Add a null provider which implements no algorithms.

By loading the null provider into the default context, it is possible
to verify that it is not accidentally being used.
Reviewed-by: NMatt Caswell <matt@openssl.org>
Reviewed-by: NRichard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/11488)

crypto/provider_predefined.c

@@ -11,6 +11,7 @@
 #include "provider_local.h"
 
 OSSL_provider_init_fn ossl_default_provider_init;
+OSSL_provider_init_fn ossl_null_provider_init;
 OSSL_provider_init_fn fips_intern_provider_init;
 #ifdef STATIC_LEGACY
 OSSL_provider_init_fn ossl_legacy_provider_init;
@@ -23,6 +24,7 @@ const struct predefined_providers_st predefined_providers[] = {
 # ifdef STATIC_LEGACY
     { "legacy", ossl_legacy_provider_init, 0 },
 # endif
+    { "null", ossl_null_provider_init, 0 },
 #endif
     { NULL, NULL, 0 }
 };

doc/man7/OSSL_PROVIDER-null.pod

+=pod
+
+=head1 NAME
+
+OSSL_PROVIDER-null - OpenSSL null provider
+
+=head1 DESCRIPTION
+
+The OpenSSL null provider supplies no algorithms.
+
+It can used to guarantee that the default library context and a fallback
+provider will not be accidentally accessed.
+
+=head2 Properties
+
+The null provider defines no properties.
+
+=head1 OPERATIONS AND ALGORITHMS
+
+The OpenSSL null provider supports no operations and algorithms.
+
+=head1 SEE ALSO
+
+L<provider(7)>
+
+=head1 COPYRIGHT
+
+Copyright 2020 The OpenSSL Project Authors. All Rights Reserved.
+
+Licensed under the Apache License 2.0 (the "License").  You may not use
+this file except in compliance with the License.  You can obtain a copy
+in the file LICENSE in the source distribution or at
+L<https://www.openssl.org/source/license.html>.
+
+=cut

providers/build.info

@@ -151,3 +151,13 @@ IF[{- !$disabled{legacy} -}]
   SOURCE[$LEGACYGOAL]=legacyprov.c
   INCLUDE[$LEGACYGOAL]=../include implementations/include
 ENDIF
+
+#
+# Null provider stuff
+#
+# Because the null provider is built in, it means that libcrypto must
+# include all the object files that are needed.
+$NULLGOAL=../libcrypto
+SOURCE[$NULLGOAL]=nullprov.c
+
+

