Add sodium_stackzero()

src/libsodium/include/sodium/utils.h

@@ -21,6 +21,9 @@ extern "C" {
 SODIUM_EXPORT
 void sodium_memzero(void * const pnt, const size_t len);
 
+SODIUM_EXPORT
+void sodium_stackzero(const size_t len);
+
 /*
  * WARNING: sodium_memcmp() must be used to verify if two secret keys
  * are equal, in constant time.

src/libsodium/sodium/utils.c

@@ -21,6 +21,23 @@
 # include <unistd.h>
 #endif
 
+#if HAVE_ALLOCA_H
+# include <alloca.h>
+#elif defined __GNUC__
+# define alloca __builtin_alloca
+#elif defined _AIX
+# define alloca __alloca
+#elif defined _MSC_VER
+# include <malloc.h>
+# define alloca _alloca
+#else
+# include <stddef.h>
+# ifdef  __cplusplus
+extern "C"
+# endif
+void *alloca (size_t);
+#endif
+
 #include "core.h"
 #include "randombytes.h"
 #include "utils.h"
@@ -103,6 +120,17 @@ sodium_memzero(void *const pnt, const size_t len)
 #endif
 }
 
+void
+sodium_stackzero(const size_t len)
+{
+#ifdef HAVE_ALLOCA
+    sodium_memzero(alloca(len), len);
+#elif __STDC_VERSION__ >= 199901L
+    unsigned char fodder[len];
+    sodium_memzero(fodder, len);
+#endif
+}
+
 #ifdef HAVE_WEAK_SYMBOLS
 __attribute__((weak)) void
 _sodium_dummy_symbol_to_prevent_memcmp_lto(const unsigned char *b1,