniel@...ll.ch,
        evan.quan@....com, luben.tuikov@....com, tzimmermann@...e.de,
        lee.jones@...aro.org, mh12gx2825@...il.com,
        sakari.ailus@...ux.intel.com, zhangqilong3@...wei.com,
        pmladek@...e.com
Cc:     amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        "baijiaju1990@...il.com" <baijiaju1990@...il.com>
Subject: [BUG] drm/amdgpu: possible null-pointer dereference in
 dce_vXX_0_afmt_setmode()

Hello,

Our static analysis tool finds some possible null-pointer dereferences 
in the amdgpu driver in Linux 5.14.0-rc3:

In dce_v10_0.c:
The variable encoder->crtc is checked in:
1591:    if (encoder->crtc)

This indicates that encoder->crtc can be NULL.
Then the function dce_v10_0_audio_set_dto() is called with the argument 
encoder:
1600:    ce_v10_0_audio_set_dto(encoder, mode->clock);

However, encoder->crtc is dereferenced in this function:
1545:    struct amdgpu_crtc *amdgpu_crtc = to_amdgpu_crtc(encoder->crtc);
1559:    tmp = REG_SET_FIELD(tmp, DCCG_AUDIO_DTO_SOURCE, 
DCCG_AUDIO_DTO0_SOURCE_SEL, amdgpu_crtc->crtc_id);

In dce_v11_0.c and dce_v8_0.c, situations are the same.

I am not quite sure whether these possible null-pointer dereferences are 
real and how to fix them if they are real.
Any feedback would be appreciated, thanks!

Reported-by: TOTE Robot <oslab@...nghua.edu.cn>

Best wishes,
Tuo Li