Re: [PATCH] media: mxl111sf: change mutex_init() location

Sean Young
2021-08-15T08:38:03Z

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@syzkaller.appspotmail.com
> Fixes: 8572211842af ("[media] mxl111sf: convert to new DVB USB")
> Signed-off-by: Pavel Skripkin <paskripkin@gmail.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