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

Justin Stitt
2024-03-28T23:20:51Z

Hi,

On Thu, Mar 28, 2024 at 03:04:50PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.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@arndb.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