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Date: Fri, 3 May 2024 12:51:05 +0100
From: Sean Young <sean@mess.org>
To: Zheng Yejian <zhengyejian1@huawei.com>
Cc: mchehab@kernel.org, linux-kernel@vger.kernel.org,
	linux-media@vger.kernel.org
Subject: Re: [PATCH v2] media: dvb-usb: Fix unexpected infinite loop in
 dvb_usb_read_remote_control()
Message-ID: <ZjTPqR3_EhbNU-fm@gofer.mess.org>
References: <20240412135256.1546051-1-zhengyejian1@huawei.com>
 <20240430104137.1014471-1-zhengyejian1@huawei.com>
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In-Reply-To: <20240430104137.1014471-1-zhengyejian1@huawei.com>

On Tue, Apr 30, 2024 at 06:41:37PM +0800, 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, we need to add endpoint check for 'generic_bulk_ctrl_endpoint'.
> And as Sean suggested, the same check and clear halts should be done for
> 'generic_bulk_ctrl_endpoint_response'. So introduce
> dvb_usb_check_bulk_endpoint() to do it for both of them.
> 
> Fixes: 4d43e13f723e ("V4L/DVB (4643): Multi-input patch for DVB-USB device")
> Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
> ---
>  drivers/media/usb/dvb-usb/dvb-usb-init.c | 27 ++++++++++++++++++++----
>  1 file changed, 23 insertions(+), 4 deletions(-)
> 
> v2:
>  - As Sean suggested, check endpoint and clear halt for both
>    'generic_bulk_ctrl_endpoint' and 'generic_bulk_ctrl_endpoint_response'
>    with the new introduced dvb_usb_check_bulk_endpoint();
>    Link: https://lore.kernel.org/all/ZjCl97Ww6NrzJQCB@gofer.mess.org/
>    Link: https://lore.kernel.org/all/ZjC7rXU7ViaH60_S@gofer.mess.org/
> 
>  - Add Fixes tag.
> 
> v1:
>  - Link: https://lore.kernel.org/all/20240412135256.1546051-1-zhengyejian1@huawei.com/
> 
> diff --git a/drivers/media/usb/dvb-usb/dvb-usb-init.c b/drivers/media/usb/dvb-usb/dvb-usb-init.c
> index fbf58012becd..7eb321bab84f 100644
> --- a/drivers/media/usb/dvb-usb/dvb-usb-init.c
> +++ b/drivers/media/usb/dvb-usb/dvb-usb-init.c
> @@ -23,6 +23,23 @@ static int dvb_usb_force_pid_filter_usage;
>  module_param_named(force_pid_filter_usage, dvb_usb_force_pid_filter_usage, int, 0444);
>  MODULE_PARM_DESC(force_pid_filter_usage, "force all dvb-usb-devices to use a PID filter, if any (default: 0).");
>  
> +static int dvb_usb_check_bulk_endpoint(struct dvb_usb_device *d, u8 endpoint)
> +{
> +	if (endpoint) {
> +		int ret;
> +
> +		ret = usb_pipe_type_check(d->udev, usb_sndbulkpipe(d->udev, endpoint));
> +		if (ret)
> +			return ret;
> +		ret = usb_pipe_type_check(d->udev, usb_rcvbulkpipe(d->udev, endpoint));
> +		if (ret)
> +			return ret;
> +		usb_clear_halt(d->udev, usb_sndbulkpipe(d->udev, endpoint));
> +		usb_clear_halt(d->udev, usb_rcvbulkpipe(d->udev, endpoint));
> +	}
> +	return 0;
> +}
> +
>  static int dvb_usb_adapter_init(struct dvb_usb_device *d, short *adapter_nrs)
>  {
>  	struct dvb_usb_adapter *adap;
> @@ -103,10 +120,12 @@ static int dvb_usb_adapter_init(struct dvb_usb_device *d, short *adapter_nrs)
>  	 * when reloading the driver w/o replugging the device
>  	 * sometimes a timeout occurs, this helps
>  	 */
> -	if (d->props.generic_bulk_ctrl_endpoint != 0) {
> -		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));
> -	}
> +	ret = dvb_usb_check_bulk_endpoint(d, d->props.generic_bulk_ctrl_endpoint);
> +	if (ret)
> +		goto frontend_init_err;
> +	ret = dvb_usb_check_bulk_endpoint(d, d->props.generic_bulk_ctrl_endpoint_response);
> +	if (ret)
> +		goto frontend_init_err;
>  
>  	return 0;

This results in the following warning:

drivers/media/usb/dvb-usb/dvb-usb-init.c:133:9: warning: 'adap' may be used uninitialized [-Wmaybe-uninitialized]

I think these tests should be moved to the top of the function, so no cleanup 
is required.


Sean