[PATCH] cpufreq: refactor deprecated strncpy

[PATCH] cpufreq: refactor deprecated strncpy

[Justin Stitt]

`strncpy` is deprecated for use on NUL-terminated destination strings [1].

We should prefer more robust and less ambiguous string interfaces.

Both `policy->last_governor` and `default_governor` are expected to be
NUL-terminated which is shown by their heavy usage with other string
apis like `strcmp`.

A suitable replacement is `strscpy` [2] due to the fact that it guarantees
NUL-termination on the destination buffer.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
Link: https://github.com/KSPP/linux/issues/90
Cc: linux-hardening@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
---
Note: build-tested
---
 drivers/cpufreq/cpufreq.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 50bbc969ffe5..3eb851a03fce 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1607,7 +1607,7 @@ static void __cpufreq_offline(unsigned int cpu, struct cpufreq_policy *policy)
 	}
 
 	if (has_target())
-		strncpy(policy->last_governor, policy->governor->name,
+		strscpy(policy->last_governor, policy->governor->name,
 			CPUFREQ_NAME_LEN);
 	else
 		policy->last_policy = policy->policy;
@@ -2951,7 +2951,7 @@ static int __init cpufreq_core_init(void)
 	BUG_ON(!cpufreq_global_kobject);
 
 	if (!strlen(default_governor))
-		strncpy(default_governor, gov->name, CPUFREQ_NAME_LEN);
+		strscpy(default_governor, gov->name, CPUFREQ_NAME_LEN);
 
 	return 0;
 }

---
base-commit: 2dde18cd1d8fac735875f2e4987f11817cc0bc2c
change-id: 20230912-strncpy-drivers-cpufreq-cpufreq-c-1d800044b007

Best regards,
--
Justin Stitt <justinstitt@google.com>

Re: [PATCH] cpufreq: refactor deprecated strncpy

[Kees Cook]

On Wed, Sep 13, 2023 at 12:07:21AM +0000, Justin Stitt wrote:
> `strncpy` is deprecated for use on NUL-terminated destination strings [1].
> 
> We should prefer more robust and less ambiguous string interfaces.
> 
> Both `policy->last_governor` and `default_governor` are expected to be
> NUL-terminated which is shown by their heavy usage with other string
> apis like `strcmp`.
> 
> A suitable replacement is `strscpy` [2] due to the fact that it guarantees
> NUL-termination on the destination buffer.
> 
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
> Link: https://github.com/KSPP/linux/issues/90
> Cc: linux-hardening@vger.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@google.com>

All looks sensible to me.

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook

Re: [PATCH] cpufreq: refactor deprecated strncpy

[Viresh Kumar]

On 13-09-23, 00:07, Justin Stitt wrote:
> `strncpy` is deprecated for use on NUL-terminated destination strings [1].
> 
> We should prefer more robust and less ambiguous string interfaces.
> 
> Both `policy->last_governor` and `default_governor` are expected to be
> NUL-terminated which is shown by their heavy usage with other string
> apis like `strcmp`.
> 
> A suitable replacement is `strscpy` [2] due to the fact that it guarantees
> NUL-termination on the destination buffer.
> 
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
> Link: https://github.com/KSPP/linux/issues/90
> Cc: linux-hardening@vger.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@google.com>
> ---
> Note: build-tested
> ---
>  drivers/cpufreq/cpufreq.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 50bbc969ffe5..3eb851a03fce 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -1607,7 +1607,7 @@ static void __cpufreq_offline(unsigned int cpu, struct cpufreq_policy *policy)
>  	}
>  
>  	if (has_target())
> -		strncpy(policy->last_governor, policy->governor->name,
> +		strscpy(policy->last_governor, policy->governor->name,
>  			CPUFREQ_NAME_LEN);
>  	else
>  		policy->last_policy = policy->policy;
> @@ -2951,7 +2951,7 @@ static int __init cpufreq_core_init(void)
>  	BUG_ON(!cpufreq_global_kobject);
>  
>  	if (!strlen(default_governor))
> -		strncpy(default_governor, gov->name, CPUFREQ_NAME_LEN);
> +		strscpy(default_governor, gov->name, CPUFREQ_NAME_LEN);
>  
>  	return 0;
>  }

Acked-by: Viresh Kumar <viresh.kumar@linaro.org>

-- 
viresh

Re: [PATCH] cpufreq: refactor deprecated strncpy

[Kees Cook]

On Wed, 13 Sep 2023 00:07:21 +0000, Justin Stitt wrote:
> `strncpy` is deprecated for use on NUL-terminated destination strings [1].
> 
> We should prefer more robust and less ambiguous string interfaces.
> 
> Both `policy->last_governor` and `default_governor` are expected to be
> NUL-terminated which is shown by their heavy usage with other string
> apis like `strcmp`.
> 
> [...]

Applied to for-next/hardening, thanks!

[1/1] cpufreq: refactor deprecated strncpy
      https://git.kernel.org/kees/c/598b1b1c8f35

Take care,

-- 
Kees Cook