linux-kernel - Re: [PATCH] usb: acpi: Prevent null pointer dereference in usb_acpi_add_usb4

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Message-ID: <b886efd9-a611-4e0d-86dd-ae88ba53c3f6@rowland.harvard.edu>
Date: Fri, 18 Apr 2025 10:19:22 -0400
From: Alan Stern <stern@...land.harvard.edu>
To: Chenyuan Yang <chenyuan0y@...il.com>
Cc: gregkh@...uxfoundation.org, mathias.nyman@...ux.intel.com,
	mika.westerberg@...ux.intel.com, ribalda@...omium.org,
	rafael.j.wysocki@...el.com, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: acpi: Prevent null pointer dereference in
 usb_acpi_add_usb4_devlink()

On Thu, Apr 17, 2025 at 02:50:32PM -0500, Chenyuan Yang wrote:
> As demonstrated by the fix for update_port_device_state,
> commit 12783c0b9e2c ("usb: core: Prevent null pointer dereference in update_port_device_state"), 
> usb_hub_to_struct_hub() can return NULL in certain scenarios, 
> such as during hub driver unbind or teardown race conditions, 
> even if the underlying usb_device structure exists.

Those are not the conditions addressed by that commit.  The commit was 
specifically meant to handle a bizarre situation created by the lvstest 
driver (a child device added "by hand" after deconfiguring the parent 
hub).

> Plus, all other places that call usb_hub_to_struct_hub() in the same file
> do check for NULL return values.
> 
> If usb_hub_to_struct_hub() returns NULL, the subsequent access to
> hub->ports[udev->portnum - 1] will cause a null pointer dereference.
> 
> Signed-off-by: Chenyuan Yang <chenyuan0y@...il.com>
> Fixes: f1bfb4a6fed6 ("usb: acpi: add device link between tunneled USB3 device and USB4 Host Interface")
> 
> ---
>  drivers/usb/core/usb-acpi.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/usb/core/usb-acpi.c b/drivers/usb/core/usb-acpi.c
> index 935c0efea0b6..ea1ce8beb0cb 100644
> --- a/drivers/usb/core/usb-acpi.c
> +++ b/drivers/usb/core/usb-acpi.c
> @@ -165,6 +165,8 @@ static int usb_acpi_add_usb4_devlink(struct usb_device *udev)
>  		return 0;
>  
>  	hub = usb_hub_to_struct_hub(udev->parent);
> +	if (!hub)
> +		return 0;
>  	port_dev = hub->ports[udev->portnum - 1];

While this test may not be strictly necessary, it doesn't hurt since 
this isn't a hot path.

Acked-by: Alan Stern <stern@...land.harvard.edu>

Alan Stern