linux-kernel - Re: [PATCH v2] thermal: Fix a NULL pointer dereference

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Date:   Fri, 17 Sep 2021 11:31:00 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Subbaraman Narayanamurthy <quic_subbaram@...cinc.com>,
        Zhang Rui <rui.zhang@...el.com>,
        Amit Kucheria <amitk@...nel.org>
Cc:     linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        David Collins <quic_collinsd@...cinc.com>,
        Manaf Meethalavalappu Pallikunhi <manafm@...eaurora.org>,
        Ram Chandrasekar <rkumbako@...eaurora.org>,
        stable@...r.kernel.org
Subject: Re: [PATCH v2] thermal: Fix a NULL pointer dereference

On 07/09/2021 21:01, 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
> 
> While at it, fix the possible NULL pointer dereference in other
> functions as well: of_thermal_get_temp(), of_thermal_set_emul_temp(),
> of_thermal_get_trend().
> 
> Cc: stable@...r.kernel.org
> Suggested-by: David Collins <quic_collinsd@...cinc.com>
> Signed-off-by: Subbaraman Narayanamurthy <quic_subbaram@...cinc.com>
> ---
> Changes for v2:
> - Added checks in of_thermal_get_temp(), of_thermal_set_emul_temp(), of_thermal_get_trend().
> 
>  drivers/thermal/thermal_of.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/thermal/thermal_of.c b/drivers/thermal/thermal_of.c
> index 6379f26..9233f7e 100644
> --- a/drivers/thermal/thermal_of.c
> +++ b/drivers/thermal/thermal_of.c
> @@ -89,7 +89,7 @@ static int of_thermal_get_temp(struct thermal_zone_device *tz,
>  {
>  	struct __thermal_zone *data = tz->devdata;
>  
> -	if (!data->ops->get_temp)
> +	if (!data->ops || !data->ops->get_temp)

comment (1)

AFAICT, if data->ops != NULL then data->ops->get_temp is also != NULL
because of the code allocating/freeing the ops structure.

The tests can be replaced by (!data->ops), no ?

>  		return -EINVAL;
>  
>  	return data->ops->get_temp(data->sensor_data, temp);
> @@ -186,6 +186,9 @@ static int of_thermal_set_emul_temp(struct thermal_zone_device *tz,
>  {
>  	struct __thermal_zone *data = tz->devdata;
>  
> +	if (!data->ops || !data->ops->set_emul_temp)
> +		return -EINVAL;
> +

comment (2)

The test looks pointless here (I mean both of them).

If of_thermal_set_emul_temp() is called it is because the callback was
set in thermal_zone_of_add_sensor().

This one does:

	tz->ops = ops;

and
	if (ops->set_emul_temp)
                tzd->ops->set_emul_temp = of_thermal_set_emul_temp;

If I'm not wrong if we are called, then data->ops &&
data->ops->set_emul_temp is always true, right ?


>  	return data->ops->set_emul_temp(data->sensor_data, temp);
>  }
>  
> @@ -194,7 +197,7 @@ static int of_thermal_get_trend(struct thermal_zone_device *tz, int trip,
>  {
>  	struct __thermal_zone *data = tz->devdata;
>  
> -	if (!data->ops->get_trend)
> +	if (!data->ops || !data->ops->get_trend)
>  		return -EINVAL;

Same comment as (1)

>  	return data->ops->get_trend(data->sensor_data, trip, trend);
> @@ -301,7 +304,7 @@ 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) {

Same comment as (2)

>  		int ret;
>  
>  		ret = data->ops->set_trip_temp(data->sensor_data, trip, temp);
> 


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