Linux sandbox: add basic Yama support

sandbox/linux/services/yama_unittests.cc

+// 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.
+
+#include <errno.h>
+#include <fcntl.h>
+#include <sys/ptrace.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include "base/bind.h"
+#include "base/compiler_specific.h"
+#include "base/posix/eintr_wrapper.h"
+#include "sandbox/linux/services/scoped_process.h"
+#include "sandbox/linux/services/yama.h"
+#include "sandbox/linux/tests/unit_tests.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace sandbox {
+
+namespace {
+
+bool CanPtrace(pid_t pid) {
+  int ret;
+  ret = ptrace(PTRACE_ATTACH, pid, NULL, NULL);
+  if (ret == -1) {
+    CHECK_EQ(EPERM, errno);
+    return false;
+  }
+  // Wait for the process to be stopped so that it can be detached.
+  siginfo_t process_info;
+  int wait_ret = HANDLE_EINTR(waitid(P_PID, pid, &process_info, WSTOPPED));
+  PCHECK(0 == wait_ret);
+  PCHECK(0 == ptrace(PTRACE_DETACH, pid, NULL, NULL));
+  return true;
+}
+
+// _exit(0) if pid can be ptraced by the current process.
+// _exit(1) otherwise.
+void ExitZeroIfCanPtrace(pid_t pid) {
+  if (CanPtrace(pid)) {
+    _exit(0);
+  } else {
+    _exit(1);
+  }
+}
+
+bool CanSubProcessPtrace(pid_t pid) {
+  ScopedProcess process(base::Bind(&ExitZeroIfCanPtrace, pid));
+  bool signaled;
+  int exit_code = process.WaitForExit(&signaled);
+  CHECK(!signaled);
+  return 0 == exit_code;
+}
+
+// The tests below assume that the system-level configuration will not change
+// while they run.
+
+TEST(Yama, GetStatus) {
+  int status1 = Yama::GetStatus();
+
+  // Check that the value is a possible bitmask.
+  ASSERT_LE(0, status1);
+  ASSERT_GE(Yama::STATUS_KNOWN | Yama::STATUS_PRESENT | Yama::STATUS_ENFORCING |
+                Yama::STATUS_STRICT_ENFORCING,
+            status1);
+
+  // The status should not just be a random value.
+  int status2 = Yama::GetStatus();
+  EXPECT_EQ(status1, status2);
+
+  // This test is not running sandboxed, there is no reason to not know the
+  // status.
+  EXPECT_NE(0, Yama::STATUS_KNOWN & status1);
+
+  if (status1 & Yama::STATUS_STRICT_ENFORCING) {
+    // If Yama is strictly enforcing, it is also enforcing.
+    EXPECT_TRUE(status1 & Yama::STATUS_ENFORCING);
+  }
+
+  if (status1 & Yama::STATUS_ENFORCING) {
+    // If Yama is enforcing, Yama is present.
+    EXPECT_NE(0, status1 & Yama::STATUS_PRESENT);
+  }
+
+  // Verify that the helper functions work as intended.
+  EXPECT_EQ(static_cast<bool>(status1 & Yama::STATUS_ENFORCING),
+            Yama::IsEnforcing());
+  EXPECT_EQ(static_cast<bool>(status1 & Yama::STATUS_PRESENT),
+            Yama::IsPresent());
+
+  fprintf(stdout,
+          "Yama present: %s - enforcing: %s\n",
+          Yama::IsPresent() ? "Y" : "N",
+          Yama::IsEnforcing() ? "Y" : "N");
+}
+
+SANDBOX_TEST(Yama, RestrictPtraceSucceedsWhenYamaPresent) {
+  // This call will succeed iff Yama is present.
+  bool restricted = Yama::RestrictPtracersToAncestors();
+  CHECK_EQ(restricted, Yama::IsPresent());
+}
+
+// Attempts to enable or disable Yama restrictions.
+void SetYamaRestrictions(bool enable_restriction) {
+  if (enable_restriction) {
+    Yama::RestrictPtracersToAncestors();
+  } else {
+    Yama::DisableYamaRestrictions();
+  }
+}
+
+TEST(Yama, RestrictPtraceWorks) {
+  ScopedProcess process1(base::Bind(&SetYamaRestrictions, true));
+  ASSERT_TRUE(process1.WaitForClosureToRun());
+
+  if (Yama::IsEnforcing()) {
+    // A sibling process cannot ptrace process1.
+    ASSERT_FALSE(CanSubProcessPtrace(process1.GetPid()));
+  }
+
+  if (!(Yama::GetStatus() & Yama::STATUS_STRICT_ENFORCING)) {
+    // However, parent can ptrace process1.
+    ASSERT_TRUE(CanPtrace(process1.GetPid()));
+
+    // A sibling can ptrace process2 which disables any Yama protection.
+    ScopedProcess process2(base::Bind(&SetYamaRestrictions, false));
+    ASSERT_TRUE(process2.WaitForClosureToRun());
+    ASSERT_TRUE(CanSubProcessPtrace(process2.GetPid()));
+  }
+}
+
+void DoNothing() {}
+
+SANDBOX_TEST(Yama, RestrictPtraceIsDefault) {
+  if (!Yama::IsPresent())
+    return;
+
+  CHECK(Yama::DisableYamaRestrictions());
+  ScopedProcess process1(base::Bind(&DoNothing));
+
+  if (Yama::IsEnforcing()) {
+    // Check that process1 is protected by Yama, even though it has
+    // been created from a process that disabled Yama.
+    CHECK(!CanSubProcessPtrace(process1.GetPid()));
+  }
+}
+
+}  // namespace
+
+}  // namespace sandbox