linux-kernel - Re: [PATCH v3] usb: core: Prevent null pointer dereference in update_port_device

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Date: Tue, 9 Jan 2024 17:27:49 +0530
From: Udipto Goswami <quic_ugoswami@...cinc.com>
To: Sergei Shtylyov <sergei.shtylyov@...il.com>,
        Greg Kroah-Hartman
	<gregkh@...uxfoundation.org>,
        Alan Stern <stern@...land.harvard.edu>
CC: Krishna Kurapati <quic_kriskura@...cinc.com>, <linux-usb@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <stable@...r.kernel.org>
Subject: Re: [PATCH v3] usb: core: Prevent null pointer dereference in
 update_port_device_state

Hi Sergei,

On 1/9/2024 3:01 PM, Sergei Shtylyov wrote:
> On 1/9/24 9:17 AM, Udipto Goswami wrote:
> 
>> Currently,the function update_port_device_state gets the usb_hub from
>> udev->parent by calling usb_hub_to_struct_hub.
>> However, in case the actconfig or the maxchild is 0, the usb_hub would
>> be NULL and upon further accessing to get port_dev would result in null
>> pointer dereference.
>>
>> Fix this by introducing an if check after the usb_hub is populated.
>>
>> Fixes: 83cb2604f641 ("usb: core: add sysfs entry for usb device state")
>> Cc: stable@...r.kernel.org
>> Signed-off-by: Udipto Goswami <quic_ugoswami@...cinc.com>
>> ---
>> v3: Re-wrote the comment for better context.
>> v2: Introduced comment for the if check & CC'ed stable.
>>
>>   drivers/usb/core/hub.c | 20 +++++++++++++++++---
>>   1 file changed, 17 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
>> index ffd7c99e24a3..6b514546e59b 100644
>> --- a/drivers/usb/core/hub.c
>> +++ b/drivers/usb/core/hub.c
>> @@ -2053,9 +2053,23 @@ static void update_port_device_state(struct usb_device *udev)
>>   
>>   	if (udev->parent) {
>>   		hub = usb_hub_to_struct_hub(udev->parent);
>> -		port_dev = hub->ports[udev->portnum - 1];
>> -		WRITE_ONCE(port_dev->state, udev->state);
>> -		sysfs_notify_dirent(port_dev->state_kn);
>> +
>> +		/*
>> +		 * The Link Layer Validation System Driver (lvstest)
>> +		 * has procedure of unbinding the hub before running
>> +		 * the rest of the procedure. This triggers
>> +		 * hub_disconnect will set the hub's maxchild to 0.
> 
>     I can't parse this sentence, s/th is missing...
Thanks for the review.
Maybe this would sound better?

"This triggers hub_disconnect which will set hub's maxchild to 0"
> 
>> +		 * This would result usb_hub_to_struct_hub in this
>> +		 * function to return NULL.
> 
>     "This would result in usb_hub_to_struct_hub in this function
> returning NULL", perhaps?

yah sound better. Will take care of it in next version.

Thanks,
-Udipto