[PATCH v3] usb: raw_gadget: fix use-after-free when UDC is removed

[Anuj Bolewar via B4 Relay <devnull+bolewara.gmail.com@kernel.org>]

From: Anuj Bolewar <bolewara@gmail.com>

When the UDC is removed (e.g. dummy_hcd unbind via sysfs) while the raw
gadget fd is still open, usb_del_gadget() destroys the gadget device
and its name. raw_gadget keeps a dangling pointer in dev->gadget, and
ioctls dereference it after releasing dev->lock, leading to a
use-after-free in dev_err() when usb_ep_queue() fails.

Take a gadget reference in gadget_bind() and drop it in dev_free() so
the gadget device and its name stay alive for as long as the fd is open
and an ioctl may still dereference dev->gadget. gadget_unbind() only
marks the device as failed under dev->lock; the reference is dropped in
dev_free(), which runs only after the fd is closed and no ioctl can be
in flight.

Reported-by: syzbot+9aacea11bc70c3ddaff2@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=9aacea11bc70c3ddaff2
Fixes: f2c2e717642c ("usb: gadget: add raw-gadget interface")
Assisted-by: deepseek:v4-pro
Signed-off-by: Anuj Bolewar <bolewara@gmail.com>
---
The gadget device embedded in the UDC is destroyed when the UDC is
removed while the raw gadget fd is still open (e.g. unbinding dummy_hcd
via sysfs). raw_gadget keeps a dangling pointer in dev->gadget and
ioctls dereference it after dropping dev->lock, which KASAN reports as a
slab use-after-free in raw_process_ep0_io() (dev_err with a freed device
name).

Fix it by holding a gadget reference for the raw device lifetime:
gadget_bind() takes it, gadget_unbind() only marks the device as failed
under dev->lock, and the reference is dropped in dev_free() once the fd
is closed and no ioctl can still be in flight.
---
Changes in v3:
- Use scoped_guard() for the spinlock in gadget_unbind() per review.
- Add Assisted-by trailer per Documentation/process/coding-assistants.rst.
- Link to v2: https://patch.msgid.link/20260804-raw-gadget-ep0-uaf-v2-1-3a5ded46ab50@gmail.com

Changes in v2:
- Reworked per review: the gadget reference is now held for the raw
  device lifetime (bind until dev_free()) instead of the bind/unbind
  window, since ioctls dereference dev->gadget after releasing dev->lock
  and the UDC core owns the gadget's lifetime during bind/unbind.
- gadget_unbind() now only marks the device as failed under dev->lock;
  the reference is dropped in dev_free() after the fd is closed.
- Dropped the now-unneeded comment and switched the spinlock to guard().
- Link to v1: https://patch.msgid.link/20260804-raw-gadget-ep0-uaf-v1-1-07878773da15@gmail.com
---
 drivers/usb/gadget/legacy/raw_gadget.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/gadget/legacy/raw_gadget.c b/drivers/usb/gadget/legacy/raw_gadget.c
index 4febf8dac7c..fb15ab6fc73 100644
--- a/drivers/usb/gadget/legacy/raw_gadget.c
+++ b/drivers/usb/gadget/legacy/raw_gadget.c
@@ -226,6 +226,7 @@ static void dev_free(struct kref *kref)
 		kfree(dev->eps[i].ep->desc);
 		dev->eps[i].state = STATE_EP_DISABLED;
 	}
+	usb_put_gadget(dev->gadget);
 	kfree(dev);
 }
 
@@ -302,7 +303,7 @@ static int gadget_bind(struct usb_gadget *gadget,
 	dev->req = req;
 	dev->req->context = dev;
 	dev->req->complete = gadget_ep0_complete;
-	dev->gadget = gadget;
+	dev->gadget = usb_get_gadget(gadget);
 	gadget_for_each_ep(ep, dev->gadget) {
 		dev->eps[i].ep = ep;
 		dev->eps[i].addr = get_ep_addr(ep->name);
@@ -329,6 +330,8 @@ static void gadget_unbind(struct usb_gadget *gadget)
 {
 	struct raw_dev *dev = get_gadget_data(gadget);
 
+	scoped_guard(spinlock_irqsave, &dev->lock)
+		dev->state = STATE_DEV_FAILED;
 	set_gadget_data(gadget, NULL);
 	/* Matches kref_get() in gadget_bind(). */
 	kref_put(&dev->count, dev_free);

---
base-commit: 075b74841bd0065a3bda3440873c747938e69b68
change-id: 20260804-raw-gadget-ep0-uaf-10a82bdda5bc

Best regards,
--  
Anuj Bolewar <bolewara@gmail.com>