Fix nc_email to check ASN1 strings with NULL byte in the middle

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/16524)

crypto/x509/v3_ncons.c

@@ -714,6 +714,9 @@ static int nc_email(ASN1_IA5STRING *eml, ASN1_IA5STRING *base)
         if (baseat != baseptr) {
             if ((baseat - baseptr) != (emlat - emlptr))
                 return X509_V_ERR_PERMITTED_VIOLATION;
+            if (memchr(baseptr, 0, baseat - baseptr) ||
+                memchr(emlptr, 0, emlat - emlptr))
+                return X509_V_ERR_UNSUPPORTED_NAME_SYNTAX;
             /* Case sensitive match of local part */
             if (strncmp(baseptr, emlptr, emlat - emlptr))
                 return X509_V_ERR_PERMITTED_VIOLATION;