[PATCH] usb: typec: fix potential NULL dereference

[PATCH] usb: typec: fix potential NULL dereference

[Maxim Korotkov]

The pointer 'adev' was being dereferenced before being checked for NULL
in the 'type_alt mode_enter()' and 'type_alt mode_exit()' functions.
Although this is a hypothetical issue, it's better to move the pointer
assignment after the NULL check to avoid any potential problems.

Found by Linux Verification Center with Svace static analyzer.

Fixes: 8a37d87d72f0 ("usb: typec: Bus type for alternate modes")
Signed-off-by: Maxim Korotkov <korotkov.maxim.s@gmail.com>
---
 drivers/usb/typec/bus.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/typec/bus.c b/drivers/usb/typec/bus.c
index 098f0efaa58d..ae0aca8f33db 100644
--- a/drivers/usb/typec/bus.c
+++ b/drivers/usb/typec/bus.c
@@ -125,13 +125,16 @@ EXPORT_SYMBOL_GPL(typec_altmode_notify);
  */
 int typec_altmode_enter(struct typec_altmode *adev, u32 *vdo)
 {
-	struct altmode *partner = to_altmode(adev)->partner;
-	struct typec_altmode *pdev = &partner->adev;
+	struct altmode *partner;
+	struct typec_altmode *pdev;
 	int ret;
 
 	if (!adev || adev->active)
 		return 0;
 
+	partner = to_altmode(adev)->partner;
+	pdev = &partner->adev;
+
 	if (!pdev->ops || !pdev->ops->enter)
 		return -EOPNOTSUPP;
 
@@ -156,13 +159,15 @@ EXPORT_SYMBOL_GPL(typec_altmode_enter);
  */
 int typec_altmode_exit(struct typec_altmode *adev)
 {
-	struct altmode *partner = to_altmode(adev)->partner;
-	struct typec_altmode *pdev = &partner->adev;
+	struct altmode *partner;
+	struct typec_altmode *pdev;
 	int ret;
 
 	if (!adev || !adev->active)
 		return 0;
 
+	partner = to_altmode(adev)->partner;
+	pdev = &partner->adev;
 	if (!pdev->ops || !pdev->ops->exit)
 		return -EOPNOTSUPP;
 
-- 
2.37.2

Re: [PATCH] usb: typec: fix potential NULL dereference

[Greg Kroah-Hartman]

On Mon, Apr 17, 2023 at 10:50:03PM +0300, Maxim Korotkov wrote:
> The pointer 'adev' was being dereferenced before being checked for NULL
> in the 'type_alt mode_enter()' and 'type_alt mode_exit()' functions.
> Although this is a hypothetical issue, it's better to move the pointer
> assignment after the NULL check to avoid any potential problems.
> 
> Found by Linux Verification Center with Svace static analyzer.
> 
> Fixes: 8a37d87d72f0 ("usb: typec: Bus type for alternate modes")
> Signed-off-by: Maxim Korotkov <korotkov.maxim.s@gmail.com>
> ---
>  drivers/usb/typec/bus.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/usb/typec/bus.c b/drivers/usb/typec/bus.c
> index 098f0efaa58d..ae0aca8f33db 100644
> --- a/drivers/usb/typec/bus.c
> +++ b/drivers/usb/typec/bus.c
> @@ -125,13 +125,16 @@ EXPORT_SYMBOL_GPL(typec_altmode_notify);
>   */
>  int typec_altmode_enter(struct typec_altmode *adev, u32 *vdo)
>  {
> -	struct altmode *partner = to_altmode(adev)->partner;
> -	struct typec_altmode *pdev = &partner->adev;
> +	struct altmode *partner;
> +	struct typec_altmode *pdev;
>  	int ret;
>  
>  	if (!adev || adev->active)
>  		return 0;
>  
> +	partner = to_altmode(adev)->partner;
> +	pdev = &partner->adev;

As you point out, the original code is still fine here, we check before
we actually use these values.

