linux-hardening - Re: [PATCH v3] x86/platform/uv: refactor deprecated strcpy and strncpy

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Date:   Wed, 6 Sep 2023 13:42:48 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     Justin Stitt <justinstitt@...gle.com>,
        Steve Wahl <steve.wahl@....com>,
        Mike Travis <mike.travis@....com>,
        Dimitri Sivanich <dimitri.sivanich@....com>,
        Russ Anderson <russ.anderson@....com>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>
Cc:     platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH v3] x86/platform/uv: refactor deprecated strcpy and
 strncpy

Hi,

On 9/5/23 23:54, Justin Stitt wrote:
> Both `strncpy` and `strcpy` are deprecated for use on NUL-terminated
> destination strings [1].
> 
> We can see that `arg` and `uv_nmi_action` are expected to be
> NUL-terminated strings due to their use within `strcmp()` and format
> strings respectively.
> 
> With this in mind, a suitable replacement is `strscpy` [2] due to the
> fact that it guarantees NUL-termination on its destination buffer
> argument which is _not_ the case for `strncpy` or `strcpy`!
> 
> In this case, we can drop both the forced NUL-termination and the `... -1` from:
> |       strncpy(arg, val, ACTION_LEN - 1);
> as `strscpy` implicitly has this behavior.
> 
> Link: 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>
> ---
> Changes in v3:
> - Use sizeof instead of strlen (thanks Andy and Dimitri)
> - Drop unrelated changes regarding strnchrnul (thanks Hans)
> - Link to v2: https://lore.kernel.org/r/20230824-strncpy-arch-x86-platform-uv-uv_nmi-v2-1-e16d9a3ec570@google.com

Thanks, patch looks good to me:

Reviewed-by: Hans de Goede <hdegoede@...hat.com>

Regards,

Hans


> 
> Changes in v2:
> - use `sizeof` on destination string instead of `strlen` (thanks Andy, Kees and Dimitri)
> - refactor code to remove potential new-line chars (thanks Yang Yang and Andy)
> - Link to v1: https://lore.kernel.org/r/20230822-strncpy-arch-x86-platform-uv-uv_nmi-v1-1-931f2943de0d@google.com
> ---
> Note: build-tested only
> ---
>  arch/x86/platform/uv/uv_nmi.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/platform/uv/uv_nmi.c b/arch/x86/platform/uv/uv_nmi.c
> index a60af0230e27..dd30fb2baf6c 100644
> --- a/arch/x86/platform/uv/uv_nmi.c
> +++ b/arch/x86/platform/uv/uv_nmi.c
> @@ -205,8 +205,7 @@ static int param_set_action(const char *val, const struct kernel_param *kp)
>  	char arg[ACTION_LEN], *p;
>  
>  	/* (remove possible '\n') */
> -	strncpy(arg, val, ACTION_LEN - 1);
> -	arg[ACTION_LEN - 1] = '\0';
> +	strscpy(arg, val, sizeof(arg));
>  	p = strchr(arg, '\n');
>  	if (p)
>  		*p = '\0';
> @@ -216,7 +215,7 @@ static int param_set_action(const char *val, const struct kernel_param *kp)
>  			break;
>  
>  	if (i < n) {
> -		strcpy(uv_nmi_action, arg);
> +		strscpy(uv_nmi_action, arg, sizeof(uv_nmi_action));
>  		pr_info("UV: New NMI action:%s\n", uv_nmi_action);
>  		return 0;
>  	}
> @@ -959,7 +958,7 @@ static int uv_handle_nmi(unsigned int reason, struct pt_regs *regs)
>  
>  		/* Unexpected return, revert action to "dump" */
>  		if (master)
> -			strncpy(uv_nmi_action, "dump", strlen(uv_nmi_action));
> +			strscpy(uv_nmi_action, "dump", sizeof(uv_nmi_action));
>  	}
>  
>  	/* Pause as all CPU's enter the NMI handler */
> 
> ---
> base-commit: 2dde18cd1d8fac735875f2e4987f11817cc0bc2c
> change-id: 20230822-strncpy-arch-x86-platform-uv-uv_nmi-474e5295c2c1
> 
> Best regards,
> --
> Justin Stitt <justinstitt@...gle.com>
>