linux-kernel - Re: [PATCH] media: dvb-usb: Fix unexpected infinite loop in dvb_usb_read_remote

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Date: Mon, 29 Apr 2024 19:24:21 +0800
From: Zheng Yejian <zhengyejian1@...wei.com>
To: <mchehab@...nel.org>
CC: <linux-media@...r.kernel.org>, <linux-kernel@...r.kernel.org>, Zheng
 Yejian <zhengyejian1@...wei.com>
Subject: Re: [PATCH] media: dvb-usb: Fix unexpected infinite loop in
 dvb_usb_read_remote_control()

On 2024/4/12 21:52, Zheng Yejian wrote:
> Infinite log printing occurs during fuzz test:
> 
>    rc rc1: DViCO FusionHDTV DVB-T USB (LGZ201) as ...
>    ...
>    dvb-usb: schedule remote query interval to 100 msecs.
>    dvb-usb: DViCO FusionHDTV DVB-T USB (LGZ201) successfully initialized ...
>    dvb-usb: bulk message failed: -22 (1/0)
>    dvb-usb: bulk message failed: -22 (1/0)
>    dvb-usb: bulk message failed: -22 (1/0)
>    ...
>    dvb-usb: bulk message failed: -22 (1/0)
> 
> Looking into the codes, there is a loop in dvb_usb_read_remote_control(),
> that is in rc_core_dvb_usb_remote_init() create a work that will call
> dvb_usb_read_remote_control(), and this work will reschedule itself at
> 'rc_interval' intervals to recursively call dvb_usb_read_remote_control(),
> see following code snippet:
> 
>    rc_core_dvb_usb_remote_init() {
>      ...
>      INIT_DELAYED_WORK(&d->rc_query_work, dvb_usb_read_remote_control);
>      schedule_delayed_work(&d->rc_query_work,
>                            msecs_to_jiffies(rc_interval));
>      ...
>    }
> 
>    dvb_usb_read_remote_control() {
>      ...
>      err = d->props.rc.core.rc_query(d);
>      if (err)
>        err(...)  // Did not return even if query failed
>      schedule_delayed_work(&d->rc_query_work,
>                            msecs_to_jiffies(rc_interval));
>    }
> 
> When the infinite log printing occurs, the query callback
> 'd->props.rc.core.rc_query' is cxusb_rc_query(). And the log is due to
> the failure of finding a valid 'generic_bulk_ctrl_endpoint'
> in usb_bulk_msg(), see following code snippet:
> 
>    cxusb_rc_query() {
>      cxusb_ctrl_msg() {
>        dvb_usb_generic_rw() {
>          ret = usb_bulk_msg(d->udev, usb_sndbulkpipe(d->udev,
>                             d->props.generic_bulk_ctrl_endpoint),...);
>          if (ret)
>            err("bulk message failed: %d (%d/%d)",ret,wlen,actlen);
>            ...
>        }
>    ...
>    }
> 
> By analyzing the corresponding USB descriptor, it shows that the
> bNumEndpoints is 0 in its interface descriptor, but
> the 'generic_bulk_ctrl_endpoint' is 1, that means user don't configure
> a valid endpoint for 'generic_bulk_ctrl_endpoint', therefore this
> 'invalid' USB device should be rejected before it calls into
> dvb_usb_read_remote_control().
> 
> To fix it, iiuc, we can add endpoint check in dvb_usb_adapter_init().
> 
> Signed-off-by: Zheng Yejian <zhengyejian1@...wei.com>
> ---
>   drivers/media/usb/dvb-usb/dvb-usb-init.c | 8 ++++++++
>   1 file changed, 8 insertions(+)
> 
> Hi, I'm not very familiar with USB driver, and I'm not sure the
> type check is appropriate or not here. Would be any device properties
> that allow 'generic_bulk_ctrl_endpoint' not being configured, or would
> it be configured late after init ? :)
> 

Kindly ping :)
Hi, Mauro, would you mind taking a look at this code ?

--
Thanks,
Zheng Yejian

> diff --git a/drivers/media/usb/dvb-usb/dvb-usb-init.c b/drivers/media/usb/dvb-usb/dvb-usb-init.c
> index fbf58012becd..48e7b9fb93dd 100644
> --- a/drivers/media/usb/dvb-usb/dvb-usb-init.c
> +++ b/drivers/media/usb/dvb-usb/dvb-usb-init.c
> @@ -104,6 +104,14 @@ static int dvb_usb_adapter_init(struct dvb_usb_device *d, short *adapter_nrs)
>   	 * sometimes a timeout occurs, this helps
>   	 */
>   	if (d->props.generic_bulk_ctrl_endpoint != 0) {
> +		ret = usb_pipe_type_check(d->udev, usb_sndbulkpipe(d->udev,
> +					  d->props.generic_bulk_ctrl_endpoint));
> +		if (ret)
> +			goto frontend_init_err;
> +		ret = usb_pipe_type_check(d->udev, usb_rcvbulkpipe(d->udev,
> +					  d->props.generic_bulk_ctrl_endpoint));
> +		if (ret)
> +			goto frontend_init_err;
>   		usb_clear_halt(d->udev, usb_sndbulkpipe(d->udev, d->props.generic_bulk_ctrl_endpoint));
>   		usb_clear_halt(d->udev, usb_rcvbulkpipe(d->udev, d->props.generic_bulk_ctrl_endpoint));
>   	}