linux-kernel - Re: [Nouveau] [PATCH][V2] drm/nouveau: perform null check on msto[i] rathern than msto

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Message-ID: <53264562-fddf-8214-859c-0f491b2ca42a@gmail.com>
Date:   Fri, 18 Aug 2017 08:20:41 +1000
From:   Ben Skeggs <skeggsb@...il.com>
To:     Colin Ian King <colin.king@...onical.com>,
        Ilia Mirkin <imirkin@...m.mit.edu>
Cc:     David Airlie <airlied@...ux.ie>,
        "nouveau@...ts.freedesktop.org" <nouveau@...ts.freedesktop.org>,
        kernel-janitors@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        Ben Skeggs <bskeggs@...hat.com>
Subject: Re: [Nouveau] [PATCH][V2] drm/nouveau: perform null check on msto[i]
 rathern than msto

On 08/18/2017 08:16 AM, Colin Ian King wrote:
> On 17/08/17 23:07, Ilia Mirkin wrote:
>> On Thu, Aug 17, 2017 at 6:03 PM, Colin King <colin.king@...onical.com> wrote:
>>> From: Colin Ian King <colin.king@...onical.com>
>>>
>>> The null check on the array msto is incorrect since msto is never
>>> null. The null check should be instead on msto[i] since this is
>>> being dereferenced in the call to drm_mode_connector_attach_encoder.
>>>
>>> Thanks to Emil Velikov for pointing out the mistake in my original
>>> fix and for suggesting the correct fix.
>>>
>>> Detected by CoverityScan, CID#1375915 ("Array compared against 0")
>>>
>>> Fixes: f479c0ba4a17 ("drm/nouveau/kms/nv50: initial support for DP 1.2 multi-stream")
>>> Signed-off-by: Colin Ian King <colin.king@...onical.com>
>>> ---
>>>  drivers/gpu/drm/nouveau/nv50_display.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/gpu/drm/nouveau/nv50_display.c b/drivers/gpu/drm/nouveau/nv50_display.c
>>> index f7b4326a4641..ed444ecd9e85 100644
>>> --- a/drivers/gpu/drm/nouveau/nv50_display.c
>>> +++ b/drivers/gpu/drm/nouveau/nv50_display.c
>>> @@ -3141,7 +3141,7 @@ nv50_mstc_new(struct nv50_mstm *mstm, struct drm_dp_mst_port *port,
>>>         mstc->connector.funcs->reset(&mstc->connector);
>>>         nouveau_conn_attach_properties(&mstc->connector);
>>>
>>> -       for (i = 0; i < ARRAY_SIZE(mstm->msto) && mstm->msto; i++)
>>> +       for (i = 0; i < ARRAY_SIZE(mstm->msto) && mstm->msto[i]; i++)
>>
>> Ben will have to rule on which way is correct, but another
>> interpretation is that it should be
>>
>> for (...; i < ARRAY_SIZE; i++)
>>   if (mstm->msto[i])
>>     do_stuff()
> 
> Yes, I suspect that is a better generic solution top cope with potential
> "holes".
>>
>> I haven't the faintest clue whether the msto array can have "holes" or not.
> 
> Indeed. Let's see what Ben says.
No, there can't be holes here.  I believe the V2 patch to be correct.

Ben.
> 
> 
>>
>>>                 drm_mode_connector_attach_encoder(&mstc->connector, &mstm->msto[i]->encoder);
>>>
>>>         drm_object_attach_property(&mstc->connector.base, dev->mode_config.path_property, 0);
>>> --
>>> 2.11.0
>>>
>> --
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> 
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