Re: [PATCH] ACPICA: Replace strncpy() with strscpy_pad() in acpi_ut_safe_strncpy()

[Jiri Slaby <jirislaby@kernel.org>]

On 23. 03. 26, 18:31, Rafael J. Wysocki wrote:
> On Mon, Mar 23, 2026 at 6:24 PM Kees Cook <kees@kernel.org> wrote:
>>
>> Replace the deprecated[1] strncpy() with strscpy_pad() in
>> acpi_ut_safe_strncpy().
>>
>> The function is a "safe strncpy" wrapper that does
>> strncpy(dest, source, dest_size) followed by manual NUL-termination
>> at dest[dest_size - 1]. strscpy_pad() is a direct replacement: it
>> NUL-terminates, zero-pads the remainder, and the manual termination
>> is no longer needed.
>>
>> All callers pass NUL-terminated source strings (C string literals,
>> __FILE__ via ACPI_MODULE_NAME, or user-provided filenames that have
>> already been validated). The destinations are fixed-size char arrays
>> in ACPICA internal structures (allocation->module, aml_op_name,
>> acpi_gbl_db_debug_filename), all consumed as C strings.
>>
>> No behavioral change: strscpy_pad() produces identical output to
>> strncpy() + manual NUL-termination for NUL-terminated sources that
>> are shorter than dest_size. For sources longer than dest_size,
>> strncpy() wrote dest_size non-NUL bytes then the manual termination
>> overwrote the last byte with NUL; strscpy_pad() writes dest_size-1
>> bytes plus NUL: same result.
>>
>> Link: https://github.com/KSPP/linux/issues/90 [1]
>> Signed-off-by: Kees Cook <kees@kernel.org>
>> ---
>> This touches the ACPICA component shared with the upstream ACPICA
>> project (https://github.com/acpica/acpica), where the function
>> is named AcpiUtSafeStrncpy(). The upstream codebase uses its own
>> platform abstraction layer (acenv.h/acgcc.h) where I've mapped various
>> kernel APIs before like ACPI_FLEX_ARRAY and similar helpers. However,
>> acpi_ut_safe_strncpy() is an explicit function implementation rather
>> than a macro mapping, so the approach for upstreaming this change to
>> ACPICA is not clear. What's the best way to land this?
> 
> I can apply this directly, it shouldn't be a major problem for porting
> patches from the upstream.

As I reported in https://github.com/acpica/acpica/issues/1158 (but got 
no reply), this patch breaks build of acpica against 7.1-rc*:
 > ../../../../../drivers/acpi/acpica/utnonansi.c:171:9: error: implicit 
declaration of function ‘strscpy_pad’ [-Wimplicit-function-declaration]

Is strscpy_pad() supposed to be emulated in acpica?

>> (This is one of the last users of strncpy in the kernel.)
>> ---
>>   drivers/acpi/acpica/utnonansi.c | 3 +--
>>   1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/drivers/acpi/acpica/utnonansi.c b/drivers/acpi/acpica/utnonansi.c
>> index ff0802ace19b..3a7952be6545 100644
>> --- a/drivers/acpi/acpica/utnonansi.c
>> +++ b/drivers/acpi/acpica/utnonansi.c
>> @@ -168,8 +168,7 @@ void acpi_ut_safe_strncpy(char *dest, char *source, acpi_size dest_size)
>>   {
>>          /* Always terminate destination string */
>>
>> -       strncpy(dest, source, dest_size);
>> -       dest[dest_size - 1] = 0;
>> +       strscpy_pad(dest, source, dest_size);
>>   }
>>
>>   #endif
>> --
> 

thanks,
-- 
js
suse labs