[PATCH v2] usb: raw-gadget: fix double-free race during UDC unbind and rebind

[Igor Putko <igorpetindev@gmail.com>]

raw-gadget defers endpoint disabling, request freeing, and descriptor
cleanup to dev_free(). However, dev_free() is only called after
dev->count drops to zero in raw_release(), which happens after
usb_gadget_unregister_driver() has already returned.

Once usb_gadget_unregister_driver() finishes, the UDC can be immediately
rebound by another raw_gadget instance. If that new instance enables an
endpoint, it assigns its newly allocated descriptor to ep->ep->desc on
the shared UDC endpoint. When dev_free() from the old instance runs
concurrently, it calls usb_ep_disable() and frees dev->eps[i].ep->desc,
which now belongs to the new instance. The new instance's usb_ep_enable()
subsequently fails with -ESHUTDOWN, and its error path frees the descriptor
again, causing a KASAN double-free.

Tear down active endpoints and requests synchronously in gadget_unbind()
before the UDC can be bound again. Keep the descriptor pointer inside
struct raw_ep and clear ep->ep->desc on error and disable paths so no
dangling pointers are left on the UDC endpoints.

Reported-by: syzbot+b7534c9b380f81a3b4be@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=b7534c9b380f81a3b4be
Fixes: f2c2e717642c ("usb: gadget: add raw-gadget interface")
Signed-off-by: Igor Putko <igorpetindev@gmail.com>
---
v1 -> v2:
- Keep ep0 request handling in dev_free() to avoid any lock recursion.
- Synchronously disable and clean up active endpoints in gadget_unbind()
  to prevent use after UDC unbind.
- Update endpoint cleanup in dev_free() to free raw_ep->desc.
---
---
 drivers/usb/gadget/legacy/raw_gadget.c | 30 ++++++++++++++++++++++----
 1 file changed, 26 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/gadget/legacy/raw_gadget.c b/drivers/usb/gadget/legacy/raw_gadget.c
index 4febf8dac7ca..a6b42679acc7 100644
--- a/drivers/usb/gadget/legacy/raw_gadget.c
+++ b/drivers/usb/gadget/legacy/raw_gadget.c
@@ -141,6 +141,7 @@ struct raw_ep {
 	enum ep_state		state;
 	struct usb_ep		*ep;
 	u8			addr;
+	struct usb_endpoint_descriptor *desc;
 	struct usb_request	*req;
 	bool			urb_queued;
 	bool			disabling;
@@ -223,7 +224,9 @@ static void dev_free(struct kref *kref)
 			continue;
 		usb_ep_disable(dev->eps[i].ep);
 		usb_ep_free_request(dev->eps[i].ep, dev->eps[i].req);
-		kfree(dev->eps[i].ep->desc);
+		kfree(dev->eps[i].desc);
+		dev->eps[i].desc = NULL;
+		dev->eps[i].ep->desc = NULL;
 		dev->eps[i].state = STATE_EP_DISABLED;
 	}
 	kfree(dev);
@@ -328,6 +331,20 @@ static int gadget_bind(struct usb_gadget *gadget,
 static void gadget_unbind(struct usb_gadget *gadget)
 {
 	struct raw_dev *dev = get_gadget_data(gadget);
+	int i;
+
+	if (dev) {
+		for (i = 0; i < dev->eps_num; i++) {
+			if (dev->eps[i].state == STATE_EP_DISABLED)
+				continue;
+			usb_ep_disable(dev->eps[i].ep);
+			usb_ep_free_request(dev->eps[i].ep, dev->eps[i].req);
+			kfree(dev->eps[i].desc);
+			dev->eps[i].desc = NULL;
+			dev->eps[i].ep->desc = NULL;
+			dev->eps[i].state = STATE_EP_DISABLED;
+		}
+	}
 
 	set_gadget_data(gadget, NULL);
 	/* Matches kref_get() in gadget_bind(). */
@@ -886,6 +903,7 @@ static int raw_ioctl_ep_enable(struct raw_dev *dev, unsigned long value)
 		if (ret < 0) {
 			dev_err(&dev->gadget->dev,
 				"fail, usb_ep_enable returned %d\n", ret);
+			ep->ep->desc = NULL;
 			goto out_free;
 		}
 		ep->req = usb_ep_alloc_request(ep->ep, GFP_ATOMIC);
@@ -893,10 +911,12 @@ static int raw_ioctl_ep_enable(struct raw_dev *dev, unsigned long value)
 			dev_err(&dev->gadget->dev,
 				"fail, usb_ep_alloc_request failed\n");
 			usb_ep_disable(ep->ep);
+			ep->ep->desc = NULL;
 			ret = -ENOMEM;
 			goto out_free;
 		}
 		ep->state = STATE_EP_ENABLED;
+		ep->desc = desc;
 		ep->ep->driver_data = ep;
 		ret = i;
 		goto out_unlock;
@@ -962,7 +982,9 @@ static int raw_ioctl_ep_disable(struct raw_dev *dev, unsigned long value)
 
 	spin_lock_irqsave(&dev->lock, flags);
 	usb_ep_free_request(dev->eps[i].ep, dev->eps[i].req);
-	kfree(dev->eps[i].ep->desc);
+	kfree(dev->eps[i].desc);
+	dev->eps[i].desc = NULL;
+	dev->eps[i].ep->desc = NULL;
 	dev->eps[i].state = STATE_EP_DISABLED;
 	dev->eps[i].disabling = false;
 
@@ -1010,7 +1032,7 @@ static int raw_ioctl_ep_set_clear_halt_wedge(struct raw_dev *dev,
 		ret = -EINVAL;
 		goto out_unlock;
 	}
-	if (usb_endpoint_xfer_isoc(dev->eps[i].ep->desc)) {
+	if (usb_endpoint_xfer_isoc(dev->eps[i].desc)) {
 		dev_dbg(&dev->gadget->dev,
 				"fail, can't halt/wedge ISO endpoint\n");
 		ret = -EINVAL;
@@ -1096,7 +1118,7 @@ static int raw_process_ep_io(struct raw_dev *dev, struct usb_raw_ep_io *io,
 		ret = -EBUSY;
 		goto out_unlock;
 	}
-	if (in != usb_endpoint_dir_in(ep->ep->desc)) {
+	if (in != usb_endpoint_dir_in(ep->desc)) {
 		dev_dbg(&dev->gadget->dev, "fail, wrong direction\n");
 		ret = -EINVAL;
 		goto out_unlock;
-- 
2.47.3