Rename stack-trace{.h,.cc,._test.cc} to use underscores

PiperOrigin-RevId: 257144753
Change-Id: I4ce0dffad552c25b61102adfb1c03b8aea427dd9

sandboxed_api/sandbox2/BUILD.bazel

@@ -261,13 +261,13 @@ cc_library(
         "monitor.h",
         "policybuilder.cc",
         "sandbox2.cc",
-        "stack-trace.cc",
+        "stack_trace.cc",
     ],
     hdrs = [
         "executor.h",
         "policybuilder.h",
         "sandbox2.h",
-        "stack-trace.h",
+        "stack_trace.h",
         # Workaround: reexporting the header files of our dependencies, see b/15420638
         "ipc.h",
         "limits.h",
@@ -717,8 +717,8 @@ cc_test(
 )
 
 cc_test(
-    name = "stack-trace_test",
-    srcs = ["stack-trace_test.cc"],
+    name = "stack_trace_test",
+    srcs = ["stack_trace_test.cc"],
     copts = sapi_platform_copts(),
     data = ["//sandboxed_api/sandbox2/testcases:symbolize"],
     deps = [

sandboxed_api/sandbox2/CMakeLists.txt

@@ -278,8 +278,8 @@ add_library(sandbox2_sandbox2 STATIC
   policybuilder.h
   sandbox2.cc
   sandbox2.h
-  stack-trace.cc
-  stack-trace.h
+  stack_trace.cc
+  stack_trace.h
 )
 add_library(sandbox2::sandbox2 ALIAS sandbox2_sandbox2)
 target_link_libraries(sandbox2_sandbox2
@@ -773,13 +773,13 @@ target_link_libraries(util_test PRIVATE
 gtest_discover_tests(util_test)
 
 # sandboxed_api/sandbox2:stack_trace_test
-add_executable(stack-trace_test
-  stack-trace_test.cc
+add_executable(stack_trace_test
+  stack_trace_test.cc
 )
-add_dependencies(stack-trace_test
+add_dependencies(stack_trace_test
   sandbox2::testcase_symbolize
 )
-target_link_libraries(stack-trace_test PRIVATE
+target_link_libraries(stack_trace_test PRIVATE
   absl::memory
   absl::strings
   sandbox2::bpf_helper
@@ -793,7 +793,7 @@ target_link_libraries(stack-trace_test PRIVATE
   sapi::status_matchers
   sapi::test_main
 )
-gtest_discover_tests(stack-trace_test PROPERTIES
+gtest_discover_tests(stack_trace_test PROPERTIES
   ENVIRONMENT "TEST_TMPDIR=/tmp"
   ENVIRONMENT "TEST_SRCDIR=${PROJECT_BINARY_DIR}"
 )

sandboxed_api/sandbox2/monitor.cc

@@ -57,7 +57,7 @@
 #include "sandboxed_api/sandbox2/regs.h"
 #include "sandboxed_api/sandbox2/result.h"
 #include "sandboxed_api/sandbox2/sanitizer.h"
-#include "sandboxed_api/sandbox2/stack-trace.h"
+#include "sandboxed_api/sandbox2/stack_trace.h"
 #include "sandboxed_api/sandbox2/syscall.h"
 #include "sandboxed_api/sandbox2/util.h"
 #include "sandboxed_api/util/raw_logging.h"

sandboxed_api/sandbox2/policybuilder.h

@@ -32,7 +32,6 @@
 #include "absl/strings/string_view.h"
 #include "sandboxed_api/sandbox2/mounts.h"
 #include "sandboxed_api/sandbox2/policy.h"
-#include "sandboxed_api/sandbox2/stack-trace.h"
 #include "sandboxed_api/util/statusor.h"
 
 struct bpf_labels;

