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

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Date: Thu, 4 Jan 2024 18:35:38 +0530
From: Udipto Goswami <quic_ugoswami@...cinc.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC: Alan Stern <stern@...land.harvard.edu>, <linux-usb@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: core: Prevent null pointer dereference in
 update_port_device_state

Hi Greg,

On 1/4/2024 4:14 PM, Greg Kroah-Hartman wrote:
> On Thu, Jan 04, 2024 at 03:56:16PM +0530, 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.
> 
> Is this true for any real (or fake) hardware?

We saw this in our QCOM hardwares where lvstest.c was calling 
get_dev_desc_store:

	usb_set_device_state+0x128/0x17c
	create_lvs_device+0x60/0xf8 [lvstest]
	get_dev_desc_store+0x94/0x18c [lvstest]
	dev_attr_store+0x30/0x48

I think the part of the test procedure is to first unbind the hub driver 
which calls hub_disconnect setting the maxchild = 0.

So if after this the dev_attr try to access, it throws the NULL pointer 
de-reference.

> 
>>
>> Fix this by introducing an if check after the usb_hub is populated.
>>
>> Fixes: 83cb2604f641 ("usb: core: add sysfs entry for usb device state")
>> Signed-off-by: Udipto Goswami <quic_ugoswami@...cinc.com>
> 
> Any specific reason you don't want this backported to the stable kernels
> that include the commit you marked this as a fix for?
> 
> As my bot says:
> 
> - You have marked a patch with a "Fixes:" tag for a commit that is in an
>    older released kernel, yet you do not have a cc: stable line in the
>    signed-off-by area at all, which means that the patch will not be
>    applied to any older kernel releases.  To properly fix this, please
>    follow the documented rules in the
>    Documentation/process/stable-kernel-rules.rst file for how to resolve
>    this.
Got it, I'll take care of it in next version.

Thanks,
-Udipto