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SubjectRe: [PATCH v3] usb: core: Prevent null pointer dereference in update_port_device_state
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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@vger.kernel.org
>> Signed-off-by: Udipto Goswami <quic_ugoswami@quicinc.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

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