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

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Date: Wed, 10 Jan 2024 14:18:02 +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



On 1/9/2024 8:10 PM, Sergei Shtylyov wrote:
> 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...

sure, i'll remove in v4.

Thanks,
-Udipto