sandboxed_api/sandbox2/stack_trace.cc

@@ -0,0 +1,322 @@
+// Copyright 2019 Google LLC. All Rights Reserved.
+//
+// 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.
+
+// Implementation of the sandbox2::StackTrace class.
+
+#include "sandboxed_api/sandbox2/stack_trace.h"
+
+#include <sys/capability.h>
+#include <sys/resource.h>
+#include <syscall.h>
+#include <memory>
+#include <utility>
+#include <vector>
+
+#include <glog/logging.h>
+#include "sandboxed_api/util/flag.h"
+#include "absl/memory/memory.h"
+#include "absl/strings/numbers.h"
+#include "absl/strings/str_cat.h"
+#include "absl/strings/strip.h"
+#include "libcap/include/sys/capability.h"
+#include "sandboxed_api/sandbox2/comms.h"
+#include "sandboxed_api/sandbox2/executor.h"
+#include "sandboxed_api/sandbox2/ipc.h"
+#include "sandboxed_api/sandbox2/limits.h"
+#include "sandboxed_api/sandbox2/policy.h"
+#include "sandboxed_api/sandbox2/policybuilder.h"
+#include "sandboxed_api/sandbox2/regs.h"
+#include "sandboxed_api/sandbox2/result.h"
+#include "sandboxed_api/sandbox2/sandbox2.h"
+#include "sandboxed_api/sandbox2/unwind/unwind.h"
+#include "sandboxed_api/sandbox2/unwind/unwind.pb.h"
+#include "sandboxed_api/sandbox2/util/bpf_helper.h"
+#include "sandboxed_api/sandbox2/util/fileops.h"
+#include "sandboxed_api/sandbox2/util/path.h"
+
+ABSL_FLAG(bool, sandbox_disable_all_stack_traces, false,
+          "Completely disable stack trace collection for sandboxees");
+
+ABSL_FLAG(bool, sandbox_libunwind_crash_handler, true,
+          "Sandbox libunwind when handling violations (preferred)");
+
+namespace sandbox2 {
+
+class StackTracePeer {
+ public:
+  static std::unique_ptr<Policy> GetPolicy(pid_t target_pid,
+                                           const std::string& maps_file,
+                                           const std::string& app_path,
+                                           const std::string& exe_path,
+                                           const Mounts& mounts);
+
+  static bool LaunchLibunwindSandbox(const Regs* regs, const Mounts& mounts,
+                                     UnwindResult* result,
+                                     const std::string& delim);
+};
+
+std::unique_ptr<Policy> StackTracePeer::GetPolicy(pid_t target_pid,
+                                                  const std::string& maps_file,
+                                                  const std::string& app_path,
+                                                  const std::string& exe_path,
+                                                  const Mounts& mounts) {
+  PolicyBuilder builder;
+  builder
+      // Use the mounttree of the original executable as starting point.
+      .SetMounts(mounts)
+      .AllowOpen()
+      .AllowRead()
+      .AllowWrite()
+      .AllowSyscall(__NR_close)
+      .AllowMmap()
+      .AllowExit()
+      .AllowHandleSignals()
+
+      // libunwind
+      .AllowSyscall(__NR_fstat)
+      .AllowSyscall(__NR_lseek)
+      .AllowSyscall(__NR_mincore)
+      .AllowSyscall(__NR_mprotect)
+      .AllowSyscall(__NR_munmap)
+      .AllowSyscall(__NR_pipe2)
+
+      // Symbolizer
+      .AllowSyscall(__NR_brk)
+      .AllowSyscall(__NR_clock_gettime)
+
+      // Other
+      .AllowSyscall(__NR_dup)
+      .AllowSyscall(__NR_fcntl)
+      .AllowSyscall(__NR_getpid)
+      .AllowSyscall(__NR_gettid)
+      .AllowSyscall(__NR_madvise)
+
+      // Required for our ptrace replacement.
+      .AddPolicyOnSyscall(
+          __NR_process_vm_readv,
+          {
+              // The pid technically is a 64bit int, however
+              // Linux usually uses max 16 bit, so we are fine
+              // with comparing only 32 bits here.
+              ARG_32(0),
+              JEQ32(static_cast<unsigned int>(target_pid), ALLOW),
+              JEQ32(static_cast<unsigned int>(1), ALLOW),
+          })
+
+      .EnableNamespaces()
+
+      // Add proc maps.
+      .AddFileAt(maps_file,
+                 file::JoinPath("/proc", absl::StrCat(target_pid), "maps"))
+      .AddFileAt(maps_file,
+                 file::JoinPath("/proc", absl::StrCat(target_pid), "task",
+                                absl::StrCat(target_pid), "maps"))
+
+      // Add the binary itself.
+      .AddFileAt(exe_path, app_path);
+
+  // Add all possible libraries without the need of parsing the binary
+  // or /proc/pid/maps.
+  for (const auto& library_path : {
+           "/usr/lib",
+           "/lib",
+       }) {
+    if (access(library_path, F_OK) != -1) {
+      VLOG(1) << "Adding library folder '" << library_path << "'";
+      builder.AddDirectory(library_path);
+    } else {
+      VLOG(1) << "Could not add library folder '" << library_path
+              << "' as it does not exist";
+    }
+  }
+
+  auto policy_or = builder.TryBuild();
+  if (!policy_or.ok()) {
+    LOG(ERROR) << "Creating stack unwinder sandbox policy failed";
+    return nullptr;
+  }
+  std::unique_ptr<Policy> policy = std::move(policy_or).ValueOrDie();
+  auto keep_capabilities = absl::make_unique<std::vector<cap_value_t>>();
+  keep_capabilities->push_back(CAP_SYS_PTRACE);
+  policy->AllowUnsafeKeepCapabilities(std::move(keep_capabilities));
+  // Use no special namespace flags when cloning. We will join an existing
+  // user namespace and will unshare() afterwards (See forkserver.cc).
+  policy->GetNamespace()->clone_flags_ = 0;
+  return policy;
+}
+
+bool StackTracePeer::LaunchLibunwindSandbox(const Regs* regs,
+                                            const Mounts& mounts,
+                                            sandbox2::UnwindResult* result,
