media: mxl111sf: change mutex_init() location

stable inclusion
from stable-v4.19.222
commit 4b2d9600b31f9ba7adbc9f3c54a068615d27b390
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/IA6SIB
CVE: CVE-2021-47583

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4b2d9600b31f9ba7adbc9f3c54a068615d27b390



--------------------------------

commit 44870a9e upstream.

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_* devices call mxl111sf_ctrl_msg() in ->frontend_attach()
internally we need to initialize state->msg_lock before
frontend_attach(). To achieve it, ->probe() call added to all mxl111sf_*
devices, which will simply initiaize mutex.

Reported-and-tested-by:  <syzbot+5ca0bf339f13c4243001@syzkaller.appspotmail.com>

Fixes: 85722118 ("[media] mxl111sf: convert to new DVB USB")
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Liu Shixin <liushixin2@huawei.com>