[PATCH v2] ACPICA: Replace fake flexible arrays with flexible array members

[Kees Cook <keescook@chromium.org>]

One-element arrays (and multi-element arrays being treated as
dynamically sized) are deprecated[1] and are being replaced with
flexible array members in support of the ongoing efforts to tighten the
FORTIFY_SOURCE routines on memcpy(), correctly instrument array indexing
with UBSAN_BOUNDS, and to globally enable -fstrict-flex-arrays=3.

Replace one-element array with flexible-array member in struct
acpi_resource_extended_irq. Replace 4-byte fixed-size array with 4-byte
padding in a union with a flexible-array member in struct
acpi_pci_routing_table.

This results in no differences in binary output.

Link: https://github.com/acpica/acpica/pull/813
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
v2: include stddef.h and switch to __DECLARE_FLEX_ARRAY()
v1: https://lore.kernel.org/lkml/20221118181538.never.225-kees@kernel.org/
---
 include/acpi/acrestyp.h | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/include/acpi/acrestyp.h b/include/acpi/acrestyp.h
index a7fb8ddb3dc6..250046a7c870 100644
--- a/include/acpi/acrestyp.h
+++ b/include/acpi/acrestyp.h
@@ -10,6 +10,8 @@
 #ifndef __ACRESTYP_H__
 #define __ACRESTYP_H__
 
+#include <linux/stddef.h>
+
 /*
  * Definitions for Resource Attributes
  */
@@ -332,7 +334,7 @@ struct acpi_resource_extended_irq {
 	u8 wake_capable;
 	u8 interrupt_count;
 	struct acpi_resource_source resource_source;
-	u32 interrupts[1];
+	u32 interrupts[];
 };
 
 struct acpi_resource_generic_register {
@@ -679,7 +681,10 @@ struct acpi_pci_routing_table {
 	u32 pin;
 	u64 address;		/* here for 64-bit alignment */
 	u32 source_index;
-	char source[4];		/* pad to 64 bits so sizeof() works in all cases */
+	union {
+		char pad[4];	/* pad to 64 bits so sizeof() works in all cases */
+		__DECLARE_FLEX_ARRAY(char, source);
+	};
 };
 
 #endif				/* __ACRESTYP_H__ */
-- 
2.34.1