Linux sandbox: add basic Yama support

sandbox/linux/services/yama.h

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef SANDBOX_LINUX_SERVICES_YAMA_H_
+#define SANDBOX_LINUX_SERVICES_YAMA_H_
+
+#include "base/basictypes.h"
+#include "base/process/process_handle.h"
+
+namespace sandbox {
+
+// Yama is a LSM kernel module which can restrict ptrace().
+// This class provides ways to detect if Yama is present and enabled
+// and to restrict which processes can ptrace the current process.
+class Yama {
+ public:
+  // This enum should be used to set or check a bitmask.
+  // A value of 0 would indicate that the status is not known.
+  enum GlobalStatus {
+    STATUS_KNOWN = 1 << 0,
+    STATUS_PRESENT = 1 << 1,
+    STATUS_ENFORCING = 1 << 2,
+    // STATUS_STRICT_ENFORCING corresponds to either mode 2 or mode 3 of Yama.
+    // Ptrace could be entirely denied, or restricted to CAP_SYS_PTRACE
+    // and PTRACE_TRACEME.
+    STATUS_STRICT_ENFORCING = 1 << 3
+  };
+
+  // Restrict who can ptrace() the current process to its ancestors.
+  // If this succeeds, then Yama is available on this kernel.
+  // However, Yama may not be enforcing at this time.
+  static bool RestrictPtracersToAncestors();
+
+  // Disable Yama restrictions for the current process.
+  // This will fail if Yama is not available on this kernel.
+  // This is meant for testing only. If you need this, implement
+  // a per-pid authorization instead.
+  static bool DisableYamaRestrictions();
+
+  // Checks if Yama is currently in enforcing mode for the machine (not the
+  // current process). This requires access to the filesystem and will use
+  // /proc/sys/kernel/yama/ptrace_scope.
+  static int GetStatus();
+
+  // Helper for checking for STATUS_PRESENT in GetStatus().
+  static bool IsPresent();
+  // Helper for checkking for STATUS_ENFORCING in GetStatus().
+  static bool IsEnforcing();
+
+ private:
+  DISALLOW_IMPLICIT_CONSTRUCTORS(Yama);
+};
+
+}  // namespace sandbox
+
+#endif  // SANDBOX_LINUX_SERVICES_YAMA_H_