Merge pull request #4934 from jboeuf/ssl_credentials_override_default_roots

Ssl credentials override default roots

include/grpc/grpc_security.h

@@ -147,6 +147,29 @@ GRPC_API grpc_channel_credentials *grpc_google_default_credentials_create(void);
 #define GRPC_DEFAULT_SSL_ROOTS_FILE_PATH_ENV_VAR \
   "GRPC_DEFAULT_SSL_ROOTS_FILE_PATH"
 
+/* Results for the SSL roots override callback. */
+typedef enum {
+  GRPC_SSL_ROOTS_OVERRIDE_OK,
+  GRPC_SSL_ROOTS_OVERRIDE_FAIL_PERMANENTLY, /* Do not try fallback options. */
+  GRPC_SSL_ROOTS_OVERRIDE_FAIL
+} grpc_ssl_roots_override_result;
+
+/* Callback for getting the SSL roots override from the application.
+   In case of success, *pem_roots_certs must be set to a NULL terminated string
+   containing the list of PEM encoded root certificates. The ownership is passed
+   to the core and freed (laster by the core) with gpr_free.
+   If this function fails and GRPC_DEFAULT_SSL_ROOTS_FILE_PATH environment is
+   set to a valid path, it will override the roots specified this func */
+typedef grpc_ssl_roots_override_result (*grpc_ssl_roots_override_callback)(
+    char **pem_root_certs);
+
+/* Setup a callback to override the default TLS/SSL roots.
+   This function is not thread-safe and must be called at initialization time
+   before any ssl credentials are created to have the desired side effect.
+   If GRPC_DEFAULT_SSL_ROOTS_FILE_PATH environment is set to a valid path, the
+   callback will not be called. */
+void grpc_set_ssl_roots_override_callback(grpc_ssl_roots_override_callback cb);
+
 /* Object that holds a private key / certificate chain pair in PEM format. */
 typedef struct {
   /* private_key is the NULL-terminated string containing the PEM encoding of
@@ -163,8 +186,9 @@ typedef struct {
      of the server root certificates. If this parameter is NULL, the
      implementation will first try to dereference the file pointed by the
      GRPC_DEFAULT_SSL_ROOTS_FILE_PATH environment variable, and if that fails,
-     get the roots from a well-known place on disk (in the grpc install
-     directory).
+     try to get the roots set by grpc_override_ssl_default_roots. Eventually,
+     if all these fail, it will try to get the roots from a well-known place on
+     disk (in the grpc install directory).
    - pem_key_cert_pair is a pointer on the object containing client's private
      key and certificate chain. This parameter can be NULL if the client does
      not have such a key/cert pair. */

src/core/security/security_connector.c

@@ -61,6 +61,14 @@ static const char *installed_roots_path =
     INSTALL_PREFIX "/share/grpc/roots.pem";
 #endif
 
+/* -- Overridden default roots. -- */
+
+static grpc_ssl_roots_override_callback ssl_roots_override_cb = NULL;
+
+void grpc_set_ssl_roots_override_callback(grpc_ssl_roots_override_callback cb) {
+  ssl_roots_override_cb = cb;
+}
+
 /* -- Cipher suites. -- */
 
 /* Defines the cipher suites that we accept by default. All these cipher suites
@@ -595,23 +603,44 @@ static grpc_security_connector_vtable ssl_channel_vtable = {
 static grpc_security_connector_vtable ssl_server_vtable = {
     ssl_server_destroy, ssl_server_do_handshake, ssl_server_check_peer};
 
-static gpr_slice default_pem_root_certs;
+static gpr_slice compute_default_pem_root_certs_once(void) {
+  gpr_slice result = gpr_empty_slice();
 
-static void init_default_pem_root_certs(void) {
   /* First try to load the roots from the environment. */
   char *default_root_certs_path =
       gpr_getenv(GRPC_DEFAULT_SSL_ROOTS_FILE_PATH_ENV_VAR);
-  if (default_root_certs_path == NULL) {
-    default_pem_root_certs = gpr_empty_slice();
-  } else {
-    default_pem_root_certs = gpr_load_file(default_root_certs_path, 0, NULL);
+  if (default_root_certs_path != NULL) {
+    result = gpr_load_file(default_root_certs_path, 0, NULL);
     gpr_free(default_root_certs_path);
   }
 
+  /* Try overridden roots if needed. */
+  grpc_ssl_roots_override_result ovrd_res = GRPC_SSL_ROOTS_OVERRIDE_FAIL;
+  if (GPR_SLICE_IS_EMPTY(result) && ssl_roots_override_cb != NULL) {
+    char *pem_root_certs = NULL;
+    ovrd_res = ssl_roots_override_cb(&pem_root_certs);
+    if (ovrd_res == GRPC_SSL_ROOTS_OVERRIDE_OK) {
+      GPR_ASSERT(pem_root_certs != NULL);
+      result = gpr_slice_new(pem_root_certs, strlen(pem_root_certs), gpr_free);
+    }
+  }
+
   /* Fall back to installed certs if needed. */
-  if (GPR_SLICE_IS_EMPTY(default_pem_root_certs)) {
-    default_pem_root_certs = gpr_load_file(installed_roots_path, 0, NULL);
+  if (GPR_SLICE_IS_EMPTY(result) &&
+      ovrd_res != GRPC_SSL_ROOTS_OVERRIDE_FAIL_PERMANENTLY) {
+    result = gpr_load_file(installed_roots_path, 0, NULL);
   }
+  return result;
+}
+
+static gpr_slice default_pem_root_certs;
+
+static void init_default_pem_root_certs(void) {
+  default_pem_root_certs = compute_default_pem_root_certs_once();
+}
+
+gpr_slice grpc_get_default_ssl_roots_for_testing(void) {
+  return compute_default_pem_root_certs_once();
 }
 
 size_t grpc_get_default_ssl_roots(const unsigned char **pem_root_certs) {

src/core/security/security_connector.h

@@ -209,6 +209,9 @@ grpc_security_status grpc_ssl_channel_security_connector_create(
 /* Gets the default ssl roots. */
 size_t grpc_get_default_ssl_roots(const unsigned char **pem_root_certs);
 