+                                            const std::string& delim) {
+  const pid_t pid = regs->pid();
+
+  // Tell executor to use this special internal mode.
+  std::vector<std::string> argv;
+  std::vector<std::string> envp;
+
+  // We're not using absl::make_unique here as we're a friend of this specific
+  // constructor and using make_unique won't work.
+  auto executor = absl::WrapUnique(new Executor(pid));
+
+  executor->limits()
+      ->set_rlimit_as(RLIM64_INFINITY)
+      .set_rlimit_cpu(10)
+      .set_walltime_limit(absl::Seconds(5));
+
+  // Temporary directory used to provide files from /proc to the unwind sandbox.
+  char unwind_temp_directory_template[] = "/tmp/.sandbox2_unwind_XXXXXX";
+  char* unwind_temp_directory = mkdtemp(unwind_temp_directory_template);
+  if (!unwind_temp_directory) {
+    LOG(WARNING) << "Could not create temporary directory for unwinding";
+    return false;
+  }
+  struct UnwindTempDirectoryCleanup {
+    ~UnwindTempDirectoryCleanup() {
+      file_util::fileops::DeleteRecursively(capture);
+    }
+    char* capture;
+  } cleanup{unwind_temp_directory};
+
+  // Copy over important files from the /proc directory as we can't mount them.
+  const std::string unwind_temp_maps_path =
+      file::JoinPath(unwind_temp_directory, "maps");
+
+  if (!file_util::fileops::CopyFile(
+          file::JoinPath("/proc", absl::StrCat(pid), "maps"),
+          unwind_temp_maps_path, 0400)) {
+    LOG(WARNING) << "Could not copy maps file";
+    return false;
+  }
+
+  // Get path to the binary.
+  // app_path contains the path like it is also in /proc/pid/maps. This is
+  // important when the file was removed, it will have a ' (deleted)' suffix.
+  std::string app_path;
+  // The exe_path will have a mountable path of the application, even if it was
+  // removed.
+  std::string exe_path;
+  std::string proc_pid_exe = file::JoinPath("/proc", absl::StrCat(pid), "exe");
+  if (!file_util::fileops::ReadLinkAbsolute(proc_pid_exe, &app_path)) {
+    LOG(WARNING) << "Could not obtain absolute path to the binary";
+    return false;
+  }
+
+  // Check whether the file still exists or not (SAPI).
+  if (access(app_path.c_str(), F_OK) == -1) {
+    LOG(WARNING) << "File was removed, using /proc/pid/exe.";
+    app_path = std::string(absl::StripSuffix(app_path, " (deleted)"));
+    // Create a copy of /proc/pid/exe, mount that one.
+    exe_path = file::JoinPath(unwind_temp_directory, "exe");
+    if (!file_util::fileops::CopyFile(proc_pid_exe, exe_path, 0700)) {
+      LOG(WARNING) << "Could not copy /proc/pid/exe";
+      return false;
+    }
+  } else {
+    exe_path = app_path;
+  }
+
+  VLOG(1) << "Resolved binary: " << app_path << " / " << exe_path;
+
+  // Add mappings for the binary (as they might not have been added due to the
+  // forkserver).
+  auto policy = StackTracePeer::GetPolicy(pid, unwind_temp_maps_path, app_path,
+                                          exe_path, mounts);
+  if (!policy) {
+    return false;
+  }
+  auto comms = executor->ipc()->comms();
+  Sandbox2 s2(std::move(executor), std::move(policy));
+
+  VLOG(1) << "Running libunwind sandbox";
+  s2.RunAsync();
+  UnwindSetup msg;
+  msg.set_pid(pid);
+  msg.set_regs(reinterpret_cast<const char*>(&regs->user_regs_),
+               sizeof(regs->user_regs_));
+  msg.set_default_max_frames(kDefaultMaxFrames);
+  msg.set_delim(delim.c_str(), delim.size());
+
+  bool success = true;
+  if (!comms->SendProtoBuf(msg)) {
+    LOG(ERROR) << "Sending libunwind setup message failed";
+    success = false;
+  }
+
+  if (success && !comms->RecvProtoBuf(result)) {
+    LOG(ERROR) << "Receiving libunwind result failed";
+    success = false;
+  }
+
+  if (!success) {
+    s2.Kill();
+  }
+  auto s2_result = s2.AwaitResult();
+
+  LOG(INFO) << "Libunwind execution status: " << s2_result.ToString();
+
+  return success && s2_result.final_status() == Result::OK;
+}
+
+std::string GetStackTrace(const Regs* regs, const Mounts& mounts,
+                          const std::string& delim) {
+  if (absl::GetFlag(FLAGS_sandbox_disable_all_stack_traces)) {
+    return "";
+  }
+  if (!regs) {
+    LOG(WARNING) << "Could not obtain stacktrace, regs == nullptr";
+    return "[ERROR (noregs)]";
+  }
+
+#if defined(THREAD_SANITIZER) || defined(ADDRESS_SANITIZER) || \
+    defined(MEMORY_SANITIZER)
+  constexpr bool kSanitizerEnabled = true;
+#else
+  constexpr bool kSanitizerEnabled = false;
+#endif
+
+  const bool coverage_enabled =
+      getenv("COVERAGE");
+
+  // Show a warning if sandboxed libunwind is requested but we're running in
+  // an ASAN / coverage build (= we can't use sandboxed libunwind).
+  if (absl::GetFlag(FLAGS_sandbox_libunwind_crash_handler) &&
+      (kSanitizerEnabled || coverage_enabled)) {
+    LOG_IF(WARNING, kSanitizerEnabled)
+        << "Sanitizer build, using non-sandboxed libunwind";
+    LOG_IF(WARNING, coverage_enabled)
+        << "Coverage build, using non-sandboxed libunwind";
+    return UnsafeGetStackTrace(regs->pid(), delim);
+  }
+
+  if (!absl::GetFlag(FLAGS_sandbox_libunwind_crash_handler)) {
+    return UnsafeGetStackTrace(regs->pid(), delim);
+  }
+  UnwindResult res;
+
+  if (!StackTracePeer::LaunchLibunwindSandbox(regs, mounts, &res, delim)) {
+    return "";
+  }
+  return res.stacktrace();
+}
+
+std::string UnsafeGetStackTrace(pid_t pid, const std::string& delim) {
+  LOG(WARNING) << "Using non-sandboxed libunwind";
+  std::string stack_trace;
+  std::vector<uintptr_t> ips;
+  RunLibUnwindAndSymbolizer(pid, &stack_trace, &ips, kDefaultMaxFrames, delim);
+  return stack_trace;
+}
+
+}  // namespace sandbox2

