dtc: add integer overflow checks in fdt header

Protect against integer overflows caused by malformed fdt headers.

CRs-Fixed: 749977
Change-Id: I51d87038f520bc761b163d291b0138c513c69a33
Signed-off-by: Vijay Kumar Pendoti <vpendo@codeaurora.org>
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>
diff --git a/scripts/dtc/libfdt/fdt_rw.c b/scripts/dtc/libfdt/fdt_rw.c
index 8e7ec4c..83bd47c 100644
--- a/scripts/dtc/libfdt/fdt_rw.c
+++ b/scripts/dtc/libfdt/fdt_rw.c
@@ -367,7 +367,7 @@
 static void _fdt_packblocks(const char *old, char *new,
 			    int mem_rsv_size, int struct_size)
 {
-	int mem_rsv_off, struct_off, strings_off;
+	uint32_t mem_rsv_off, struct_off, strings_off;
 
 	mem_rsv_off = FDT_ALIGN(sizeof(struct fdt_header), 8);
 	struct_off = mem_rsv_off + mem_rsv_size;