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

["syzbot" <syzbot@kernel.org>]

From: Aleksandr Nogikh <nogikh@google.com>

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: syzbot+7e1e5911f9eac50bedc7@syzkaller.appspotmail.com
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 <nogikh@google.com>

---
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;
+	if (!info)
+		return -ENODEV;
+
 	dev = kzalloc_obj(*dev);
 	if (!dev)
 		return -ENOMEM;
-	info = (struct usbtest_info *) id->driver_info;
 	dev->info = info;
 	mutex_init(&dev->lock);
 


base-commit: f5098b6bae761e346ebcd9da7f95622c04733cff
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