Re:Re: [PATCH] tty: vcc: add check for mdesc_grab()

["Liang He" <windhl@126.com>]

At 2023-03-15 14:32:54, "Greg KH" <gregkh@linuxfoundation.org> wrote:
>On Wed, Mar 15, 2023 at 02:11:21PM +0800, Liang He wrote:
>> In vcc_probe(), we should check the return value of
>> mdesc_grab() as it may return NULL. While the
>> vio_vdev_node() has the NULL-check, but if there
>> is still a call to mdesc_release() which may cause
>> a NPD bug.
>
>Have you actually triggered this issue?  If so, how?
>

Hi, Greg,
Thanks very much for your reply.

In fact, I have not actually triggered this issue, 
but I indeed meet lots of checks in other *_init functions, e.g., mdesc_adi_init()/ldc_init().

However, if we can make sure the return value can never be NULL 
when our kernel execute into these *_probe functions, my patchs are indeed useless.

Thanks and sorry for any potential trouble.

Liang 

>> Fixes: 5d171050e28f ("sparc64: vcc: Enable VCC port probe and removal")
>> Signed-off-by: Liang He <windhl@126.com>
>> ---
>>  drivers/tty/vcc.c | 3 +++
>>  1 file changed, 3 insertions(+)
>> 
>> diff --git a/drivers/tty/vcc.c b/drivers/tty/vcc.c
>> index 34ba6e54789a..e3ba63d0a91f 100644
>> --- a/drivers/tty/vcc.c
>> +++ b/drivers/tty/vcc.c
>> @@ -610,6 +610,9 @@ static int vcc_probe(struct vio_dev *vdev, const struct vio_device_id *id)
>>  
>>  	hp = mdesc_grab();
>>  
>> +	if (!hp)
>> +		return -ENODEV;
>
>This change is obviously not correct and has not been tested, sorry.
>Please do not make changes like this without properly validating them.
>
>greg k-h