Set last_comp_version correctly in new dtb and fix potential version issues in fdt_open_into

Changes in v3:
- Remove noop version sets
- Set version correctly on loaded fdt in fdt_open_into

Fixes: f1879e1a50 ("Add limited read-only support for older (V2 and V3) device tree to libfdt.")

Signed-off-by: Justin Covell <jujugoboom@gmail.com>

Message-Id: <20201229041749.2187-1-jujugoboom@gmail.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

libfdt/fdt_rw.c

@@ -428,12 +428,14 @@ int fdt_open_into(const void *fdt, void *buf, int bufsize)
 
 	if (can_assume(LATEST) || fdt_version(fdt) >= 17) {
 		struct_size = fdt_size_dt_struct(fdt);
-	} else {
+	} else if (fdt_version(fdt) == 16) {
 		struct_size = 0;
 		while (fdt_next_tag(fdt, struct_size, &struct_size) != FDT_END)
 			;
 		if (struct_size < 0)
 			return struct_size;
+	} else {
+		return -FDT_ERR_BADVERSION;
 	}
 
 	if (can_assume(LIBFDT_ORDER) ||

libfdt/fdt_sw.c

@@ -377,7 +377,7 @@ int fdt_finish(void *fdt)
 	fdt_set_totalsize(fdt, newstroffset + fdt_size_dt_strings(fdt));
 
 	/* And fix up fields that were keeping intermediate state. */
-	fdt_set_last_comp_version(fdt, FDT_FIRST_SUPPORTED_VERSION);
+	fdt_set_last_comp_version(fdt, FDT_LAST_COMPATIBLE_VERSION);
 	fdt_set_magic(fdt, FDT_MAGIC);
 
 	return 0;

libfdt/libfdt.h

@@ -14,6 +14,7 @@ extern "C" {
 #endif
 
 #define FDT_FIRST_SUPPORTED_VERSION	0x02
+#define FDT_LAST_COMPATIBLE_VERSION 0x10
 #define FDT_LAST_SUPPORTED_VERSION	0x11
 
 /* Error codes: informative error codes */