Merge pull request #7933 from tom-cosgrove-arm/add-mbedtls_zeroize_and_free

Provide and use internal function mbedtls_zeroize_and_free()

library/common.h

@@ -114,6 +114,20 @@ extern void (*mbedtls_test_hook_test_fail)(const char *test, int line, const cha
  */
 #define MBEDTLS_ALLOW_PRIVATE_ACCESS
 
+/**
+ * \brief       Securely zeroize a buffer then free it.
+ *
+ *              Similar to making consecutive calls to
+ *              \c mbedtls_platform_zeroize() and \c mbedtls_free(), but has
+ *              code size savings, and potential for optimisation in the future.
+ *
+ *              Guaranteed to be a no-op if \p buf is \c NULL and \p len is 0.
+ *
+ * \param buf   Buffer to be zeroized then freed.
+ * \param len   Length of the buffer in bytes
+ */
+void mbedtls_zeroize_and_free(void *buf, size_t len);
+
 /** Return an offset into a buffer.
  *
  * This is just the addition of an offset to a pointer, except that this