[PATCH] USB: gadget: Fix use-after-free during usb config switch

jiantao zhang
2022-11-09T14:12:02Z

> In the process of switching USB config from rndis to other config,
> if function gadget->ops->pullup() return an error,it will inevitably
> cause a system panic(use after free).
>
> Analysis as follows:
> =====================================================================
> (1) write /config/usb_gadget/g1/UDC "none" (init.usb.configfs.rc:2)
>
> gether_disconnect+0x2c/0x1f8 (dev->port_usb = NULL)
> rndis_disable+0x4c/0x74
> composite_disconnect+0x74/0xb0
> configfs_composite_disconnect+0x60/0x7c
> usb_gadget_disconnect+0x70/0x124
> usb_gadget_unregister_driver+0xc8/0x1d8
> gadget_dev_desc_UDC_store+0xec/0x1e4
>
> In general, pointer dev->port will be set to null.
> In function usb_gadget_disconnect(),gadget->udc->driver->disconnect()
> will not be called when gadget->ops->pullup() return an error, therefore,
> pointer dev->port will not be set to NULL.
> If pointer dev->port_usb is not null, it will cause an exception of using
> the freed memory in step3.
>
> (2) rm /config/usb_gadget/g1/configs/b.1/f1 (init.usb.configfs.rc:8)
> (f1 -> ../../../../usb_gadget/g1/functions/rndis.gs4)
>
> rndis_deregister+0x28/0x54 (kfree(params))
> rndis_free+0x44/0x7c (kfree(rndis))
> usb_put_function+0x14/0x1c
> config_usb_cfg_unlink+0xc4/0xe0
> configfs_unlink+0x124/0x1c8
> vfs_unlink+0x114/0x1dc
>
> (3) rmdir /config/usb_gadget/g1/functions/rndis.gs4
> (init.usb.configfs.rc:11)
>
> Call trace:
> panic+0x1fc/0x3d0
> die+0x29c/0x2a8
> die_kernel_fault+0x60/0x90
> do_page_fault+0xa8/0x46c
> do_mem_abort+0x3c/0xac
> el1_abort+0x3c/0x58
> el1_sync_handler+0x40/0x78
> el1_sync+0x84/0x140
> 0xffffff801138f880 (params->resp_avail is an illegal function pointer)
> rndis_close+0x28/0x34 (->rndis_indicate_status_msg-> params->resp_avail())
> eth_stop+0x74/0x110 (if dev->port_usb != NULL, call rndis_close)
> __dev_close_many+0x134/0x194
> dev_close_many+0x48/0x194
> rollback_registered_many+0x118/0x814
> unregister_netdevice_queue+0xe0/0x168
> unregister_netdev+0x20/0x30
> gether_cleanup+0x1c/0x38
> rndis_free_inst+0x2c/0x58
> usb_put_function_instance+0x20/0x34
> rndis_attr_release+0xc/0x14
> kref_put+0x74/0xb8
> config_item_put+0x14/0x1c
> configfs_rmdir+0x314/0x374
> vfs_rmdir+0xa4/0x15c
>
> In step3,function pointer params->resp_avail() is a wild pointer
> becase pointer params has been freed in step2.
>
> Free mem stack(in step2):
> usb_put_function -> rndis_free -> rndis_deregister -> kfree(params)
>
> use-after-free stack(in step3):
> eth_stop -> rndis_close -> rndis_signal_disconnect ->
> rndis_indicate_status_msg -> params->resp_avail()
>
> In function eth_stop(), if pointer dev->port_usb is NULL, function
> rndis_close() will not be called.
>
> If gadget->ops->pullup() return an error in step),dev->port_usb will
> not be set to null. So, a panic will be caused in step3.
> =======================================================================
>
> Through above analysis, i think gadget->udc->driver->disconnect() need
> to be called even if gadget->udc->driver->disconnect() return an error.
>
> This reverts commit 0a55187a1ec8c03d0619e7ce41d10fdc39cff036
>
> I think this change is a code optimization, not a solution to specific
> problem. And i think this problem is caused by this change,revert it can
> solve this problem.
>
> Of course, my understanding may be inaccurate.There may be a better
> solution to this problem. If possible, please give some suggestions,
> thanks.
>
> Fixes:<0a55187a1ec8c> (USB: gadget core: Issue ->disconnect()
> callback from usb_gadget_disconnect())
>
> Signed-off-by: Jiantao Zhang <water.zhangjiantao@huawei.com>
> Signed-off-by: TaoXue <xuetao09@huawei.com>
> ---
> drivers/usb/gadget/udc/core.c | 20 +++++++++++---------
> 1 file changed, 11 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/usb/gadget/udc/core.c b/drivers/usb/gadget/udc/core.c
> index c63c0c2cf649..b502b2ac4824 100644
> --- a/drivers/usb/gadget/udc/core.c
> +++ b/drivers/usb/gadget/udc/core.c
> @@ -707,9 +707,6 @@ EXPORT_SYMBOL_GPL(usb_gadget_connect);
> * as a disconnect (when a VBUS session is active). Not all systems
> * support software pullup controls.
> *
> - * Following a successful disconnect, invoke the ->disconnect() callback
> - * for the current gadget driver so that UDC drivers don't need to.
> - *
> * Returns zero on success, else negative errno.
> */
> int usb_gadget_disconnect(struct usb_gadget *gadget)
> @@ -734,13 +731,8 @@ int usb_gadget_disconnect(struct usb_gadget *gadget)
> }
>
> ret = gadget->ops->pullup(gadget, 0);
> - if (!ret) {
> + if (!ret)
> gadget->connected = 0;
> - mutex_lock(&udc_lock);
> - if (gadget->udc->driver)
> - gadget->udc->driver->disconnect(gadget);
> - mutex_unlock(&udc_lock);
> - }
>
> out:
> trace_usb_gadget_disconnect(gadget, ret);
> @@ -1532,6 +1524,11 @@ static void gadget_unbind_driver(struct device *dev)
> kobject_uevent(&udc->dev.kobj, KOBJ_CHANGE);
>
> usb_gadget_disconnect(gadget);
> +
> + mutex_lock(&udc_lock);
> + udc->driver->disconnect(udc->gadget);
> + mutex_unlock(&udc_lock);
> +
> usb_gadget_disable_async_callbacks(udc);
> if (gadget->irq)
> synchronize_irq(gadget->irq);
> @@ -1626,6 +1623,11 @@ static ssize_t soft_connect_store(struct device *dev,
> usb_gadget_connect(udc->gadget);
> } else if (sysfs_streq(buf, "disconnect")) {
> usb_gadget_disconnect(udc->gadget);
> +
> + mutex_lock(&udc_lock);
> + udc->driver->disconnect(udc->gadget);
> + mutex_unlock(&udc_lock);
> +
> usb_gadget_udc_stop(udc);
> } else {
> dev_err(dev, "unsupported command '%s'\n", buf);