sandboxed_api/sandbox2/stack_trace.h

@@ -0,0 +1,47 @@
+// Copyright 2019 Google LLC. All Rights Reserved.
+//
+// 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.
+
+// The sandbox2::StackTrace class provides static methods useful when analyzing
+// call-stack of the process. It uses libunwind-ptrace, so the process must be
+// in a stopped state to call those methods.
+
+#ifndef SANDBOXED_API_SANDBOX2_STACK_TRACE_H_
+#define SANDBOXED_API_SANDBOX2_STACK_TRACE_H_
+
+#include <sys/types.h>
+#include <cstddef>
+#include <memory>
+#include <string>
+
+#include "sandboxed_api/sandbox2/mounts.h"
+#include "sandboxed_api/sandbox2/policy.h"
+#include "sandboxed_api/sandbox2/regs.h"
+#include "sandboxed_api/sandbox2/unwind/unwind.pb.h"
+
+namespace sandbox2 {
+
+// Maximum depth of analyzed call stack.
+constexpr size_t kDefaultMaxFrames = 200;
+
+// Returns the stack-trace of the PID=pid, delimited by the delim argument.
+std::string GetStackTrace(const Regs* regs, const Mounts& mounts,
+                          const std::string& delim = " ");
+
+// Similar to GetStackTrace() but without using the sandbox to isolate
+// libunwind.
+std::string UnsafeGetStackTrace(pid_t pid, const std::string& delim = " ");
+
+}  // namespace sandbox2
+
+#endif  // SANDBOXED_API_SANDBOX2_STACK_TRACE_H_

