Nouveau - Aug 2017 - [PATCH][V2] drm/nouveau: perform null check on msto[i] rathern than msto

From: Colin Ian King <colin.king at canonical.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 at canonical.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++)
 		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

On Thu, Aug 17, 2017 at 6:03 PM, Colin King <colin.king at canonical.com>
wrote:
> From: Colin Ian King <colin.king at canonical.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 at canonical.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()

I haven't the faintest clue whether the msto array can have
"holes" or not.
>                 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
>

On 17/08/17 23:07, Ilia Mirkin wrote:
> On Thu, Aug 17, 2017 at 6:03 PM, Colin King <colin.king at
canonical.com> wrote:
>> From: Colin Ian King <colin.king at canonical.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 at canonical.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.

> 
>>                
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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