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Subject: Re: [PATCH] media: mxl111sf: change mutex_init() location
To:     Sean Young <sean@mess.org>
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
References: <20210730213829.2909-1-paskripkin@gmail.com>
 <20210815083755.GA1827@gofer.mess.org>
From:   Pavel Skripkin <paskripkin@gmail.com>
Message-ID: <7ee99788-d9a5-0a38-ed02-51d9b42ebc11@gmail.com>
Date:   Sun, 15 Aug 2021 11:49:26 +0300
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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?


With regards,
Pavel Skripkin