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

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

[Igor Putko]

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 all 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. Additionally, make sure
raw_release() always unregisters the driver if registered, and release
the ep0 request if gadget_bind() encounters an error.

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>
---
 drivers/usb/gadget/legacy/raw_gadget.c | 69 +++++++++++++++++++-------
 1 file changed, 52 insertions(+), 17 deletions(-)

diff --git a/drivers/usb/gadget/legacy/raw_gadget.c b/drivers/usb/gadget/legacy/raw_gadget.c
index 4febf8dac7ca..379351a010f8 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;
@@ -205,7 +206,6 @@ static struct raw_dev *dev_new(void)
 static void dev_free(struct kref *kref)
 {
 	struct raw_dev *dev = container_of(kref, struct raw_dev, count);
-	int i;
 
 	kfree(dev->udc_name);
 	kfree(dev->driver.udc_name);
@@ -218,14 +218,6 @@ static void dev_free(struct kref *kref)
 		usb_ep_free_request(dev->gadget->ep0, dev->req);
 	}
 	raw_event_queue_destroy(&dev->queue);
-	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].ep->desc);
-		dev->eps[i].state = STATE_EP_DISABLED;
-	}
 	kfree(dev);
 }
 
@@ -316,6 +308,12 @@ static int gadget_bind(struct usb_gadget *gadget,
 	ret = raw_queue_event(dev, USB_RAW_EVENT_CONNECT, 0, NULL);
 	if (ret < 0) {
 		dev_err(&gadget->dev, "failed to queue connect event\n");
+		usb_ep_free_request(gadget->ep0, req);
+		spin_lock_irqsave(&dev->lock, flags);
+		dev->req = NULL;
+		dev->gadget = NULL;
+		dev->eps_num = 0;
+		spin_unlock_irqrestore(&dev->lock, flags);
 		set_gadget_data(gadget, NULL);
 		return ret;
 	}
@@ -328,6 +326,43 @@ 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;
+	unsigned long flags;
+
+	if (!dev)
+		return;
+
+	for (i = 0; i < dev->eps_num; i++) {
+		struct raw_ep *ep = &dev->eps[i];
+
+		spin_lock_irqsave(&dev->lock, flags);
+		if (ep->state == STATE_EP_DISABLED) {
+			spin_unlock_irqrestore(&dev->lock, flags);
+			continue;
+		}
+		ep->state = STATE_EP_DISABLED;
+		spin_unlock_irqrestore(&dev->lock, flags);
+
+		usb_ep_disable(ep->ep);
+
+		spin_lock_irqsave(&dev->lock, flags);
+		usb_ep_free_request(ep->ep, ep->req);
+		kfree(ep->desc);
+		ep->desc = NULL;
+		ep->ep->desc = NULL;
+		spin_unlock_irqrestore(&dev->lock, flags);
+	}
+
+	spin_lock_irqsave(&dev->lock, flags);
+	if (dev->req) {
+		if (dev->ep0_urb_queued)
+			usb_ep_dequeue(dev->gadget->ep0, dev->req);
+		usb_ep_free_request(dev->gadget->ep0, dev->req);
+		dev->req = NULL;
+	}
+	dev->gadget = NULL;
+	dev->eps_num = 0;
+	spin_unlock_irqrestore(&dev->lock, flags);
 
 	set_gadget_data(gadget, NULL);
 	/* Matches kref_get() in gadget_bind(). */
@@ -450,10 +485,6 @@ static int raw_release(struct inode *inode, struct file *fd)
 
 	spin_lock_irqsave(&dev->lock, flags);
 	dev->state = STATE_DEV_CLOSED;
-	if (!dev->gadget) {
-		spin_unlock_irqrestore(&dev->lock, flags);
-		goto out_put;
-	}
 	if (dev->gadget_registered)
 		unregister = true;
 	dev->gadget_registered = false;
@@ -469,7 +500,6 @@ static int raw_release(struct inode *inode, struct file *fd)
 		kref_put(&dev->count, dev_free);
 	}
 
-out_put:
 	/* Matches dev_new() in raw_open(). */
 	kref_put(&dev->count, dev_free);
 	return ret;
@@ -886,6 +916,7 @@ 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 +924,12 @@ 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 +995,9 @@ 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 +1045,7 @@ 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 +1131,7 @@ 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

