Avoid integer overflows during memory allocation.

It is possible to overflow integers during memory allocation with
insanely large "key bytes" specified in a LUKS header.

Although it could be argued to properly validate LUKS headers while
parsing them, it's still a good idea to fix any form of possible
overflow attacks against cryptsetup in these allocation functions.

lib/utils_crypt.c

@@ -22,6 +22,7 @@
 
 #include <stdlib.h>
 #include <stddef.h>
+#include <stdint.h>
 #include <stdio.h>
 #include <string.h>
 #include <errno.h>
@@ -98,7 +99,7 @@ void *crypt_safe_alloc(size_t size)
 {
 	struct safe_allocation *alloc;
 
-	if (!size)
+	if (!size || size > (SIZE_MAX - offsetof(struct safe_allocation, data)))
 		return NULL;
 
 	alloc = malloc(size + offsetof(struct safe_allocation, data));