On Mon, 21 Nov 2022, John Keeping wrote:
65;6999;1c
> On Mon, Nov 21, 2022 at 11:18:34AM -0500, Alan Stern wrote:
> > On Mon, Nov 21, 2022 at 12:38:37PM +0000, John Keeping wrote:
> > > On Sun, Nov 20, 2022 at 03:46:26PM -0500, Alan Stern wrote:
> > > > I see. The solution is simple: Embed a struct device in struct f_hidg,
> > > > and call cdev_device_add() to add the device and the cdev. This will
> > > > automatically make the device the parent of the cdev, so the device's
> > > > refcount won't go to 0 until the cdev's refcount does. Then you can tie
> > > > the f_hidg's lifetime to the device's, so the device's release routine
> > > > can safely deallocate the entire f_hidg structure.
> > > >
> > > > The parent of the new struct device should be set to &gadget->dev. If
> > > > you can't think of a better name for the device, you could simply append
> > > > ":I" to the parent's name, where I is the interface number, or even
> > > > append ":C.I" where C is the config number (like we do on the host
> > > > side).
> > >
> > > There is no gadget->dev at the time struct f_hidg is allocated.
> > >
> > > AFAICT the device is the UDC, which is only associated with the gadget
> > > when it is bound. The functions are allocated earlier than this and I
> > > can't see any device associated with struct usb_function_instance.
> >
> > Ah, that's a shame. All right, so be it.
> >
> > > The patch below does fix the issue, but I'm wondering if there's a
> > > deeper problem here that can only be properly solved by adding some
> > > device/kobject hierarchy to the config side of things.
> >
> > I don't believe there's any deeper problem. If someone wants to have an
> > fhidg device as a child of the gadget, I think it could be added and
> > removed in the ->set_alt() and ->disable() callbacks. Or maybe the
> > ->bind() and ->unbind() callbacks (I've never had to work with configfs
> > so I'm not clear on the details).
>
> It turns out there's already a device being created here, just not
> associated with the structure. Your suggestions around
> cdev_device_add() made me spot what's going on with that so the actual
> fix is to pull its lifetime up to match struct f_hidg.
>
> -- >8 --
> Subject: [PATCH] usb: gadget: f_hid: fix f_hidg lifetime vs cdev
>
> 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.
This is much better, thanks for re-spinning.
> [Also fix refcount leak on an error path.]
>
> Signed-off-by: John Keeping <john@xxxxxxxxxxxx>
> ---
> drivers/usb/gadget/function/f_hid.c | 50 ++++++++++++++++-------------
> 1 file changed, 28 insertions(+), 22 deletions(-)
>
> diff --git a/drivers/usb/gadget/function/f_hid.c b/drivers/usb/gadget/function/f_hid.c
> index ca0a7d9eaa34..0b94668a3812 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);
Could we store/fetch this with dev_{set,get}_drvdata(), and make
hidg->dev a pointer reducing the size of the struct f_hidg.
> + kfree(hidg->set_report_buf);
> + kfree(hidg);
> +}
> +
> /*-------------------------------------------------------------------------*/
> /* 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 +1005,12 @@ 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);
> + cdev_set_parent(&hidg->cdev, &hidg->dev.kobj);
cdev_device_add() should take care of this, so long as:
if (dev->devt)
dev_set_parent(cdev, &dev->kobj);
> + 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 +1241,7 @@ 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);
> + put_device(&hidg->dev);
> mutex_lock(&opts->lock);
> --opts->refcnt;
> mutex_unlock(&opts->lock);
> @@ -1256,8 +1251,7 @@ static void hidg_unbind(struct usb_configuration *c, struct usb_function *f)
> {
> struct f_hidg *hidg = func_to_hidg(f);
>
> - device_destroy(hidg_class, MKDEV(major, hidg->minor));
> - cdev_del(&hidg->cdev);
> + cdev_device_del(&hidg->cdev);
>
> usb_free_all_descriptors(f);
> }
> @@ -1266,6 +1260,7 @@ static struct usb_function *hidg_alloc(struct usb_function_instance *fi)
> {
> struct f_hidg *hidg;
> struct f_hid_opts *opts;
> + int ret;
>
> /* allocate and initialize one new instance */
> hidg = kzalloc(sizeof(*hidg), GFP_KERNEL);
> @@ -1277,17 +1272,28 @@ static struct usb_function *hidg_alloc(struct usb_function_instance *fi)
> mutex_lock(&opts->lock);
> ++opts->refcnt;
>
> - hidg->minor = opts->minor;
> + device_initialize(&hidg->dev);
> + hidg->dev.release = hidg_release;
> + hidg->dev.class = hidg_class;
> + hidg->dev.devt = MKDEV(major, opts->minor);
> + ret = dev_set_name(&hidg->dev, "hidg%d", opts->minor);
> + if (ret) {
> + --opts->refcnt;
Since we're holding the opts lock at this point, is there anything
preventing us from incrementing the refcnt at the end, just before
giving up the lock, thus saving 2 decrements in the error paths?
> + mutex_unlock(&opts->lock);
> + return ERR_PTR(ret);
> + }
> +
> hidg->bInterfaceSubClass = opts->subclass;
> hidg->bInterfaceProtocol = opts->protocol;
> hidg->report_length = opts->report_length;
> hidg->report_desc_length = opts->report_desc_length;
> if (opts->report_desc) {
> - hidg->report_desc = kmemdup(opts->report_desc,
> + hidg->report_desc = devm_kmemdup(&hidg->dev, opts->report_desc,
Nice.
> opts->report_desc_length,
> GFP_KERNEL);
> if (!hidg->report_desc) {
> - kfree(hidg);
> + put_device(&hidg->dev);
> + --opts->refcnt;
> mutex_unlock(&opts->lock);
> return ERR_PTR(-ENOMEM);
> }
Thanks for doing this John, your work is appreciated.
--
Lee Jones [李琼斯]