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

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 3 potential issue(s) to consider:
- [Critical] usb: raw-gadget: deadlock and use-after-free in gadget_unbind() ep0 cleanup
- [Critical] usb: raw-gadget: race between gadget_unbind() and endpoint ioctls
- [Low] usb: raw-gadget: unreachable dev->req cleanup left in dev_free()
--

commit a0840cd47b22c347c5350236b13bd1cde724c788
Author: Igor Putko <igorpetindev@gmail.com>

usb: raw-gadget: fix double-free race during UDC unbind and rebind

This patch moves endpoint disabling, request freeing, and descriptor cleanup
from dev_free() into gadget_unbind() so that UDC endpoints are torn down
synchronously before the UDC can be rebound. It also stores the endpoint
descriptor pointer in struct raw_ep and frees the ep0 request on error in
gadget_bind().

> diff --git a/drivers/usb/gadget/legacy/raw_gadget.c b/drivers/usb/gadget/legacy/raw_gadget.c
> index 4febf8dac7ca5..379351a010f82 100644
> --- a/drivers/usb/gadget/legacy/raw_gadget.c
> +++ b/drivers/usb/gadget/legacy/raw_gadget.c
[ ... ]
> @@ -218,14 +218,6 @@ static void dev_free(struct kref *kref)
>  		usb_ep_free_request(dev->gadget->ep0, dev->req);
>  	}

[Severity: Low]
Is the dev->req cleanup in dev_free() still reachable after this change?

dev->req is only allocated in gadget_bind(). If gadget_bind() fails after
setting dev->req, the new error path frees the request and sets dev->req to
NULL. If gadget_bind() succeeds, it takes a reference via
kref_get(&dev->count) that is only dropped in gadget_unbind(), which now also
frees dev->req and sets both dev->req and dev->gadget to NULL before calling
kref_put().

Should the remaining if (dev->req) block in dev_free() be removed as well?

>  	raw_event_queue_destroy(&dev->queue);
> -	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].ep->desc);
> -		dev->eps[i].state = STATE_EP_DISABLED;
> -	}
>  	kfree(dev);
>  }
[ ... ]
> @@ -328,6 +326,43 @@ 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;
> +	unsigned long flags;
> +
> +	if (!dev)
> +		return;
> +
> +	for (i = 0; i < dev->eps_num; i++) {
> +		struct raw_ep *ep = &dev->eps[i];
> +
> +		spin_lock_irqsave(&dev->lock, flags);
> +		if (ep->state == STATE_EP_DISABLED) {
> +			spin_unlock_irqrestore(&dev->lock, flags);
> +			continue;
> +		}
> +		ep->state = STATE_EP_DISABLED;
> +		spin_unlock_irqrestore(&dev->lock, flags);
> +
> +		usb_ep_disable(ep->ep);
> +
> +		spin_lock_irqsave(&dev->lock, flags);
> +		usb_ep_free_request(ep->ep, ep->req);
> +		kfree(ep->desc);
> +		ep->desc = NULL;
> +		ep->ep->desc = NULL;
> +		spin_unlock_irqrestore(&dev->lock, flags);
> +	}

[Severity: Critical]
Can moving endpoint teardown into gadget_unbind() race with concurrent
endpoint ioctls when the UDC is unbound while the raw-gadget file descriptor
is still open (for example via sysfs unbind or usb_del_gadget())?

There appear to be three races with active ioctl calls:

1. In raw_ioctl_ep_disable(), dev->lock is dropped with state still set to
STATE_EP_ENABLED and disabling set to true:

drivers/usb/gadget/legacy/raw_gadget.c:raw_ioctl_ep_disable() {
	...
	dev->eps[i].disabling = true;
	spin_unlock_irqrestore(&dev->lock, flags);

	usb_ep_disable(dev->eps[i].ep);

	spin_lock_irqsave(&dev->lock, flags);
	usb_ep_free_request(dev->eps[i].ep, dev->eps[i].req);
	...
}

Because gadget_unbind() only checks ep->state == STATE_EP_DISABLED and does
not check ep->disabling, won't both gadget_unbind() and
raw_ioctl_ep_disable() call usb_ep_free_request(ep->ep, ep->req) on the same
request?

