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

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Message-ID: <80648833-5f5a-0811-a281-0dba87938d3c@gmail.com>
Date:   Sun, 15 Aug 2021 12:06:16 +0300
From:   Pavel Skripkin <paskripkin@...il.com>
To:     Sean Young <sean@...s.org>
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 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


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