[PATCH] usb: gadget: f_hid: don't call cdev_init while cdev in use

[Michael Zimmermann <sigmaepsilon92@gmail.com>]

When calling unbind, then bind again, cdev_init reinitialized the cdev,
even though there may still be references to it. That's the case when
the /dev/hidg* device is still opened. This obviously unsafe behavior
like oopes.

This fixes this by using cdev_alloc to put the cdev on the heap. That
way, we can simply allocate a new one in hidg_bind.

Closes: https://lore.kernel.org/linux-usb/CAN9vWDKZn0Ts5JyV2_xcAmbnBEi0znMLg_USMFrShRryXrgWGQ@mail.gmail.com/T/#m2cb0dba3633b67b2a679c98499508267d1508881
Signed-off-by: Michael Zimmermann <sigmaepsilon92@gmail.com>
---
 drivers/usb/gadget/function/f_hid.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/drivers/usb/gadget/function/f_hid.c b/drivers/usb/gadget/function/f_hid.c
index 8812ebf33d14..66be2e1282c1 100644
--- a/drivers/usb/gadget/function/f_hid.c
+++ b/drivers/usb/gadget/function/f_hid.c
@@ -106,7 +106,7 @@ struct f_hidg {
 	struct list_head		report_list;
 
 	struct device			dev;
-	struct cdev			cdev;
+	struct cdev			*cdev;
 	struct usb_function		func;
 
 	struct usb_ep			*in_ep;
@@ -749,8 +749,9 @@ static int f_hidg_release(struct inode *inode, struct file *fd)
 
 static int f_hidg_open(struct inode *inode, struct file *fd)
 {
+	struct kobject *parent = inode->i_cdev->kobj.parent;
 	struct f_hidg *hidg =
-		container_of(inode->i_cdev, struct f_hidg, cdev);
+		container_of(parent, struct f_hidg, dev.kobj);
 
 	fd->private_data = hidg;
 
@@ -1285,8 +1286,12 @@ static int hidg_bind(struct usb_configuration *c, struct usb_function *f)
 	}
 
 	/* create char device */
-	cdev_init(&hidg->cdev, &f_hidg_fops);
-	status = cdev_device_add(&hidg->cdev, &hidg->dev);
+	hidg->cdev = cdev_alloc();
+	if (!hidg->cdev)
+		goto fail_free_all;
+	hidg->cdev->ops = &f_hidg_fops;
+
+	status = cdev_device_add(hidg->cdev, &hidg->dev);
 	if (status)
 		goto fail_free_all;
 
@@ -1588,7 +1593,7 @@ static void hidg_unbind(struct usb_configuration *c, struct usb_function *f)
 {
 	struct f_hidg *hidg = func_to_hidg(f);
 
-	cdev_device_del(&hidg->cdev, &hidg->dev);
+	cdev_device_del(hidg->cdev, &hidg->dev);
 	destroy_workqueue(hidg->workqueue);
 	usb_free_all_descriptors(f);
 }
-- 
2.53.0