2. In raw_process_ep_io(), dev->lock is dropped with ep->urb_queued set to
true before queueing or waiting on ep->req:

drivers/usb/gadget/legacy/raw_gadget.c:raw_process_ep_io() {
	...
	ep->urb_queued = true;
	spin_unlock_irqrestore(&dev->lock, flags);

	ret = usb_ep_queue(ep->ep, ep->req, GFP_KERNEL);
	if (ret) {
		dev_err(&dev->gadget->dev,
				"fail, usb_ep_queue returned %d\n", ret);
		...
	}

	ret = wait_for_completion_interruptible(&done);
	if (ret) {
		dev_dbg(&dev->gadget->dev, "wait interrupted\n");
		usb_ep_dequeue(ep->ep, ep->req);
		...
}

Because gadget_unbind() does not check or wait for ep->urb_queued before
freeing ep->req and clearing dev->gadget, can raw_process_ep_io() pass a
freed ep->req to usb_ep_queue() or usb_ep_dequeue(), and dereference a NULL
dev->gadget in dev_err() or dev_dbg()?

3. While gadget_unbind() drops dev->lock around usb_ep_disable(ep->ep),
dev->state is still STATE_DEV_RUNNING, dev->gadget is still non-NULL, and
ep->state has just been set to STATE_EP_DISABLED. If raw_ioctl_ep_enable()
runs during that window, it can re-enable the current endpoint (causing
gadget_unbind() to immediately free the newly allocated ep->req and ep->desc
while leaving ep->state as STATE_EP_ENABLED) or enable an earlier endpoint i
that gadget_unbind() already passed (leaking the new ep->req and ep->desc and
leaving a dangling ep->ep->desc on the UDC endpoint once dev->eps_num is set
to 0).

> +
> +	spin_lock_irqsave(&dev->lock, flags);
> +	if (dev->req) {
> +		if (dev->ep0_urb_queued)
> +			usb_ep_dequeue(dev->gadget->ep0, dev->req);
> +		usb_ep_free_request(dev->gadget->ep0, dev->req);
> +		dev->req = NULL;
> +	}
> +	dev->gadget = NULL;
> +	dev->eps_num = 0;
> +	spin_unlock_irqrestore(&dev->lock, flags);

[Severity: Critical]
Does this ep0 teardown in gadget_unbind() risk a deadlock and use-after-free
when an ep0 transfer is in flight in raw_process_ep0_io()?

First, gadget_unbind() calls usb_ep_dequeue(dev->gadget->ep0, dev->req) while
holding dev->lock. For UDC drivers that give back dequeued requests
synchronously inside their dequeue callback, such as
dummy_dequeue()->dummy_giveback()->usb_gadget_giveback_request(), the
completion handler gadget_ep0_complete() is invoked on the same CPU:

drivers/usb/gadget/legacy/raw_gadget.c:gadget_ep0_complete() {
	struct raw_dev *dev = req->context;
	unsigned long flags;

	spin_lock_irqsave(&dev->lock, flags);
	...
}

Won't gadget_ep0_complete() deadlock trying to acquire dev->lock while
gadget_unbind() already holds it?

Second, for UDC drivers where usb_ep_dequeue() completes asynchronously,
gadget_unbind() immediately calls usb_ep_free_request(dev->gadget->ep0,
dev->req) without waiting for dev->ep0_done, which frees dev->req while the
UDC still owns the request.

Third, dev->ep0_urb_queued is only set while raw_process_ep0_io() has dropped
dev->lock:

drivers/usb/gadget/legacy/raw_gadget.c:raw_process_ep0_io() {
	...
	dev->ep0_urb_queued = true;
	spin_unlock_irqrestore(&dev->lock, flags);

	ret = usb_ep_queue(dev->gadget->ep0, dev->req, GFP_KERNEL);
	if (ret) {
		dev_err(&dev->gadget->dev,
				"fail, usb_ep_queue returned %d\n", ret);
		spin_lock_irqsave(&dev->lock, flags);
		goto out_queue_failed;
	}

	ret = wait_for_completion_interruptible(&dev->ep0_done);
	if (ret) {
		dev_dbg(&dev->gadget->dev, "wait interrupted\n");
		usb_ep_dequeue(dev->gadget->ep0, dev->req);
		wait_for_completion(&dev->ep0_done);
	...
}