sandboxed_api/sandbox2/stack_trace_test.cc

@@ -0,0 +1,196 @@
+// Copyright 2019 Google LLC. All Rights Reserved.
+//
+// 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.
+
+#include "sandboxed_api/sandbox2/stack_trace.h"
+
+#include <dirent.h>
+
+#include <cstdio>
+#include <utility>
+
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+#include "sandboxed_api/util/flag.h"
+#include "absl/memory/memory.h"
+#include "absl/strings/match.h"
+#include "absl/strings/str_cat.h"
+#include "sandboxed_api/sandbox2/executor.h"
+#include "sandboxed_api/sandbox2/global_forkclient.h"
+#include "sandboxed_api/sandbox2/policy.h"
+#include "sandboxed_api/sandbox2/policybuilder.h"
+#include "sandboxed_api/sandbox2/result.h"
+#include "sandboxed_api/sandbox2/sandbox2.h"
+#include "sandboxed_api/sandbox2/testing.h"
+#include "sandboxed_api/sandbox2/util/bpf_helper.h"
+#include "sandboxed_api/sandbox2/util/fileops.h"
+#include "sandboxed_api/sandbox2/util/temp_file.h"
+#include "sandboxed_api/util/status_matchers.h"
+
+ABSL_DECLARE_FLAG(bool, sandbox_libunwind_crash_handler);
+
+using ::testing::Eq;
+using ::testing::HasSubstr;
+using ::testing::Not;
+
+namespace sandbox2 {
+namespace {
+
+// Temporarily overrides a flag, restores the original flag value when it goes
+// out of scope.
+template <typename T>
+class TemporaryFlagOverride {
+ public:
+  using Flag = T;
+  TemporaryFlagOverride(Flag* flag, T value)
+      : flag_(flag), original_value_(absl::GetFlag(*flag)) {
+    absl::SetFlag(flag, value);
+  }
+
+  ~TemporaryFlagOverride() { absl::SetFlag(flag_, original_value_); }
+
+ private:
+  Flag* flag_;
+  T original_value_;
+};
+
+// Test that symbolization of stack traces works.
+void SymbolizationWorksCommon(
+    const std::function<void(PolicyBuilder*)>& modify_policy) {
+  const std::string path = GetTestSourcePath("sandbox2/testcases/symbolize");
+  std::vector<std::string> args = {path, "1"};
+  auto executor = absl::make_unique<Executor>(path, args);
+
+  std::string temp_filename = CreateNamedTempFileAndClose("/tmp/").ValueOrDie();
+  file_util::fileops::CopyFile("/proc/cpuinfo", temp_filename, 0444);
+  struct TempCleanup {
+    ~TempCleanup() { remove(capture->c_str()); }
+    std::string* capture;
+  } temp_cleanup{&temp_filename};
+
+  PolicyBuilder policybuilder;
+  policybuilder
+      // Don't restrict the syscalls at all.
+      .DangerDefaultAllowAll()
+      .EnableNamespaces()
+      .AddFile(path)
+      .AddLibrariesForBinary(path)
+      .AddFileAt(temp_filename, "/proc/cpuinfo");
+
+  modify_policy(&policybuilder);
+  SAPI_ASSERT_OK_AND_ASSIGN(auto policy, policybuilder.TryBuild());
+
+  Sandbox2 s2(std::move(executor), std::move(policy));
+  auto result = s2.Run();
+
+  ASSERT_THAT(result.final_status(), Eq(Result::SIGNALED));
+  ASSERT_THAT(result.GetStackTrace(), HasSubstr("CrashMe"));
+  // Check that demangling works as well.
+  ASSERT_THAT(result.GetStackTrace(), HasSubstr("CrashMe()"));
+}
+
+TEST(StackTraceTest, SymbolizationWorksNonSandboxedLibunwind) {
+  SKIP_SANITIZERS_AND_COVERAGE;
+  TemporaryFlagOverride<bool> temp_override(
+      &FLAGS_sandbox_libunwind_crash_handler, false);
+  SymbolizationWorksCommon([](PolicyBuilder*) {});
+}
+
+TEST(StackTraceTest, SymbolizationWorksSandboxedLibunwind) {
+  SKIP_SANITIZERS_AND_COVERAGE;
+  TemporaryFlagOverride<bool> temp_override(
