linux-kernel - Re: [PATCH 06/11] acpi: avoid warning for truncated string copy

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Date: Thu, 28 Mar 2024 23:20:47 +0000
From: Justin Stitt <justinstitt@...gle.com>
To: Arnd Bergmann <arnd@...nel.org>
Cc: linux-kernel@...r.kernel.org, Robert Moore <robert.moore@...el.com>, 
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>, Alexey Starikovskiy <astarikovskiy@...e.de>, 
	Lin Ming <ming.m.lin@...el.com>, Len Brown <len.brown@...el.com>, Arnd Bergmann <arnd@...db.de>, 
	Len Brown <lenb@...nel.org>, linux-acpi@...r.kernel.org, acpica-devel@...ts.linux.dev
Subject: Re: [PATCH 06/11] acpi: avoid warning for truncated string copy

Hi,

On Thu, Mar 28, 2024 at 03:04:50PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> gcc -Wstringop-truncation warns about copying a string that results in a
> missing nul termination:
> 
> drivers/acpi/acpica/tbfind.c: In function 'acpi_tb_find_table':
> drivers/acpi/acpica/tbfind.c:60:9: error: 'strncpy' specified bound 6 equals destination size [-Werror=stringop-truncation]
>    60 |         strncpy(header.oem_id, oem_id, ACPI_OEM_ID_SIZE);
>       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/acpi/acpica/tbfind.c:61:9: error: 'strncpy' specified bound 8 equals destination size [-Werror=stringop-truncation]
>    61 |         strncpy(header.oem_table_id, oem_table_id, ACPI_OEM_TABLE_ID_SIZE);
>       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> This one is intentional, so rewrite the code in a way that avoids the
> warning. Since there is already an extra strlen() and an overflow check,
> the actual size to be copied is already known here.
>
I also tried cleaning these up but Kees informed me that this subsystem
is maintained elsewhere:

https://lore.kernel.org/all/202308241612.DFE4119@keescook/

I am not sure if you can get changes through by the traditional means.

> 
> Fixes: 47c08729bf1c ("ACPICA: Fix for LoadTable operator, input strings")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/acpi/acpica/tbfind.c | 19 +++++++++----------
>  1 file changed, 9 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/acpi/acpica/tbfind.c b/drivers/acpi/acpica/tbfind.c
> index 1c1b2e284bd9..472ce2a6624b 100644
> --- a/drivers/acpi/acpica/tbfind.c
> +++ b/drivers/acpi/acpica/tbfind.c
> @@ -36,7 +36,7 @@ acpi_tb_find_table(char *signature,
>  {
>  	acpi_status status = AE_OK;
>  	struct acpi_table_header header;
> -	u32 i;
> +	u32 len, i;
>  
>  	ACPI_FUNCTION_TRACE(tb_find_table);
>  
> @@ -46,19 +46,18 @@ acpi_tb_find_table(char *signature,
>  		return_ACPI_STATUS(AE_BAD_SIGNATURE);
>  	}
>  
> -	/* Don't allow the OEM strings to be too long */
> -
> -	if ((strlen(oem_id) > ACPI_OEM_ID_SIZE) ||
> -	    (strlen(oem_table_id) > ACPI_OEM_TABLE_ID_SIZE)) {
> -		return_ACPI_STATUS(AE_AML_STRING_LIMIT);
> -	}
> -
>  	/* Normalize the input strings */
>  
>  	memset(&header, 0, sizeof(struct acpi_table_header));
>  	ACPI_COPY_NAMESEG(header.signature, signature);
> -	strncpy(header.oem_id, oem_id, ACPI_OEM_ID_SIZE);
> -	strncpy(header.oem_table_id, oem_table_id, ACPI_OEM_TABLE_ID_SIZE);
> +	len = strlen(oem_id);
> +	if (len > ACPI_OEM_ID_SIZE)
> +		return_ACPI_STATUS(AE_AML_STRING_LIMIT);
> +	memcpy(header.oem_id, oem_id, len);
> +	len = strlen(oem_table_id);
> +	if (len > ACPI_OEM_TABLE_ID_SIZE)
> +		return_ACPI_STATUS(AE_AML_STRING_LIMIT);
> +	memcpy(header.oem_table_id, oem_table_id, len);
>  
>  	/* Search for the table */
>  
> -- 
> 2.39.2
> 
Thanks
Justin