linux-kernel - Re: [PATCH] dpu1: dpu_encoder: fix a missing check on list iterator

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Message-ID: <7e0592bc-1e8f-0981-cea2-f74402ab5886@linaro.org>
Date:   Mon, 11 Apr 2022 04:20:12 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Xiaomeng Tong <xiam0nd.tong@...il.com>, robdclark@...il.com,
        sean@...rly.run, airlied@...ux.ie, daniel@...ll.ch
Cc:     quic_abhinavk@...cinc.com, swboyd@...omium.org,
        bjorn.andersson@...aro.org, quic_khsieh@...cinc.com,
        quic_kalyant@...cinc.com, markyacoub@...gle.com,
        jsanka@...eaurora.org, linux-arm-msm@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] dpu1: dpu_encoder: fix a missing check on list iterator

On 11/04/2022 03:56, Dmitry Baryshkov wrote:
> On 27/03/2022 10:32, Xiaomeng Tong wrote:
>> The bug is here:
>>      cstate = to_dpu_crtc_state(drm_crtc->state);
>>
>> For the drm_for_each_crtc(), just like list_for_each_entry(),
>> the list iterator 'drm_crtc' will point to a bogus position
>> containing HEAD if the list is empty or no element is found.
>> This case must be checked before any use of the iterator,
>> otherwise it will lead to a invalid memory access.
>>
>> To fix this bug, use a new variable 'iter' as the list iterator,
>> while use the origin variable 'drm_crtc' as a dedicated pointer
>> to point to the found element.
>>
>> Cc: stable@...r.kernel.org
>> Fixes: b107603b4ad0f ("drm/msm/dpu: map mixer/ctl hw blocks in encoder 
>> modeset")
>> Signed-off-by: Xiaomeng Tong <xiam0nd.tong@...il.com>
> 
> Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>

On the other hand, this code has been removed in 5.18-rc1 in the commit 
764332bf96244cbc8baf08aa35844b29106da312.

> 
>> ---
>>   drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c | 11 ++++++++---
>>   1 file changed, 8 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c 
>> b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
>> index 1e648db439f9..d3fdb18e96f9 100644
>> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
>> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
>> @@ -965,7 +965,7 @@ static void dpu_encoder_virt_mode_set(struct 
>> drm_encoder *drm_enc,
>>       struct dpu_kms *dpu_kms;
>>       struct list_head *connector_list;
>>       struct drm_connector *conn = NULL, *conn_iter;
>> -    struct drm_crtc *drm_crtc;
>> +    struct drm_crtc *drm_crtc = NULL, *iter;
>>       struct dpu_crtc_state *cstate;
>>       struct dpu_global_state *global_state;
>>       struct dpu_hw_blk *hw_pp[MAX_CHANNELS_PER_ENC];
>> @@ -1007,9 +1007,14 @@ static void dpu_encoder_virt_mode_set(struct 
>> drm_encoder *drm_enc,
>>           return;
>>       }
>> -    drm_for_each_crtc(drm_crtc, drm_enc->dev)
>> -        if (drm_crtc->state->encoder_mask & drm_encoder_mask(drm_enc))
>> +    drm_for_each_crtc(iter, drm_enc->dev)
>> +        if (iter->state->encoder_mask & drm_encoder_mask(drm_enc)) {
>> +            drm_crtc = iter;
>>               break;
>> +        }
>> +
>> +    if (!drm_crtc)
>> +        return;
>>       /* Query resource that have been reserved in atomic check step. */
>>       num_pp = dpu_rm_get_assigned_resources(&dpu_kms->rm, global_state,
> 
> 


-- 
With best wishes
Dmitry