+      &FLAGS_sandbox_libunwind_crash_handler, true);
+  SymbolizationWorksCommon([](PolicyBuilder*) {});
+}
+
+TEST(StackTraceTest, SymbolizationWorksSandboxedLibunwindProcDirMounted) {
+  SKIP_SANITIZERS_AND_COVERAGE;
+  TemporaryFlagOverride<bool> temp_override(
+      &FLAGS_sandbox_libunwind_crash_handler, true);
+  SymbolizationWorksCommon(
+      [](PolicyBuilder* builder) { builder->AddDirectory("/proc"); });
+}
+
+TEST(StackTraceTest, SymbolizationWorksSandboxedLibunwindProcFileMounted) {
+  SKIP_SANITIZERS_AND_COVERAGE;
+  TemporaryFlagOverride<bool> temp_override(
+      &FLAGS_sandbox_libunwind_crash_handler, true);
+  SymbolizationWorksCommon([](PolicyBuilder* builder) {
+    builder->AddFile("/proc/sys/vm/overcommit_memory");
+  });
+}
+
+TEST(StackTraceTest, SymbolizationWorksSandboxedLibunwindSysDirMounted) {
+  SKIP_SANITIZERS_AND_COVERAGE;
+  TemporaryFlagOverride<bool> temp_override(
+      &FLAGS_sandbox_libunwind_crash_handler, true);
+  SymbolizationWorksCommon(
+      [](PolicyBuilder* builder) { builder->AddDirectory("/sys"); });
+}
+
+TEST(StackTraceTest, SymbolizationWorksSandboxedLibunwindSysFileMounted) {
+  SKIP_SANITIZERS_AND_COVERAGE;
+  TemporaryFlagOverride<bool> temp_override(
+      &FLAGS_sandbox_libunwind_crash_handler, true);
+  SymbolizationWorksCommon([](PolicyBuilder* builder) {
+    builder->AddFile("/sys/devices/system/cpu/online");
+  });
+}
+
+static size_t FileCountInDirectory(const std::string& path) {
+  std::vector<std::string> fds;
+  std::string error;
+  CHECK(file_util::fileops::ListDirectoryEntries(path, &fds, &error));
+  return fds.size();
+}
+
+TEST(StackTraceTest, ForkEnterNsLibunwindDoesNotLeakFDs) {
+  SKIP_SANITIZERS_AND_COVERAGE;
+  // Get list of open FDs in the global forkserver.
+  pid_t forkserver_pid = GetGlobalForkServerPid();
+  std::string forkserver_fd_path =
+      absl::StrCat("/proc/", forkserver_pid, "/fd");
+  size_t filecount_before = FileCountInDirectory(forkserver_fd_path);
+
+  TemporaryFlagOverride<bool> temp_override(
+      &FLAGS_sandbox_libunwind_crash_handler, true);
+  SymbolizationWorksCommon([](PolicyBuilder* builder) {
+    builder->AddFile("/sys/devices/system/cpu/online");
+  });
+
+  EXPECT_THAT(filecount_before, Eq(FileCountInDirectory(forkserver_fd_path)));
+}
+
+// Test that symbolization skips writeable files (attack vector).
+TEST(StackTraceTest, SymbolizationTrustedFilesOnly) {
+  SKIP_SANITIZERS_AND_COVERAGE;
+  const std::string path = GetTestSourcePath("sandbox2/testcases/symbolize");
+  std::vector<std::string> args = {path, "2"};
+  auto executor = absl::make_unique<Executor>(path, args);
+  SAPI_ASSERT_OK_AND_ASSIGN(auto policy, PolicyBuilder{}
+                                        // Don't restrict the syscalls at all.
+                                        .DangerDefaultAllowAll()
+                                        .EnableNamespaces()
+                                        .AddFile(path)
+                                        .AddLibrariesForBinary(path)
+                                        .TryBuild());
+
+  Sandbox2 s2(std::move(executor), std::move(policy));
+  auto result = s2.Run();
+
+  ASSERT_THAT(result.final_status(), Eq(Result::SIGNALED));
+  ASSERT_THAT(result.GetStackTrace(), Not(HasSubstr("CrashMe")));
+}
+
+}  // namespace
+}  // namespace sandbox2