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

[Arnd Bergmann <arnd@kernel.org>]

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.

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