sandbox/linux/services/yama_unittests.cc

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include <errno.h>
   6 #include <fcntl.h>
   7 #include <sys/ptrace.h>
   8 #include <sys/stat.h>
   9 #include <sys/types.h>
  10 #include <unistd.h>
  11
  12 #include "base/bind.h"
  13 #include "base/compiler_specific.h"
  14 #include "base/posix/eintr_wrapper.h"
  15 #include "base/strings/string_util.h"
  16 #include "base/sys_info.h"
  17 #include "sandbox/linux/services/scoped_process.h"
  18 #include "sandbox/linux/services/yama.h"
  19 #include "sandbox/linux/tests/unit_tests.h"
  20 #include "testing/gtest/include/gtest/gtest.h"
  21
  22 namespace sandbox {
  23
  24 namespace {
  25
  26 bool HasLinux32Bug() {
  27 #if defined(__i386__)
  28   // On 3.2 kernels, yama doesn't work for 32-bit binaries on 64-bit kernels.
  29   // This is fixed in 3.4.
  30   bool is_kernel_64bit =
  31       base::SysInfo::OperatingSystemArchitecture() == "x86_64";
  32   bool is_linux = base::SysInfo::OperatingSystemName() == "Linux";
  33   bool is_3_dot_2 = StartsWithASCII(
  34       base::SysInfo::OperatingSystemVersion(), "3.2", /*case_sensitive=*/false);
  35   if (is_kernel_64bit && is_linux && is_3_dot_2)
  36     return true;
  37 #endif  // defined(__i386__)
  38   return false;
  39 }
  40
  41 bool CanPtrace(pid_t pid) {
  42   int ret;
  43   ret = ptrace(PTRACE_ATTACH, pid, NULL, NULL);
  44   if (ret == -1) {
  45     CHECK_EQ(EPERM, errno);
  46     return false;
  47   }
  48   // Wait for the process to be stopped so that it can be detached.
  49   siginfo_t process_info;
  50   int wait_ret = HANDLE_EINTR(waitid(P_PID, pid, &process_info, WSTOPPED));
  51   PCHECK(0 == wait_ret);
  52   PCHECK(0 == ptrace(PTRACE_DETACH, pid, NULL, NULL));
  53   return true;
  54 }
  55
  56 // _exit(0) if pid can be ptraced by the current process.
  57 // _exit(1) otherwise.
  58 void ExitZeroIfCanPtrace(pid_t pid) {
  59   if (CanPtrace(pid)) {
  60     _exit(0);
  61   } else {
  62     _exit(1);
  63   }
  64 }
  65
  66 bool CanSubProcessPtrace(pid_t pid) {
  67   ScopedProcess process(base::Bind(&ExitZeroIfCanPtrace, pid));
  68   bool signaled;
  69   int exit_code = process.WaitForExit(&signaled);
  70   CHECK(!signaled);
  71   return 0 == exit_code;
  72 }
  73
  74 // The tests below assume that the system-level configuration will not change
  75 // while they run.
  76
  77 TEST(Yama, GetStatus) {
  78   int status1 = Yama::GetStatus();
  79
  80   // Check that the value is a possible bitmask.
  81   ASSERT_LE(0, status1);
  82   ASSERT_GE(Yama::STATUS_KNOWN | Yama::STATUS_PRESENT | Yama::STATUS_ENFORCING |
  83                 Yama::STATUS_STRICT_ENFORCING,
  84             status1);
  85
  86   // The status should not just be a random value.
  87   int status2 = Yama::GetStatus();
  88   EXPECT_EQ(status1, status2);
  89
  90   // This test is not running sandboxed, there is no reason to not know the
  91   // status.
  92   EXPECT_NE(0, Yama::STATUS_KNOWN & status1);
  93
  94   if (status1 & Yama::STATUS_STRICT_ENFORCING) {
  95     // If Yama is strictly enforcing, it is also enforcing.
  96     EXPECT_TRUE(status1 & Yama::STATUS_ENFORCING);
  97   }
  98
  99   if (status1 & Yama::STATUS_ENFORCING) {
 100     // If Yama is enforcing, Yama is present.
 101     EXPECT_NE(0, status1 & Yama::STATUS_PRESENT);
 102   }
 103
 104   // Verify that the helper functions work as intended.
 105   EXPECT_EQ(static_cast<bool>(status1 & Yama::STATUS_ENFORCING),
 106             Yama::IsEnforcing());
 107   EXPECT_EQ(static_cast<bool>(status1 & Yama::STATUS_PRESENT),
 108             Yama::IsPresent());
 109
 110   fprintf(stdout,
 111           "Yama present: %s - enforcing: %s\n",
 112           Yama::IsPresent() ? "Y" : "N",
 113           Yama::IsEnforcing() ? "Y" : "N");
 114 }
 115
 116 SANDBOX_TEST(Yama, RestrictPtraceSucceedsWhenYamaPresent) {
 117   // This call will succeed iff Yama is present.
 118   bool restricted = Yama::RestrictPtracersToAncestors();
 119   CHECK_EQ(restricted, Yama::IsPresent());
 120 }
 121
 122 // Attempts to enable or disable Yama restrictions.
 123 void SetYamaRestrictions(bool enable_restriction) {
 124   if (enable_restriction) {
 125     Yama::RestrictPtracersToAncestors();
 126   } else {
 127     Yama::DisableYamaRestrictions();
 128   }
 129 }
 130
 131 TEST(Yama, RestrictPtraceWorks) {
 132   if (HasLinux32Bug())
 133     return;
 134
 135   ScopedProcess process1(base::Bind(&SetYamaRestrictions, true));
 136   ASSERT_TRUE(process1.WaitForClosureToRun());
 137
 138   if (Yama::IsEnforcing()) {
 139     // A sibling process cannot ptrace process1.
 140     ASSERT_FALSE(CanSubProcessPtrace(process1.GetPid()));
 141   }
 142
 143   if (!(Yama::GetStatus() & Yama::STATUS_STRICT_ENFORCING)) {
 144     // However, parent can ptrace process1.
 145     ASSERT_TRUE(CanPtrace(process1.GetPid()));
 146
 147     // A sibling can ptrace process2 which disables any Yama protection.
 148     ScopedProcess process2(base::Bind(&SetYamaRestrictions, false));
 149     ASSERT_TRUE(process2.WaitForClosureToRun());
 150     ASSERT_TRUE(CanSubProcessPtrace(process2.GetPid()));
 151   }
 152 }
 153
 154 void DoNothing() {}
 155
 156 SANDBOX_TEST(Yama, RestrictPtraceIsDefault) {
 157   if (!Yama::IsPresent() || HasLinux32Bug())
 158     return;
 159
 160   CHECK(Yama::DisableYamaRestrictions());
 161   ScopedProcess process1(base::Bind(&DoNothing));
 162
 163   if (Yama::IsEnforcing()) {
 164     // Check that process1 is protected by Yama, even though it has
 165     // been created from a process that disabled Yama.
 166     CHECK(!CanSubProcessPtrace(process1.GetPid()));
 167   }
 168 }
 169
 170 }  // namespace
 171
 172 }  // namespace sandbox