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

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