Re: [PATCH v2] USB: gadget: Fix use-after-free during usb config switch

[Andy Shevchenko]

On Sat, Nov 12, 2022 at 04:14:27PM +0800, jiantao zhang wrote:
> In the process of switching USB config from rndis to other config,
> if the hardware does not support the ->pullup callback, or the
> hardware encounters a low probability fault, both of them may cause
> the ->pullup callback to fail, which will then cause a system panic
> (use after free).
> 
> The gadget drivers sometimes need to be unloaded regardless of the
> hardware's behavior.
> 
> 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 function usb_gadget_disconnect(),The ->disconnect() callback 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 use-after-free 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
> do_page_fault+0xa8/0x46c
> do_mem_abort+0x3c/0xac
> el1_sync_handler+0x40/0x78
> 0xffffff801138f880    (params->resp_avail is an illegal func 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
> rndis_attr_release+0xc/0x14
> kref_put+0x74/0xb8
> config_item_put+0x14/0x1c
> configfs_rmdir+0x314/0x374

Please, read the Submitting Patches document on how to provide backtraces in
the commit messages and update yours accordingly.

> 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 step1,dev->port_usb will
> not be set to null. So, a panic will be caused in step3.
> =======================================================================

> Fixes:<0a55187a1ec8c> (USB: gadget core: Issue ->disconnect()
> callback from usb_gadget_disconnect())

This is malformed tag. Please, read the Submitting Patches document and fix
this accordingly.

> Signed-off-by: Jiantao Zhang <water.zhangjiantao@xxxxxxxxxx>
> Signed-off-by: TaoXue <xuetao09@xxxxxxxxxx>
> ---
>  V1 -> V2: V1 will affect the original function, V2 just move the callback
> after "if" statement, so that the original function will  not be affected.
> And fixed formatting issues.
> 
>  drivers/usb/gadget/udc/core.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/usb/gadget/udc/core.c b/drivers/usb/gadget/udc/core.c
> index c63c0c2cf649..bf9878e1a72a 100644
> --- a/drivers/usb/gadget/udc/core.c
> +++ b/drivers/usb/gadget/udc/core.c
> @@ -734,13 +734,13 @@ 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);
> -	}
> +
> +	mutex_lock(&udc_lock);
> +	if (gadget->udc->driver)
> +		gadget->udc->driver->disconnect(gadget);
> +	mutex_unlock(&udc_lock);
>   out:
>  	trace_usb_gadget_disconnect(gadget, ret);
> -- 
> 2.17.1
> 
> 

-- 
With Best Regards,
Andy Shevchenko