[PATCH 1/1] drm/radeon: avoid NULL dereference, si_get_vce_clock_voltage

[PATCH 1/1] drm/radeon: avoid NULL dereference, si_get_vce_clock_voltage

[Heinrich Schuchardt]

It does not make sense to check if table is NULL
and afterwards to dereference it without
considering the result.

The inconsistency was indicated by cppcheck.
An actual NULL pointer dereference was not observed.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
---
 drivers/gpu/drm/radeon/si_dpm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/radeon/si_dpm.c b/drivers/gpu/drm/radeon/si_dpm.c
index e6abc09..ba2cf12 100644
--- a/drivers/gpu/drm/radeon/si_dpm.c
+++ b/drivers/gpu/drm/radeon/si_dpm.c
@@ -2962,7 +2962,7 @@ static int si_get_vce_clock_voltage(struct radeon_device *rdev,
 		&rdev->pm.dpm.dyn_state.vce_clock_voltage_dependency_table;
 
 	if (((evclk == 0) && (ecclk == 0)) ||
-	    (table && (table->count == 0))) {
+	    table == NULL || table->count == 0) {
 		*voltage = 0;
 		return 0;
 	}
-- 
2.1.4

Re: [PATCH 1/1] drm/radeon: avoid NULL dereference, si_get_vce_clock_voltage

[Joe Perches]

On Sun, 2016-08-21 at 22:52 +0200, Heinrich Schuchardt wrote:
> It does not make sense to check if table is NULL
> and afterwards to dereference it without
> considering the result.

This makes no sense.

> The inconsistency was indicated by cppcheck.

Perhaps this is a defect in cppcheck?

> An actual NULL pointer dereference was not observed.
[]
> diff --git a/drivers/gpu/drm/radeon/si_dpm.c b/drivers/gpu/drm/radeon/si_dpm.c
[]
> @@ -2962,7 +2962,7 @@ static int si_get_vce_clock_voltage(struct radeon_device *rdev,
>  		&rdev->pm.dpm.dyn_state.vce_clock_voltage_dependency_table;
>  
>  	if (((evclk == 0) && (ecclk == 0)) ||
> -	    (table && (table->count == 0))) {

Here table is only dereferenced if table is non-null

> +	    table == NULL || table->count == 0) {
>  		*voltage = 0;
>  		return 0;
>  	}

Perhaps the unnecessary parentheses can be reduce though.

 	if ((evclk == 0 && ecclk == 0) || (table && table->count == 0)) {

Re: [PATCH 1/1] drm/radeon: avoid NULL dereference, si_get_vce_clock_voltage

[Heinrich Schuchardt]

On 08/21/2016 11:06 PM, Joe Perches wrote:
> On Sun, 2016-08-21 at 22:52 +0200, Heinrich Schuchardt wrote:
>> It does not make sense to check if table is NULL
>> and afterwards to dereference it without
>> considering the result.
> 
> This makes no sense.
> 
>> The inconsistency was indicated by cppcheck.
> 
> Perhaps this is a defect in cppcheck?
> 
>> An actual NULL pointer dereference was not observed.
> []
>> diff --git a/drivers/gpu/drm/radeon/si_dpm.c b/drivers/gpu/drm/radeon/si_dpm.c
> []
>> @@ -2962,7 +2962,7 @@ static int si_get_vce_clock_voltage(struct radeon_device *rdev,
>>  		&rdev->pm.dpm.dyn_state.vce_clock_voltage_dependency_table;
>>  
>>  	if (((evclk == 0) && (ecclk == 0)) ||
>> -	    (table && (table->count == 0))) {
> 
> Here table is only dereferenced if table is non-null
> 
>> +	    table == NULL || table->count == 0) {
>>  		*voltage = 0;
>>  		return 0;
>>  	}
> 
> Perhaps the unnecessary parentheses can be reduce though.
> 
>  	if ((evclk == 0 && ecclk == 0) || (table && table->count == 0)) {
> 
The possible NULL pointer dereference would occur here:

2970        for (i = 0; i < table->count; i++) {

Re: [PATCH 1/1] drm/radeon: avoid NULL dereference, si_get_vce_clock_voltage

[Joe Perches]

On Sun, 2016-08-21 at 23:20 +0200, Heinrich Schuchardt wrote:
> On 08/21/2016 11:06 PM, Joe Perches wrote:
> > On Sun, 2016-08-21 at 22:52 +0200, Heinrich Schuchardt wrote:
> > > 
> > > It does not make sense to check if table is NULL
> > > and afterwards to dereference it without
> > > considering the result.
> > This makes no sense.
> > > The inconsistency was indicated by cppcheck.
> > Perhaps this is a defect in cppcheck?
> > > An actual NULL pointer dereference was not observed.
> > []
> > > diff --git a/drivers/gpu/drm/radeon/si_dpm.c b/drivers/gpu/drm/radeon/si_dpm.c
> > []
> > > @@ -2962,7 +2962,7 @@ static int si_get_vce_clock_voltage(struct radeon_device *rdev,
> > >  		&rdev->pm.dpm.dyn_state.vce_clock_voltage_dependency_table;
> > >  
> > >  	if (((evclk == 0) && (ecclk == 0)) ||
> > > -	    (table && (table->count == 0))) {
> > Here table is only dereferenced if table is non-null
> > > 
> > > +	    table == NULL || table->count == 0) {
> > >  		*voltage = 0;
> > >  		return 0;
> > >  	}
> > Perhaps the unnecessary parentheses can be reduce though.
> > 
> >  	if ((evclk == 0 && ecclk == 0) || (table && table->count == 0)) {
> > 
> The possible NULL pointer dereference would occur here:
> 
> 2970        for (i = 0; i < table->count; i++) {

This still doesn't make any sense as table is known non-null
at line 2961

	struct radeon_vce_clock_voltage_dependency_table *table =
		&rdev->pm.dpm.dyn_state.vce_clock_voltage_dependency_table;

So I now suggest simply removing the test for table.

Perhaps cppcheck can be improved to know about known non-null pointers.