providers/nullprov.c

+/*
+ * Copyright 2020 The OpenSSL Project Authors. All Rights Reserved.
+ *
+ * Licensed under the Apache License 2.0 (the "License").  You may not use
+ * this file except in compliance with the License.  You can obtain a copy
+ * in the file LICENSE in the source distribution or at
+ * https://www.openssl.org/source/license.html
+ */
+
+#include <string.h>
+#include <stdio.h>
+#include <openssl/core.h>
+#include <openssl/core_numbers.h>
+#include <openssl/core_names.h>
+#include <openssl/params.h>
+#include "prov/implementations.h"
+
+OSSL_provider_init_fn ossl_null_provider_init;
+
+/* Functions provided by the core */
+static OSSL_core_gettable_params_fn *c_gettable_params = NULL;
+static OSSL_core_get_params_fn *c_get_params = NULL;
+
+/* Parameters we provide to the core */
+static const OSSL_ITEM null_param_types[] = {
+    { OSSL_PARAM_UTF8_PTR, OSSL_PROV_PARAM_NAME },
+    { OSSL_PARAM_UTF8_PTR, OSSL_PROV_PARAM_VERSION },
+    { OSSL_PARAM_UTF8_PTR, OSSL_PROV_PARAM_BUILDINFO },
+    { 0, NULL }
+};
+
+static const OSSL_ITEM *null_gettable_params(const OSSL_PROVIDER *prov)
+{
+    return null_param_types;
+}
+
+static int null_get_params(const OSSL_PROVIDER *prov, OSSL_PARAM params[])
+{
+    OSSL_PARAM *p;
+
+    p = OSSL_PARAM_locate(params, OSSL_PROV_PARAM_NAME);
+    if (p != NULL && !OSSL_PARAM_set_utf8_ptr(p, "OpenSSL Null Provider"))
+        return 0;
+    p = OSSL_PARAM_locate(params, OSSL_PROV_PARAM_VERSION);
+    if (p != NULL && !OSSL_PARAM_set_utf8_ptr(p, OPENSSL_VERSION_STR))
+        return 0;
+    p = OSSL_PARAM_locate(params, OSSL_PROV_PARAM_BUILDINFO);
+    if (p != NULL && !OSSL_PARAM_set_utf8_ptr(p, OPENSSL_FULL_VERSION_STR))
+        return 0;
+
+    return 1;
+}
+
+static const OSSL_ALGORITHM *null_query(OSSL_PROVIDER *prov,
+                                          int operation_id,
+                                          int *no_cache)
+{
+    *no_cache = 0;
+    return NULL;
+}
+
+/* Functions we provide to the core */
+static const OSSL_DISPATCH null_dispatch_table[] = {
+    { OSSL_FUNC_PROVIDER_GETTABLE_PARAMS, (void (*)(void))null_gettable_params },
+    { OSSL_FUNC_PROVIDER_GET_PARAMS, (void (*)(void))null_get_params },
+    { OSSL_FUNC_PROVIDER_QUERY_OPERATION, (void (*)(void))null_query },
+    { 0, NULL }
+};
+
+int ossl_null_provider_init(const OSSL_PROVIDER *provider,
+                            const OSSL_DISPATCH *in,
+                            const OSSL_DISPATCH **out,
+                            void **provctx)
+{
+    OSSL_core_get_library_context_fn *c_get_libctx = NULL;
+
+    for (; in->function_id != 0; in++) {
+        switch (in->function_id) {
+        case OSSL_FUNC_CORE_GETTABLE_PARAMS:
+            c_gettable_params = OSSL_get_core_gettable_params(in);
+            break;
+        case OSSL_FUNC_CORE_GET_PARAMS:
+            c_get_params = OSSL_get_core_get_params(in);
+            break;
+        case OSSL_FUNC_CORE_GET_LIBRARY_CONTEXT:
+            c_get_libctx = OSSL_get_core_get_library_context(in);
+            break;
+        /* Just ignore anything we don't understand */
+        default:
+            break;
+        }
+    }
+
+    if (c_get_libctx == NULL)
+        return 0;
+
+    *out = null_dispatch_table;
+
+    /*
+     * We want to make sure that all calls from this provider that requires
+     * a library context use the same context as the one used to call our
+     * functions.  We do that by passing it along as the provider context.
+     */
+    *provctx = c_get_libctx(provider);
+    return 1;
+}

test/recipes/20-test_provider.t

@@ -14,7 +14,7 @@ use OpenSSL::Test;
 
 setup("test_provider");
 
-plan tests => 7;
+plan tests => 9;
 
  SKIP: {
      skip "No default provider?", 6
@@ -45,3 +45,18 @@ plan tests => 7;
      }
 }
 
+ SKIP: {
+     skip "No null provider?", 1
+         unless ok(run(app([qw(openssl provider null)])),
+                   "try running 'openssl provider null'");
+
+     my @cmd = ('openssl', 'provider', '-vvv', 'null');
+     my @lines = ( map { (my $x = $_) =~ s|\R$||; $x }
+                   run(app([@cmd]), capture => 1) );
+
+     my $curr = scalar @lines;
+     my $cmp = "$curr == 1";
+     ok(eval $cmp,
+        "'openssl provider $_ default' line count == 1");
+}
+