Also, can adev every actually be NULL?  In looking at the code paths, I
can't see how that could happen.

thanks,

greg k-h

Re: [PATCH] usb: typec: fix potential NULL dereference

[Maxim Korotkov]

On 18.04.2023 09:16, Greg Kroah-Hartman wrote:
> On Mon, Apr 17, 2023 at 10:50:03PM +0300, Maxim Korotkov wrote:
>> The pointer 'adev' was being dereferenced before being checked for NULL
>> in the 'type_alt mode_enter()' and 'type_alt mode_exit()' functions.
>> Although this is a hypothetical issue, it's better to move the pointer
>> assignment after the NULL check to avoid any potential problems.
>>
>> Found by Linux Verification Center with Svace static analyzer.
>>
>> Fixes: 8a37d87d72f0 ("usb: typec: Bus type for alternate modes")
>> Signed-off-by: Maxim Korotkov <korotkov.maxim.s@gmail.com>
>> ---
>>   drivers/usb/typec/bus.c | 13 +++++++++----
>>   1 file changed, 9 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/usb/typec/bus.c b/drivers/usb/typec/bus.c
>> index 098f0efaa58d..ae0aca8f33db 100644
>> --- a/drivers/usb/typec/bus.c
>> +++ b/drivers/usb/typec/bus.c
>> @@ -125,13 +125,16 @@ EXPORT_SYMBOL_GPL(typec_altmode_notify);
>>    */
>>   int typec_altmode_enter(struct typec_altmode *adev, u32 *vdo)
>>   {
>> -	struct altmode *partner = to_altmode(adev)->partner;
>> -	struct typec_altmode *pdev = &partner->adev;
>> +	struct altmode *partner;
>> +	struct typec_altmode *pdev;
>>   	int ret;
>>   
>>   	if (!adev || adev->active)
>>   		return 0;
>>   
>> +	partner = to_altmode(adev)->partner;
>> +	pdev = &partner->adev;
> 
> As you point out, the original code is still fine here, we check before
> we actually use these values.
> 
> Also, can adev every actually be NULL?  In looking at the code paths, I
> can't see how that could happen.
> 
> thanks,
> 
> greg k-h

I agree that the adev will most likely never be NULL, but usually this 
pointer is checked before usage (for example in typec_altmode_notify() 
or typec_altmode_vdm()). It is a little odd that in these functions it 
utilized before check. Is it just extra check that can be removed?

best regards, Max

Re: [PATCH] usb: typec: fix potential NULL dereference

[Heikki Krogerus]

On Tue, Apr 18, 2023 at 09:56:51AM +0300, Maxim Korotkov wrote:
> On 18.04.2023 09:16, Greg Kroah-Hartman wrote:
> > On Mon, Apr 17, 2023 at 10:50:03PM +0300, Maxim Korotkov wrote:
> > > The pointer 'adev' was being dereferenced before being checked for NULL
> > > in the 'type_alt mode_enter()' and 'type_alt mode_exit()' functions.
> > > Although this is a hypothetical issue, it's better to move the pointer
> > > assignment after the NULL check to avoid any potential problems.
> > > 
> > > Found by Linux Verification Center with Svace static analyzer.
> > > 
> > > Fixes: 8a37d87d72f0 ("usb: typec: Bus type for alternate modes")
> > > Signed-off-by: Maxim Korotkov <korotkov.maxim.s@gmail.com>
> > > ---
> > >   drivers/usb/typec/bus.c | 13 +++++++++----
> > >   1 file changed, 9 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/drivers/usb/typec/bus.c b/drivers/usb/typec/bus.c
> > > index 098f0efaa58d..ae0aca8f33db 100644
> > > --- a/drivers/usb/typec/bus.c
> > > +++ b/drivers/usb/typec/bus.c
> > > @@ -125,13 +125,16 @@ EXPORT_SYMBOL_GPL(typec_altmode_notify);
> > >    */
> > >   int typec_altmode_enter(struct typec_altmode *adev, u32 *vdo)
> > >   {
> > > -	struct altmode *partner = to_altmode(adev)->partner;
> > > -	struct typec_altmode *pdev = &partner->adev;
> > > +	struct altmode *partner;
> > > +	struct typec_altmode *pdev;
> > >   	int ret;
> > >   	if (!adev || adev->active)
> > >   		return 0;
> > > +	partner = to_altmode(adev)->partner;
> > > +	pdev = &partner->adev;
> > 
> > As you point out, the original code is still fine here, we check before
> > we actually use these values.
> > 
> > Also, can adev every actually be NULL?  In looking at the code paths, I
> > can't see how that could happen.
> > 
> > thanks,
> > 
> > greg k-h
> 
> I agree that the adev will most likely never be NULL, but usually this
> pointer is checked before usage (for example in typec_altmode_notify() or
> typec_altmode_vdm()). It is a little odd that in these functions it utilized
> before check. Is it just extra check that can be removed?

Please go ahead and remove it.

thanks,

-- 
heikki