+/* Exposed for TESTING ONLY!. */
+gpr_slice grpc_get_default_ssl_roots_for_testing(void);
+
 /* Config for ssl servers. */
 typedef struct {
   unsigned char **pem_private_keys;

test/core/security/security_connector_test.c

@@ -1,6 +1,6 @@
 /*
  *
- * Copyright 2015, Google Inc.
+ * Copyright 2015-2016, Google Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -36,6 +36,9 @@
 
 #include "src/core/security/security_connector.h"
 #include "src/core/security/security_context.h"
+#include "src/core/support/env.h"
+#include "src/core/support/file.h"
+#include "src/core/support/string.h"
 #include "src/core/tsi/ssl_transport_security.h"
 #include "src/core/tsi/transport_security.h"
 #include "test/core/util/test_config.h"
@@ -44,6 +47,7 @@
 
 #include <grpc/support/alloc.h>
 #include <grpc/support/log.h>
+#include <grpc/support/string_util.h>
 #include <grpc/support/useful.h>
 
 static int check_transport_security_type(const grpc_auth_context *ctx) {
@@ -297,7 +301,66 @@ static void test_cn_and_multiple_sans_and_others_ssl_peer_to_auth_context(
   GRPC_AUTH_CONTEXT_UNREF(ctx, "test");
 }
 
-/* TODO(jboeuf): Unit-test tsi_shallow_peer_from_auth_context. */
+static const char *roots_for_override_api = "roots for override api";
+
+static grpc_ssl_roots_override_result override_roots_success(
+    char **pem_root_certs) {
+  *pem_root_certs = gpr_strdup(roots_for_override_api);
+  return GRPC_SSL_ROOTS_OVERRIDE_OK;
+}
+
+static grpc_ssl_roots_override_result override_roots_permanent_failure(
+    char **pem_root_certs) {
+  return GRPC_SSL_ROOTS_OVERRIDE_FAIL_PERMANENTLY;
+}
+
+static void test_default_ssl_roots(void) {
+  const char *roots_for_env_var = "roots for env var";
+
+  char *roots_env_var_file_path;
+  FILE *roots_env_var_file =
+      gpr_tmpfile("test_roots_for_env_var", &roots_env_var_file_path);
+  fwrite(roots_for_env_var, 1, strlen(roots_for_env_var), roots_env_var_file);
+  fclose(roots_env_var_file);
+
+  /* First let's get the root through the override: set the env to an invalid
+     value. */
+  gpr_setenv(GRPC_DEFAULT_SSL_ROOTS_FILE_PATH_ENV_VAR, "");
+  grpc_set_ssl_roots_override_callback(override_roots_success);
+  gpr_slice roots = grpc_get_default_ssl_roots_for_testing();
+  char *roots_contents = gpr_dump_slice(roots, GPR_DUMP_ASCII);
+  gpr_slice_unref(roots);
+  GPR_ASSERT(strcmp(roots_contents, roots_for_override_api) == 0);
+  gpr_free(roots_contents);
+
+  /* Now let's set the env var: We should get the contents pointed value
+     instead. */
+  gpr_setenv(GRPC_DEFAULT_SSL_ROOTS_FILE_PATH_ENV_VAR, roots_env_var_file_path);
+  roots = grpc_get_default_ssl_roots_for_testing();
+  roots_contents = gpr_dump_slice(roots, GPR_DUMP_ASCII);
+  gpr_slice_unref(roots);
+  GPR_ASSERT(strcmp(roots_contents, roots_for_env_var) == 0);
+  gpr_free(roots_contents);
+
+  /* Now reset the env var. We should fall back to the value overridden using
+     the api. */
+  gpr_setenv(GRPC_DEFAULT_SSL_ROOTS_FILE_PATH_ENV_VAR, "");
+  roots = grpc_get_default_ssl_roots_for_testing();
+  roots_contents = gpr_dump_slice(roots, GPR_DUMP_ASCII);
+  gpr_slice_unref(roots);
+  GPR_ASSERT(strcmp(roots_contents, roots_for_override_api) == 0);
+  gpr_free(roots_contents);
+
+  /* Now setup a permanent failure for the overridden roots and we should get
+     an empty slice. */
+  grpc_set_ssl_roots_override_callback(override_roots_permanent_failure);
+  roots = grpc_get_default_ssl_roots_for_testing();
+  GPR_ASSERT(GPR_SLICE_IS_EMPTY(roots));
+
+  /* Cleanup. */
+  remove(roots_env_var_file_path);
+  gpr_free(roots_env_var_file_path);
+}
 
 int main(int argc, char **argv) {
   grpc_test_init(argc, argv);
@@ -308,6 +371,7 @@ int main(int argc, char **argv) {
   test_cn_and_one_san_ssl_peer_to_auth_context();
   test_cn_and_multiple_sans_ssl_peer_to_auth_context();
   test_cn_and_multiple_sans_and_others_ssl_peer_to_auth_context();
+  test_default_ssl_roots();
 
   grpc_shutdown();
   return 0;