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

#syz upstream

On Wed, Jul 29, 2026 at 10:26=E2=80=AFAM 'syzbot' via
syzkaller-upstream-moderation
<[email protected]> wrote:
>
> 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 dynamical=
ly
> added via the sysfs new_id interface without specifying a reference devic=
e,
> 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 acces=
s
> 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 simplif=
y
> error handling.
>
> Fixes: 733260ff9c45 ("[PATCH] USB: add dynamic id functionality to USB co=
re")
> 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=3D7e1e5911f9eac50bedc7
> Link: https://syzkaller.appspot.com/ai_job?id=3D9e476ca5-99d1-47d2-b9d1-f=
3b501897179
> To: "Greg Kroah-Hartman" <[email protected]>
> To: <[email protected]>
> To: "Greg Kroah-Hartman" <[email protected]>
> Cc: "Kees Cook" <[email protected]>
> Cc: <[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 s=
truct usb_device_id *id)
>         }
>  #endif
>
> +       info =3D (struct usbtest_info *) id->driver_info;
> +       if (!info)
> +               return -ENODEV;
> +
>         dev =3D kzalloc_obj(*dev);
>         if (!dev)
>                 return -ENOMEM;
> -       info =3D (struct usbtest_info *) id->driver_info;
>         dev->info =3D info;
>         mutex_init(&dev->lock);
>
>
>
> base-commit: f5098b6bae761e346ebcd9da7f95622c04733cff
> --
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