linux-kernel - Re: [PATCH] cppc_cpufreq: Fix possible null pointer dereference

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Date: Fri, 5 Apr 2024 16:08:55 +0530
From: Mukesh Ojha <quic_mojha@...cinc.com>
To: Aleksandr Mishin <amishin@...rgos.ru>,
        Ionela Voinescu
	<ionela.voinescu@....com>
CC: "Rafael J. Wysocki" <rafael@...nel.org>,
        Viresh Kumar
	<viresh.kumar@...aro.org>, <linux-pm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <lvc-project@...uxtesting.org>
Subject: Re: [PATCH] cppc_cpufreq: Fix possible null pointer dereference



On 4/5/2024 3:10 PM, Aleksandr Mishin wrote:
> cppc_cpufreq_get_rate() and hisi_cppc_cpufreq_get_rate() can be called from
> different places with various parameters. So cpufreq_cpu_get() can return
> null as 'policy' in some circumstances.
> Fix this bug by adding null return check.
> 
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
> 
> Fixes: a28b2bfc099c ("cppc_cpufreq: replace per-cpu data array with a list")
> Signed-off-by: Aleksandr Mishin <amishin@...rgos.ru>
> ---
>   drivers/cpufreq/cppc_cpufreq.c | 6 ++++++
>   1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
> index 64420d9cfd1e..5f7e04e8497b 100644
> --- a/drivers/cpufreq/cppc_cpufreq.c
> +++ b/drivers/cpufreq/cppc_cpufreq.c
> @@ -741,6 +741,9 @@ static unsigned int cppc_cpufreq_get_rate(unsigned int cpu)
>   {
>   	struct cppc_perf_fb_ctrs fb_ctrs_t0 = {0}, fb_ctrs_t1 = {0};
>   	struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
> +	if (!policy)
> +		return -ENODEV;
> +

You should be doing this after all variable declaration, somewhere

..
..
struct cppc_cpudata *cpu_data;
u64 delivered_perf;
int ret;

if (!policy)
	return -ENODEV;

cpu_data = policy->driver_data;
.
.

>   	struct cppc_cpudata *cpu_data = policy->driver_data;
>   	u64 delivered_perf;
>   	int ret;
> @@ -822,6 +825,9 @@ static struct cpufreq_driver cppc_cpufreq_driver = {
>   static unsigned int hisi_cppc_cpufreq_get_rate(unsigned int cpu)
>   {
>   	struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);

same here.

> +	if (!policy)
> +		return -ENODEV;
> +
>   	struct cppc_cpudata *cpu_data = policy->driver_data;
>   	u64 desired_perf;
>   	int ret;

-Mukesh