Re: [PATCH] usb: usbtest: fix NULL pointer dereference in usbtest_probe

On Wed, Jul 29, 2026 at 09:19:54AM +0000, syzbot wrote:
> From: Aleksandr Nogikh <[email protected]>
> 
> The usbtest driver relies on the driver_info field of the usb_device_id
> structure to hold a pointer to a struct usbtest_info, which contains
> necessary configuration for the device. When a new device ID is dynamically
> added via the sysfs new_id interface without specifying a reference device,
> the driver_info field defaults to 0. When the USB core binds the device
> using this dynamic ID, usbtest_probe() unconditionally casts the 0 to a
> pointer, resulting in a NULL pointer dereference when attempting to access
> the autoconf bitfield (at offset 0xa) of the struct usbtest_info.
> 
> This leads to the following crash:
> 
> Oops: general protection fault, probably for non-canonical address
> 0xdffffc0000000001: 0000 [#1] SMP KASAN NOPTI
> KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
> RIP: 0010:usbtest_probe+0x522/0xcc0 drivers/usb/misc/usbtest.c:2822
> Call Trace:
>  <TASK>
>  usb_probe_interface+0x653/0xc60 drivers/usb/core/driver.c:396
>  call_driver_probe drivers/base/dd.c:-1 [inline]
>  really_probe+0x254/0xae0 drivers/base/dd.c:706
>  __driver_probe_device+0x1e8/0x360 drivers/base/dd.c:868
>  driver_probe_device+0x4f/0x240 drivers/base/dd.c:898
>  __device_attach_driver+0x270/0x410 drivers/base/dd.c:1026
>  bus_for_each_drv+0x258/0x2f0 drivers/base/bus.c:500
>  __device_attach+0x2c4/0x450 drivers/base/dd.c:1098
>  device_initial_probe+0xa1/0xd0 drivers/base/dd.c:1153
>  bus_probe_device+0x12a/0x220 drivers/base/bus.c:620
>  device_add+0x7d7/0xb80 drivers/base/core.c:3772
>  usb_set_configuration+0x1ad8/0x2180 drivers/usb/core/message.c:2268
>  usb_generic_driver_probe+0x8d/0x150 drivers/usb/core/generic.c:250
>  usb_probe_device+0x1c3/0x3b0 drivers/usb/core/driver.c:291
> 
> To fix this, validate that id->driver_info is not NULL before proceeding
> with the probe. If it is NULL, gracefully return -ENODEV. The check is
> placed before any memory allocation to avoid unnecessary work and simplify
> error handling.
> 
> Fixes: 733260ff9c45 ("[PATCH] USB: add dynamic id functionality to USB core")
> Assisted-by: Gemini:gemini-3.5-flash Gemini:gemini-3.1-pro-preview syzbot
> Reported-by: [email protected]
> Closes: https://syzkaller.appspot.com/bug?extid=7e1e5911f9eac50bedc7
> Link: https://syzkaller.appspot.com/ai_job?id=9e476ca5-99d1-47d2-b9d1-f3b501897179
> Signed-off-by: Aleksandr Nogikh <[email protected]>
> 
> ---
> diff --git a/drivers/usb/misc/usbtest.c b/drivers/usb/misc/usbtest.c
> index 98071b25a..6410b3e26 100644
> --- a/drivers/usb/misc/usbtest.c
> +++ b/drivers/usb/misc/usbtest.c
> @@ -2786,10 +2786,13 @@ usbtest_probe(struct usb_interface *intf, const struct usb_device_id *id)
>  	}
>  #endif
>  
> +	info = (struct usbtest_info *) id->driver_info;

Extra space there, right?  Didn't checkpatch catch that?

And this really isn't the proper solution, just don't allow dynamic
binding for this driver.  That should resolve it, right?

thanks,

greg k-h