If gadget_unbind() runs concurrently, frees dev->req, and sets dev->req and
dev->gadget to NULL, won't raw_process_ep0_io() dereference a NULL
dev->gadget and pass a freed or NULL dev->req to usb_ep_queue() or
usb_ep_dequeue()?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261024183727.42339-1-igorpetindev@gmail.com?part=1

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

[Igor Putko]

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

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

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Critical] usb: raw-gadget: unlocked endpoint teardown in gadget_unbind() causes UAF
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commit 7b3966f708938c8c77f1729ecbafe22aa581cd3b
Author: Igor Putko <igorpetindev@gmail.com>

usb: raw-gadget: fix double-free race during UDC unbind and rebind

This patch moves active endpoint disabling, request freeing, and descriptor
cleanup into gadget_unbind(), and stores the endpoint descriptor pointer in
struct raw_ep to prevent a double-free race when a UDC is unbound and rebound
to a new raw_gadget instance.

> diff --git a/drivers/usb/gadget/legacy/raw_gadget.c b/drivers/usb/gadget/legacy/raw_gadget.c
> index 4febf8dac7ca5..a6b42679acc74 100644
> --- a/drivers/usb/gadget/legacy/raw_gadget.c
> +++ b/drivers/usb/gadget/legacy/raw_gadget.c
[ ... ]
> @@ -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;
> +		}
> +	}

[Severity: Critical]
Can tearing down endpoints here without holding dev->lock or coordinating
with in-flight ioctls cause use-after-free and double-free regressions when
gadget_unbind() is called while /dev/raw-gadget is still open (for example,
via sysfs driver unbind or UDC removal)?

Specifically, it looks like several races can occur in
drivers/usb/gadget/legacy/raw_gadget.c:

1. In raw_ioctl_ep_disable(), dev->lock is dropped around usb_ep_disable()
while dev->eps[i].state is still STATE_EP_ENABLED:

    dev->eps[i].disabling = true;
    spin_unlock_irqrestore(&dev->lock, flags);

    usb_ep_disable(dev->eps[i].ep);

    spin_lock_irqsave(&dev->lock, flags);
    usb_ep_free_request(dev->eps[i].ep, dev->eps[i].req);
    kfree(dev->eps[i].desc);

If gadget_unbind() runs concurrently, it does not check dev->eps[i].disabling
or take dev->lock, so both paths can free dev->eps[i].req and
dev->eps[i].desc.

2. In raw_process_ep_io(), dev->lock is dropped with ep->urb_queued = true
before calling usb_ep_queue(ep->ep, ep->req, GFP_KERNEL) and
usb_ep_dequeue(ep->ep, ep->req). If gadget_unbind() runs concurrently and
calls usb_ep_free_request(dev->eps[i].ep, dev->eps[i].req), wouldn't
raw_process_ep_io() pass a freed ep->req to usb_ep_queue() or
usb_ep_dequeue()?

3. Because gadget_unbind() frees and clears dev->eps[i].desc before setting
dev->eps[i].state = STATE_EP_DISABLED without holding dev->lock (and
raw_ioctl_ep_enable() sets ep->state = STATE_EP_ENABLED before
ep->desc = desc), a concurrent raw_process_ep_io() or
raw_ioctl_ep_set_clear_halt_wedge() holding dev->lock can observe
STATE_EP_ENABLED while ep->desc is already freed or NULL in
usb_endpoint_dir_in(ep->desc) or usb_endpoint_xfer_isoc(dev->eps[i].desc).

4. Since gadget_unbind() resets dev->eps[i].state = STATE_EP_DISABLED while
leaving dev->state as STATE_DEV_RUNNING and dev->gadget non-NULL, can a
subsequent raw_ioctl_ep_enable() on the open file descriptor re-enable
endpoints on the unbound UDC, leaving them to be torn down later in
dev_free() after a new instance has bound?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261024190758.2526-1-igorpetindev@gmail.com?part=1