[PATCH v3] usb: usbtest: disable dynamic ID support

[Aleksandr Nogikh <nogikh@google.com>]

The usbtest driver relies on the driver_info field of struct usb_device_id
to point to a valid struct usbtest_info descriptor. This structure contains
essential test configurations, such as endpoint addresses and test modes,
which are required during probe.

When a user dynamically adds a new device ID via the sysfs new_id
interface without specifying a reference device, the USB core initializes
driver_info to 0 (NULL). When a matching device is subsequently probed,
usbtest_probe() unconditionally casts driver_info to a struct usbtest_info
pointer and dereferences it, leading to a NULL pointer dereference 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+0x3b9/0x1280 drivers/usb/misc/usbtest.c:2822

Because usbtest strictly requires pre-defined usbtest_info descriptors
to function, dynamic ID binding via sysfs is fundamentally unsupported
for this driver.

Fix this by setting .no_dynamic_id = 1 on usbtest_driver. This instructs
the USB core to skip creating the new_id and remove_id sysfs interfaces
for usbtest, preventing invalid dynamic ID entries from being created.

Cc: stable@vger.kernel.org
Reported-by: syzbot+7e1e5911f9eac50bedc7@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=7e1e5911f9eac50bedc7
Signed-off-by: Aleksandr Nogikh <nogikh@google.com>
---
Changes in v3:
- Cc stable.
- Link to v2: https://lore.kernel.org/r/20260806142511.2337081-1-nogikh@google.com

Changes in v2:
- Disable dynamic IDs via .no_dynamic_id = 1 instead of adding a runtime NULL
  check in probe().
- Link to v1: https://lore.kernel.org/r/2650cf0f-26f9-48b5-b198-e4cb67c59cf0@mail.kernel.org

 drivers/usb/misc/usbtest.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/usb/misc/usbtest.c b/drivers/usb/misc/usbtest.c
index 98071b25ac076..8759df49be287 100644
--- a/drivers/usb/misc/usbtest.c
+++ b/drivers/usb/misc/usbtest.c
@@ -3054,6 +3054,7 @@ static struct usb_driver usbtest_driver = {
 	.disconnect =	usbtest_disconnect,
 	.suspend =	usbtest_suspend,
 	.resume =	usbtest_resume,
+	.no_dynamic_id = 1,
 };
 
 /*-------------------------------------------------------------------------*/
-- 
base-commit: 48a5a7ab8d6ab7090564339e039c421f315de912
-- 
2.55.0.654.g21b8a5bc05-goog