linux-kernel - Re: [PATCH][V2] cpufreq: powernow-k8: add null check to policy to avoid null pointer dereference

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Message-ID: <20210105101337.fbet56iunnmkj6mn@vireshk-i7>
Date:   Tue, 5 Jan 2021 15:43:37 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Colin King <colin.king@...onical.com>
Cc:     "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Stephen Warren <swarren@...dia.com>, linux-pm@...r.kernel.org,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][V2] cpufreq: powernow-k8: add null check to policy to
 avoid null pointer dereference

Please fix the subject as well :)

On 05-01-21, 10:11, Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
> 
> Currently there is an unlikely case where cpufreq_cpu_get returns a
> null policy and this will cause a null pointer dereference later on.
> Fix this by passing the policy to transition_frequency_fidvid from the
> caller and hence eliminating the need for the cpufreq_cpu_get and
> cpufreq_cpu_put.  Thanks to Viresh Kumar for suggesting the fix.
> 
> Addresses-Coverity: ("Dereference null return")
> Fixes: b43a7ffbf33b ("cpufreq: Notify all policy->cpus in cpufreq_notify_transition()")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> ---
> 
> V2: pass the policy to transition_frequency_fidvid rather than add
>     a null pointer check on the return from a cpufreq_cpu_get call.
> ---
>  drivers/cpufreq/powernow-k8.c | 9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/cpufreq/powernow-k8.c b/drivers/cpufreq/powernow-k8.c
> index 0acc9e241cd7..b9ccb6a3dad9 100644
> --- a/drivers/cpufreq/powernow-k8.c
> +++ b/drivers/cpufreq/powernow-k8.c
> @@ -878,9 +878,9 @@ static int get_transition_latency(struct powernow_k8_data *data)
>  
>  /* Take a frequency, and issue the fid/vid transition command */
>  static int transition_frequency_fidvid(struct powernow_k8_data *data,
> -		unsigned int index)
> +		unsigned int index,
> +		struct cpufreq_policy *policy)
>  {
> -	struct cpufreq_policy *policy;
>  	u32 fid = 0;
>  	u32 vid = 0;
>  	int res;
> @@ -912,9 +912,6 @@ static int transition_frequency_fidvid(struct powernow_k8_data *data,
>  	freqs.old = find_khz_freq_from_fid(data->currfid);
>  	freqs.new = find_khz_freq_from_fid(fid);
>  
> -	policy = cpufreq_cpu_get(smp_processor_id());
> -	cpufreq_cpu_put(policy);
> -
>  	cpufreq_freq_transition_begin(policy, &freqs);
>  	res = transition_fid_vid(data, fid, vid);
>  	cpufreq_freq_transition_end(policy, &freqs, res);
> @@ -969,7 +966,7 @@ static long powernowk8_target_fn(void *arg)
>  
>  	powernow_k8_acpi_pst_values(data, newstate);
>  
> -	ret = transition_frequency_fidvid(data, newstate);
> +	ret = transition_frequency_fidvid(data, newstate, pol);
>  
>  	if (ret) {
>  		pr_err("transition frequency failed\n");
> -- 
> 2.29.2

-- 
viresh