linux-kernel - Re: [PATCH] media: mxl111sf: change mutex

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Message-ID: <20210815083755.GA1827@gofer.mess.org>
Date:   Sun, 15 Aug 2021 09:37:55 +0100
From:   Sean Young <sean@...s.org>
To:     Pavel Skripkin <paskripkin@...il.com>
Cc:     mkrufky@...uxtv.org, mchehab@...nel.org, crope@....fi,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzbot+5ca0bf339f13c4243001@...kaller.appspotmail.com
Subject: Re: [PATCH] media: mxl111sf: change mutex_init() location

On Sat, Jul 31, 2021 at 12:38:29AM +0300, Pavel Skripkin wrote:
> Syzbot reported, that mxl111sf_ctrl_msg() uses uninitialized
> mutex. The problem was in wrong mutex_init() location.
> 
> Previous mutex_init(&state->msg_lock) call was in ->init() function, but
> dvb_usbv2_init() has this order of calls:
> 
> 	dvb_usbv2_init()
> 	  dvb_usbv2_adapter_init()
> 	    dvb_usbv2_adapter_frontend_init()
> 	      props->frontend_attach()
> 
> 	  props->init()
> 
> Since mxl111sf_frontend_attach_atsc_mh() calls mxl111sf_ctrl_msg()
> internally we need to initialize state->msg_lock in it to make lockdep
> happy.

What about the other frontends like mxl111sf_frontend_attach_dvbt? They
no longer initialize the mutex.

Thanks

Sean

> 
> Reported-and-tested-by: syzbot+5ca0bf339f13c4243001@...kaller.appspotmail.com
> Fixes: 8572211842af ("[media] mxl111sf: convert to new DVB USB")
> Signed-off-by: Pavel Skripkin <paskripkin@...il.com>
> ---
>  drivers/media/usb/dvb-usb-v2/mxl111sf.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/media/usb/dvb-usb-v2/mxl111sf.c b/drivers/media/usb/dvb-usb-v2/mxl111sf.c
> index 7865fa0a8295..2e5663ffa7ce 100644
> --- a/drivers/media/usb/dvb-usb-v2/mxl111sf.c
> +++ b/drivers/media/usb/dvb-usb-v2/mxl111sf.c
> @@ -931,8 +931,6 @@ static int mxl111sf_init(struct dvb_usb_device *d)
>  		  .len = sizeof(eeprom), .buf = eeprom },
>  	};
>  
> -	mutex_init(&state->msg_lock);
> -
>  	ret = get_chip_info(state);
>  	if (mxl_fail(ret))
>  		pr_err("failed to get chip info during probe");
> @@ -979,8 +977,12 @@ static int mxl111sf_frontend_attach_mh(struct dvb_usb_adapter *adap)
>  static int mxl111sf_frontend_attach_atsc_mh(struct dvb_usb_adapter *adap)
>  {
>  	int ret;
> +	struct mxl111sf_state *state = d_to_priv(adap_to_d(adap));
> +
>  	pr_debug("%s\n", __func__);
>  
> +	mutex_init(&state->msg_lock);
> +
>  	ret = mxl111sf_lgdt3305_frontend_attach(adap, 0);
>  	if (ret < 0)
>  		return ret;
> -- 
> 2.32.0