On Wed, Nov 23, 2022 at 12:52:24PM +0100, Andrzej Pietrasiewicz wrote:
> Hi John,
>
> W dniu 22.11.2022 o 13:35, John Keeping pisze:
> > The embedded struct cdev does not have its lifetime correctly tied to
> > the enclosing struct f_hidg, so there is a use-after-free if /dev/hidgN
> > is held open while the gadget is deleted.
> >
> > This can readily be replicated with libusbgx's example programs (for
> > conciseness - operating directly via configfs is equivalent):
> >
> > gadget-hid
> > exec 3<> /dev/hidg0
> > gadget-vid-pid-remove
> > exec 3<&-
> >
> > Pull the existing device up in to struct f_hidg and make use of the
> > cdev_device_{add,del}() helpers. This changes the lifetime of the
> > device object to match struct f_hidg, but note that it is still added
> > and deleted at the same time.
> >
> > Fixes: 71adf1189469 ("USB: gadget: add HID gadget driver")
> > Signed-off-by: John Keeping <john@xxxxxxxxxxxx>
> > ---
> > drivers/usb/gadget/function/f_hid.c | 52 ++++++++++++++++-------------
> > 1 file changed, 28 insertions(+), 24 deletions(-)
> >
> > diff --git a/drivers/usb/gadget/function/f_hid.c b/drivers/usb/gadget/function/f_hid.c
> > index ca0a7d9eaa34..8b8bbeaa27cb 100644
> > --- a/drivers/usb/gadget/function/f_hid.c
> > +++ b/drivers/usb/gadget/function/f_hid.c
> > @@ -71,7 +71,7 @@ struct f_hidg {
> > wait_queue_head_t write_queue;
> > struct usb_request *req;
> > - int minor;
> > + struct device dev;
> > struct cdev cdev;
> > struct usb_function func;
> > @@ -84,6 +84,14 @@ static inline struct f_hidg *func_to_hidg(struct usb_function *f)
> > return container_of(f, struct f_hidg, func);
> > }
> > +static void hidg_release(struct device *dev)
> > +{
> > + struct f_hidg *hidg = container_of(dev, struct f_hidg, dev);
> > +
> > + kfree(hidg->set_report_buf);
> > + kfree(hidg);
> > +}
> > +
>
> I assume the above is supposed to free the hidg memory as a result of
> put_device() and you free two things here ...
>
> > /*-------------------------------------------------------------------------*/
> > /* Static descriptors */
> > @@ -904,9 +912,7 @@ static int hidg_bind(struct usb_configuration *c, struct usb_function *f)
> > struct usb_ep *ep;
> > struct f_hidg *hidg = func_to_hidg(f);
> > struct usb_string *us;
> > - struct device *device;
> > int status;
> > - dev_t dev;
> > /* maybe allocate device-global string IDs, and patch descriptors */
> > us = usb_gstrings_attach(c->cdev, ct_func_strings,
> > @@ -999,21 +1005,11 @@ static int hidg_bind(struct usb_configuration *c, struct usb_function *f)
> > /* create char device */
> > cdev_init(&hidg->cdev, &f_hidg_fops);
> > - dev = MKDEV(major, hidg->minor);
> > - status = cdev_add(&hidg->cdev, dev, 1);
> > + status = cdev_device_add(&hidg->cdev, &hidg->dev);
> > if (status)
> > goto fail_free_descs;
> > - device = device_create(hidg_class, NULL, dev, NULL,
> > - "%s%d", "hidg", hidg->minor);
> > - if (IS_ERR(device)) {
> > - status = PTR_ERR(device);
> > - goto del;
> > - }
> > -
> > return 0;
> > -del:
> > - cdev_del(&hidg->cdev);
> > fail_free_descs:
> > usb_free_all_descriptors(f);
> > fail:
> > @@ -1244,9 +1240,7 @@ static void hidg_free(struct usb_function *f)
> > hidg = func_to_hidg(f);
> > opts = container_of(f->fi, struct f_hid_opts, func_inst);
> > - kfree(hidg->report_desc);
> > - kfree(hidg->set_report_buf);
> > - kfree(hidg);
>
> ... while here 3 things used to be freed. What happens to hidg->report_desc?
This switched to devm to simplify error handling in hidg_alloc().
