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Christian Blichmann 2019-07-09 01:08:31 -07:00 committed by Copybara-Service
parent c7f7666d9d
commit 2da6dad120
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322
sandboxed_api/sandbox2/stack-trace.cc
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// 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

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sandboxed_api/sandbox2/stack-trace.h
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// 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__

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sandboxed_api/sandbox2/stack-trace_test.cc
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// 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 <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/stack-trace.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