init: setup keyring before ueventd starts

Invent keyutils.h to supply capability to set session keyring.
The keyring will hold things like the FBE encryption keys.

Test: gTest logd-unit-tests --gtest_filter=logd.statistics
Bug: 37751120
Bug: 36645158
Change-Id: Ieb44fa8f53dda6cf506a6243498c72d7f7f3cde7

init/init.cpp

@@ -21,6 +21,7 @@
 #include <errno.h>
 #include <fcntl.h>
 #include <inttypes.h>
+#include <keyutils.h>
 #include <libgen.h>
 #include <paths.h>
 #include <signal.h>
@@ -1015,6 +1016,11 @@ int main(int argc, char** argv) {
     InitKernelLogging(argv);
     LOG(INFO) << "init second stage started!";
 
+    // Set up a session keyring that all processes will have access to. It
+    // will hold things like FBE encryption keys. No process should override
+    // its session keyring.
+    keyctl(KEYCTL_GET_KEYRING_ID, KEY_SPEC_SESSION_KEYRING, 1);
+
     // Indicate that booting is in progress to background fw loaders, etc.
     close(open("/dev/.booting", O_WRONLY | O_CREAT | O_CLOEXEC, 0000));
 

init/keyutils.h

+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/* Miniature version of a header-only keyutils.h (no library required) */
+
+#ifndef _INIT_KEYUTILS_H_
+#define _INIT_KEYUTILS_H_
+
+#ifndef KEYUTILS_H /* walk away if the _real_ one exists */
+
+#include <linux/keyctl.h>
+#include <stdarg.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+static inline long keyctl(int cmd, ...) {
+    va_list va;
+    unsigned long arg2, arg3, arg4, arg5;
+
+    va_start(va, cmd);
+    arg2 = va_arg(va, unsigned long);
+    arg3 = va_arg(va, unsigned long);
+    arg4 = va_arg(va, unsigned long);
+    arg5 = va_arg(va, unsigned long);
+    va_end(va);
+    return syscall(__NR_keyctl, cmd, arg2, arg3, arg4, arg5);
+}
+
+#endif
+
+#endif