linux-kernel - Re: [REGRESSION 5.19] NULL dereference by ucsi

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Date:   Mon, 22 Aug 2022 10:44:26 +0800
From:   Linyu Yuan <quic_linyyuan@...cinc.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Takashi Iwai <tiwai@...e.de>
CC:     <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [REGRESSION 5.19] NULL dereference by ucsi_acpi driver


On 8/21/2022 2:40 AM, Greg Kroah-Hartman wrote:
> On Fri, Aug 19, 2022 at 06:32:43PM +0200, Takashi Iwai wrote:
>> Hi,
>>
>> we've got multiple reports about 5.19 kernel starting crashing after
>> some time, and this turned out to be triggered by ucsi_acpi driver.
>> The details are found in:
>>    https://bugzilla.suse.com/show_bug.cgi?id=1202386
>>
>> The culprit seems to be the commit 87d0e2f41b8c
>>      usb: typec: ucsi: add a common function ucsi_unregister_connectors()
> Adding Heikki to the thread...
>
>>      
>> This commit looks as if it were a harmless cleanup, but this failed in
>> a subtle way.  Namely, in the error scenario, the driver gets an error
>> at ucsi_register_altmodes(), and goes to the error handling to release
>> the resources.  Through this refactoring, the release part was unified
>> to a funciton ucsi_unregister_connectors().  And there, it has a NULL
>> check of con->wq, and it bails out the loop if it's NULL.
>> Meanwhile, ucsi_register_port() itself still calls destroy_workqueue()
>> and clear con->wq at its error path.  This ended up in the leftover
>> power supply device with the uninitialized / cleared device.
>>
>> It was confirmed that the problem could be avoided by a simple
>> revert.
> I'll be glad to revert this now, unless Heikki thinks:
>
>> I guess another fix could be removing the part clearing con->wq, i.e.
>>
>> --- a/drivers/usb/typec/ucsi/ucsi.c
>> +++ b/drivers/usb/typec/ucsi/ucsi.c
>> @@ -1192,11 +1192,6 @@ static int ucsi_register_port(struct ucsi *ucsi, int index)
>>   out_unlock:
>>   	mutex_unlock(&con->lock);
>>   
>> -	if (ret && con->wq) {
>> -		destroy_workqueue(con->wq);
>> -		con->wq = NULL;
>> -	}
>> -
>>   	return ret;
>>   }
>>   
>>
>> ... but it's totally untested and I'm not entirely sure whether it's
>> better.

this part is original code, yes, but when I make the change you mentioned,

as in the function ucsi_unregister_connectors(),  just use con->wq to 
represent which connector initialized previous,

indeed if we clear it in ucsi_register_port(), something will left unclear.

please send a patch to fix it.

I think your change is good.

> that is any better?
>
> thanks,
>
> greg k-h