linux-kernel - Re: [PATCH] thermal: Fix a NULL pointer dereference

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Date:   Fri, 3 Sep 2021 18:07:56 -0700
From:   David Collins <quic_collinsd@...cinc.com>
To:     Subbaraman Narayanamurthy <quic_subbaram@...cinc.com>,
        Zhang Rui <rui.zhang@...el.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        "Amit Kucheria" <amitk@...nel.org>
CC:     <linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <stable@...r.kernel.org>, David Collins <quic_collinsd@...cinc.com>
Subject: Re: [PATCH] thermal: Fix a NULL pointer dereference

On 9/3/21 5:34 PM, Subbaraman Narayanamurthy wrote:
> of_parse_thermal_zones() parses the thermal-zones node and registers a
> thermal_zone device for each subnode. However, if a thermal zone is
> consuming a thermal sensor and that thermal sensor device hasn't probed
> yet, an attempt to set trip_point_*_temp for that thermal zone device
> can cause a NULL pointer dereference. Fix it.
> 
>   console:/sys/class/thermal/thermal_zone87 # echo 120000 > trip_point_0_temp
>   ...
>   Unable to handle kernel NULL pointer dereference at virtual address 0000000000000020
>   ...
>   Call trace:
>    of_thermal_set_trip_temp+0x40/0xc4
>    trip_point_temp_store+0xc0/0x1dc
>    dev_attr_store+0x38/0x88
>    sysfs_kf_write+0x64/0xc0
>    kernfs_fop_write_iter+0x108/0x1d0
>    vfs_write+0x2f4/0x368
>    ksys_write+0x7c/0xec
>    __arm64_sys_write+0x20/0x30
>    el0_svc_common.llvm.7279915941325364641+0xbc/0x1bc
>    do_el0_svc+0x28/0xa0
>    el0_svc+0x14/0x24
>    el0_sync_handler+0x88/0xec
>    el0_sync+0x1c0/0x200
> 
> Cc: stable@...r.kernel.org
> Suggested-by: David Collins <quic_collinsd@...cinc.com>
> Signed-off-by: Subbaraman Narayanamurthy <quic_subbaram@...cinc.com>
> ---
>   drivers/thermal/thermal_of.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/thermal/thermal_of.c b/drivers/thermal/thermal_of.c
> index 6379f26..ba53252 100644
> --- a/drivers/thermal/thermal_of.c
> +++ b/drivers/thermal/thermal_of.c
> @@ -301,7 +301,7 @@ static int of_thermal_set_trip_temp(struct thermal_zone_device *tz, int trip,
>   	if (trip >= data->ntrips || trip < 0)
>   		return -EDOM;
>   
> -	if (data->ops->set_trip_temp) {
> +	if (data->ops && data->ops->set_trip_temp) {
>   		int ret;
>   
>   		ret = data->ops->set_trip_temp(data->sensor_data, trip, temp);
> 

It looks like the same kind of data->ops null pointer dereference issue is 
present in three other functions within this file: of_thermal_get_temp(), 
of_thermal_set_emul_temp(), and of_thermal_get_trend().  Should those be 
fixed along with of_thermal_set_trip_temp() in a single patch?

Thanks,
David