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

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Date: Tue, 9 Jan 2024 17:40:38 +0300
From: Sergei Shtylyov <sergei.shtylyov@...il.com>
To: Udipto Goswami <quic_ugoswami@...cinc.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

On 1/9/24 2:57 PM, 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"

   That seems parsable. :-)

>>> +         * 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.

   Probably "in this function" should be dropped altogether...

> Thanks,
> -Udipto

MBR, Sergey