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Subject: Re: [PATCH v4] usb: core: Prevent null pointer dereference in
 update_port_device_state
To: Udipto Goswami <quic_ugoswami@quicinc.com>,
 Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
 Alan Stern <stern@rowland.harvard.edu>
Cc: Krishna Kurapati <quic_kriskura@quicinc.com>, linux-usb@vger.kernel.org,
 linux-kernel@vger.kernel.org, stable@vger.kernel.org
References: <20240110091422.25347-1-quic_ugoswami@quicinc.com>
From: Sergei Shtylyov <sergei.shtylyov@gmail.com>
Message-ID: <4e272d5d-ec19-7621-1346-4363b0070b1c@gmail.com>
Date: Wed, 10 Jan 2024 12:22:34 +0300
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On 1/10/24 12:14 PM, Udipto Goswami wrote:

> Currently,the function update_port_device_state gets the usb_hub from

   Need space between comma and "the"...

> 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>
[...]

> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> index ffd7c99e24a3..5ba1875e6bf4 100644
> --- a/drivers/usb/core/hub.c
> +++ b/drivers/usb/core/hub.c
> @@ -2053,9 +2053,22 @@ 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 step to unbind the hub before running the rest
> +		 * of the procedure. This triggers hub_disconnect which
> +		 * will set the hub's maxchild to 0, further resulting

   Resulting in.

> +		 * usb_hub_to_struct_hub returning NULL.
> +		 *
> +		 * Add if check to avoid running into NULL pointer
> +		 * de-reference.

   This is obvious from the code below, I think...

> +		 */
> +		if (hub) {
> +			port_dev = hub->ports[udev->portnum - 1];
> +			WRITE_ONCE(port_dev->state, udev->state);
> +			sysfs_notify_dirent(port_dev->state_kn);
> +		}
>  	}
>  }
>  

MBR, Sergey