linux-kernel - Re: [PATCH] power: supply: surface-charger: replace deprecated strncpy with strscpy

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Message-ID: <5b9cf91a-d726-44d0-99e4-9440c6bd3165@gmail.com>
Date:   Sat, 21 Oct 2023 10:44:12 +0200
From:   Maximilian Luz <luzmaximilian@...il.com>
To:     Justin Stitt <justinstitt@...gle.com>,
        Sebastian Reichel <sre@...nel.org>
Cc:     linux-pm@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] power: supply: surface-charger: replace deprecated
 strncpy with strscpy

On 10/20/23 21:46, Justin Stitt wrote:
> strncpy() is deprecated for use on NUL-terminated destination strings
> [1] and as such we should prefer more robust and less ambiguous string
> interfaces.
> 
> We expect ac->name to be NUL-terminated based on its usage with format
> strings:
> 
> surface_charger.c:
> 190: ac->psy_desc.name = ac->name;
> 
> ...
> 
> power_supply_core.c:
> 174: dev_dbg(&psy->dev, "%s: Found supply : %s\n",
> 175:   psy->desc->name, epsy->desc->name);
> 
> Moreover, NUL-padding is not required as ac is already zero-allocated
> before being passed to spwr_ac_init():
> 
> surface_charger.c:
> 240: ac = devm_kzalloc(&sdev->dev, sizeof(*ac), GFP_KERNEL);
> 241: if (!ac)
> 242:   return -ENOMEM;
> 243:
> 244: spwr_ac_init(ac, sdev, p->registry, p->name);
> 
> ... this means any future NUL-byte assignments (like the ones that
> strncpy() does) are redundant.
> 
> Considering the above, a suitable replacement is `strscpy` [2] due to
> the fact that it guarantees NUL-termination on the destination buffer
> without unnecessarily NUL-padding.
> 
> Let's also opt for the more idiomatic strscpy() usage of:
> (dest, src, sizeof(dest))
> 
> 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@...r.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>

Thanks!

Reviewed-by: Maximilian Luz <luzmaximilian@...il.com>
Tested-by: Maximilian Luz <luzmaximilian@...il.com>

> ---
> Note: build-tested only.
> 
> Found with: $ rg "strncpy\("
> ---
>   drivers/power/supply/surface_charger.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/power/supply/surface_charger.c b/drivers/power/supply/surface_charger.c
> index cabdd8da12d0..7a6c62d6f883 100644
> --- a/drivers/power/supply/surface_charger.c
> +++ b/drivers/power/supply/surface_charger.c
> @@ -175,7 +175,7 @@ static void spwr_ac_init(struct spwr_ac_device *ac, struct ssam_device *sdev,
>   			 struct ssam_event_registry registry, const char *name)
>   {
>   	mutex_init(&ac->lock);
> -	strncpy(ac->name, name, ARRAY_SIZE(ac->name) - 1);
> +	strscpy(ac->name, name, sizeof(ac->name));
>   
>   	ac->sdev = sdev;
>   
> 
> ---
> base-commit: bb55d7f7f7445abcc8db50e6a65d4315e79f75c7
> change-id: 20231020-strncpy-drivers-power-supply-surface_charger-c-466920fb1f48
> 
> Best regards,
> --
> Justin Stitt <justinstitt@...gle.com>
>