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@xxxxxxxxx>
> > ---
> >   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