linux-kernel - Re: [PATCH] drivers: thermal: Add NULL pointer check before using cooling device stats

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Date:   Fri, 4 Dec 2020 20:21:01 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Manaf Meethalavalappu Pallikunhi <manafm@...eaurora.org>,
        Zhang Rui <rui.zhang@...el.com>,
        Eduardo Valentin <edubezval@...il.com>,
        Amit Kucheria <amit.kucheria@...durent.com>,
        Ram Chandrasekar <rkumbako@...eaurora.org>
Cc:     linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drivers: thermal: Add NULL pointer check before using
 cooling device stats

On 04/12/2020 20:09, Manaf Meethalavalappu Pallikunhi wrote:
> There is a possible chance that some cooling device stats buffer
> allocation fails due to very high cooling device max state value.
> Later cooling device update or cooling stats sysfs will try to
> access stats data for the same cooling device. It will lead to
> NULL pointer dereference issue.
> 
> Add a NULL pointer check before accessing thermal cooling device
> stats data. It fixes the following bug

Why not create the 'stats' dir if the setup fails ?

> [ 26.812833] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000004
> [ 27.122960] Call trace:
> [ 27.122963] do_raw_spin_lock+0x18/0xe8
> [ 27.122966] _raw_spin_lock+0x24/0x30
> [ 27.128157] thermal_cooling_device_stats_update+0x24/0x98
> [ 27.128162] cur_state_store+0x88/0xb8
> [ 27.128166] dev_attr_store+0x40/0x58
> [ 27.128169] sysfs_kf_write+0x50/0x68
> [ 27.133358] kernfs_fop_write+0x12c/0x1c8
> [ 27.133362] __vfs_write+0x54/0x160
> [ 27.152297] vfs_write+0xcc/0x188
> [ 27.157132] ksys_write+0x78/0x108
> [ 27.162050] ksys_write+0xf8/0x108
> [ 27.166968] __arm_smccc_hvc+0x158/0x4b0
> [ 27.166973] __arm_smccc_hvc+0x9c/0x4b0
> [ 27.186005] el0_svc+0x8/0xc
> 
> Signed-off-by: Manaf Meethalavalappu Pallikunhi <manafm@...eaurora.org>
> ---
>  drivers/thermal/thermal_sysfs.c | 18 +++++++++++++++++-
>  1 file changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/thermal/thermal_sysfs.c b/drivers/thermal/thermal_sysfs.c
> index 473449b..a5e4855 100644
> --- a/drivers/thermal/thermal_sysfs.c
> +++ b/drivers/thermal/thermal_sysfs.c
> @@ -827,6 +827,9 @@ void thermal_cooling_device_stats_update(struct thermal_cooling_device *cdev,
>  {
>  	struct cooling_dev_stats *stats = cdev->stats;
>  
> +	if (!stats)
> +		return;
> +
>  	spin_lock(&stats->lock);
>  
>  	if (stats->state == new_state)
> @@ -848,6 +851,9 @@ static ssize_t total_trans_show(struct device *dev,
>  	struct cooling_dev_stats *stats = cdev->stats;
>  	int ret;
>  
> +	if (!stats)
> +		return -ENODEV;
> +
>  	spin_lock(&stats->lock);
>  	ret = sprintf(buf, "%u\n", stats->total_trans);
>  	spin_unlock(&stats->lock);
> @@ -864,6 +870,9 @@ time_in_state_ms_show(struct device *dev, struct device_attribute *attr,
>  	ssize_t len = 0;
>  	int i;
>  
> +	if (!stats)
> +		return -ENODEV;
> +
>  	spin_lock(&stats->lock);
>  	update_time_in_state(stats);
>  
> @@ -882,8 +891,12 @@ reset_store(struct device *dev, struct device_attribute *attr, const char *buf,
>  {
>  	struct thermal_cooling_device *cdev = to_cooling_device(dev);
>  	struct cooling_dev_stats *stats = cdev->stats;
> -	int i, states = stats->max_states;
> +	int i, states;
> +
> +	if (!stats)
> +		return -ENODEV;
>  
> +	states = stats->max_states;
>  	spin_lock(&stats->lock);
>  
>  	stats->total_trans = 0;
> @@ -907,6 +920,9 @@ static ssize_t trans_table_show(struct device *dev,
>  	ssize_t len = 0;
>  	int i, j;
>  
> +	if (!stats)
> +		return -ENODEV;
> +
>  	len += snprintf(buf + len, PAGE_SIZE - len, " From  :    To\n");
>  	len += snprintf(buf + len, PAGE_SIZE - len, "       : ");
>  	for (i = 0; i < stats->max_states; i++) {
> 


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