diff mbox series

usb: typec: fix potential NULL dereference

Message ID 20230417195003.19504-1-korotkov.maxim.s@gmail.com
State New
Headers
Series usb: typec: fix potential NULL dereference |

Commit Message

Maxim Korotkov April 17, 2023, 7:50 p.m. UTC 
  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(-)

Comments

Greg KH April 18, 2023, 6:16 a.m. UTC | #1 
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
Maxim Korotkov April 18, 2023, 6:56 a.m. UTC | #2 
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
Heikki Krogerus April 20, 2023, 8:39 a.m. UTC | #3 
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,
diff mbox series

Patch

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;