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Date:   Thu, 19 Aug 2021 10:29:08 +0100
From:   Sean Young <sean@mess.org>
To:     Pavel Skripkin <paskripkin@gmail.com>
Cc:     mkrufky@linuxtv.org, mchehab@kernel.org, crope@iki.fi,
        linux-media@vger.kernel.org, linux-kernel@vger.kernel.org,
        syzbot+5ca0bf339f13c4243001@syzkaller.appspotmail.com
Subject: Re: [PATCH] media: mxl111sf: change mutex_init() location
Message-ID: <20210819092908.GA27679@gofer.mess.org>
References: <20210730213829.2909-1-paskripkin@gmail.com>
 <20210815083755.GA1827@gofer.mess.org>
 <7ee99788-d9a5-0a38-ed02-51d9b42ebc11@gmail.com>
 <80648833-5f5a-0811-a281-0dba87938d3c@gmail.com>
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On Sun, Aug 15, 2021 at 12:06:16PM +0300, Pavel Skripkin wrote:
> On 8/15/21 11:49 AM, Pavel Skripkin wrote:
> > On 8/15/21 11:37 AM, Sean Young wrote:
> > > 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.
> > > 
> > Good point. I see, that all other frontends also call
> > mxl111sf_ctrl_msg() inside ->frontend_attach() call.
> > 
> > I think, that fixing dvb-usb core is not good idea, so, I will add
> > mutex_init() call inside all frontends, which use mxl111sf_init().
> > 
> > What do you think about it?
> > 
> > 
> 
> 
> Something like this should work. Helper is just to not copy-paste code
> parts. Build tested against v5.14-rc5

How about creating a dvb_usb_device_properties probe function and
initializing the mutex init there?


Sean

> 
> 
> diff --git a/drivers/media/usb/dvb-usb-v2/mxl111sf.c
> b/drivers/media/usb/dvb-usb-v2/mxl111sf.c
> index 7865fa0a8295..db1ad3815cd5 100644
> --- a/drivers/media/usb/dvb-usb-v2/mxl111sf.c
> +++ b/drivers/media/usb/dvb-usb-v2/mxl111sf.c
> @@ -49,6 +49,13 @@ MODULE_PARM_DESC(rfswitch, "force rf switch position
> (0=auto, 1=ext, 2=int).");
> 
>  DVB_DEFINE_MOD_OPT_ADAPTER_NR(adapter_nr);
> 
> +static inline void mxl111sf_init_msg_mutex(struct dvb_usb_adapter *adap)
> +{
> +	struct mxl111sf_state *state = d_to_priv(adap_to_d(adap));
> +
> +	mutex_init(&state->msg_lock);
> +}
> +
>  int mxl111sf_ctrl_msg(struct mxl111sf_state *state,
>  		      u8 cmd, u8 *wbuf, int wlen, u8 *rbuf, int rlen)
>  {
> @@ -931,8 +938,6 @@ 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");
> @@ -963,16 +968,19 @@ static int mxl111sf_init(struct dvb_usb_device *d)
> 
>  static int mxl111sf_frontend_attach_dvbt(struct dvb_usb_adapter *adap)
>  {
> +	mxl111sf_init_msg_mutex(adap);
>  	return mxl111sf_attach_demod(adap, 0);
>  }
> 
>  static int mxl111sf_frontend_attach_atsc(struct dvb_usb_adapter *adap)
>  {
> +	mxl111sf_init_msg_mutex(adap);
>  	return mxl111sf_lgdt3305_frontend_attach(adap, 0);
>  }
> 
>  static int mxl111sf_frontend_attach_mh(struct dvb_usb_adapter *adap)
>  {
> +	mxl111sf_init_msg_mutex(adap);
>  	return mxl111sf_lg2160_frontend_attach(adap, 0);
>  }
> 
> @@ -981,6 +989,7 @@ static int mxl111sf_frontend_attach_atsc_mh(struct
> dvb_usb_adapter *adap)
>  	int ret;
>  	pr_debug("%s\n", __func__);
> 
> +	mxl111sf_init_msg_mutex(adap);
>  	ret = mxl111sf_lgdt3305_frontend_attach(adap, 0);
>  	if (ret < 0)
>  		return ret;
> @@ -1001,6 +1010,7 @@ static int mxl111sf_frontend_attach_mercury(struct
> dvb_usb_adapter *adap)
>  	int ret;
>  	pr_debug("%s\n", __func__);
> 
> +	mxl111sf_init_msg_mutex(adap);
>  	ret = mxl111sf_lgdt3305_frontend_attach(adap, 0);
>  	if (ret < 0)
>  		return ret;
> @@ -1021,6 +1031,7 @@ static int mxl111sf_frontend_attach_mercury_mh(struct
> dvb_usb_adapter *adap)
>  	int ret;
>  	pr_debug("%s\n", __func__);
> 
> +	mxl111sf_init_msg_mutex(adap);
>  	ret = mxl111sf_attach_demod(adap, 0);
>  	if (ret < 0)
>  		return ret;
> 
> 
> 
> With regards,
> Pavel Skripkin