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sandboxed-api/sandboxed_api/sandbox2/stack_trace.cc

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// Copyright 2019 Google LLC
//
// 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
//
// https://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/resource.h>
#include <syscall.h>
#include <memory>
#include <utility>
#include <vector>
#include "absl/cleanup/cleanup.h"
#include "absl/flags/flag.h"
#include "absl/log/log.h"
#include "absl/memory/memory.h"
#include "absl/status/status.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/config.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/util/fileops.h"
#include "sandboxed_api/util/path.h"
#include "sandboxed_api/util/raw_logging.h"
#include "sandboxed_api/util/status_macros.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 {
namespace {
namespace file = ::sapi::file;
namespace file_util = ::sapi::file_util;
// Similar to GetStackTrace() but without using the sandbox to isolate
// libunwind.
absl::StatusOr<std::vector<std::string>> UnsafeGetStackTrace(pid_t pid) {
LOG(WARNING) << "Using non-sandboxed libunwind";
return RunLibUnwindAndSymbolizer(pid, kDefaultMaxFrames);
}
} // namespace
class StackTracePeer {
public:
static absl::StatusOr<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 absl::StatusOr<UnwindResult> LaunchLibunwindSandbox(
const Regs* regs, const Mounts& mounts);
};
absl::StatusOr<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
.AllowStat()
.AllowSyscall(__NR_lseek)
#ifdef __NR__llseek
.AllowSyscall(__NR__llseek) // Newer glibc on PPC
#endif
.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.
.TrapPtrace()
.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),
})
// 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/lib64",
"/usr/lib",
"/lib64",
"/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";
}
}
SAPI_ASSIGN_OR_RETURN(std::unique_ptr<Policy> policy, builder.TryBuild());
policy->AllowUnsafeKeepCapabilities({CAP_SYS_PTRACE});
// 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 std::move(policy);
}
absl::StatusOr<UnwindResult> StackTracePeer::LaunchLibunwindSandbox(
const Regs* regs, const Mounts& mounts) {
const pid_t pid = regs->pid();
// Tell executor to use this special internal mode. Using `new` to access a
// non-public constructor.
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) {
return absl::InternalError(
"Could not create temporary directory for unwinding");
}
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)) {
return absl::InternalError("Could not copy maps file");
}
// Get path to the binary.
// app_path contains the path like it is also in /proc/pid/maps. It is
// relative to the sandboxee's mount namespace. If it is not existing
// (anymore) it will have a ' (deleted)' suffix.
std::string app_path;
std::string proc_pid_exe = file::JoinPath("/proc", absl::StrCat(pid), "exe");
if (!file_util::fileops::ReadLinkAbsolute(proc_pid_exe, &app_path)) {
return absl::InternalError("Could not obtain absolute path to the binary");
}
// The exe_path will have a mountable path of the application, even if it was
// removed.
// Resolve app_path backing file.
std::string exe_path = mounts.ResolvePath(app_path).value_or("");
if (exe_path.empty()) {
// File was probably removed.
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)) {
return absl::InternalError("Could not copy /proc/pid/exe");
}
}
VLOG(1) << "Resolved binary: " << app_path << " / " << exe_path;
// Add mappings for the binary (as they might not have been added due to the
// forkserver).
SAPI_ASSIGN_OR_RETURN(std::unique_ptr<Policy> policy,
StackTracePeer::GetPolicy(pid, unwind_temp_maps_path,
app_path, exe_path, mounts));
Sandbox2 sandbox(std::move(executor), std::move(policy));
VLOG(1) << "Running libunwind sandbox";
sandbox.RunAsync();
Comms* comms = sandbox.comms();
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);
absl::Cleanup kill_sandbox = [&sandbox]() {
sandbox.Kill();
sandbox.AwaitResult().IgnoreResult();
};
if (!comms->SendProtoBuf(msg)) {
return absl::InternalError("Sending libunwind setup message failed");
}
absl::Status status;
if (!comms->RecvStatus(&status)) {
return absl::InternalError(
"Receiving status from libunwind sandbox failed");
}
SAPI_RETURN_IF_ERROR(status);
UnwindResult result;
if (!comms->RecvProtoBuf(&result)) {
return absl::InternalError("Receiving libunwind result failed");
}
std::move(kill_sandbox).Cancel();
auto sandbox_result = sandbox.AwaitResult();
LOG(INFO) << "Libunwind execution status: " << sandbox_result.ToString();
if (sandbox_result.final_status() != Result::OK) {
return absl::InternalError(
absl::StrCat("libunwind sandbox did not finish properly: ",
sandbox_result.ToString()));
}
return result;
}
absl::StatusOr<std::vector<std::string>> GetStackTrace(const Regs* regs,
const Mounts& mounts) {
if (absl::GetFlag(FLAGS_sandbox_disable_all_stack_traces)) {
return absl::UnavailableError("Stacktraces disabled");
}
if (!regs) {
return absl::InvalidArgumentError(
"Could not obtain stacktrace, regs == nullptr");
}
// Show a warning if sandboxed libunwind is requested but we're running in
// an ASAN/coverage build (= we can't use sandboxed libunwind).
if (const bool coverage_enabled =
getenv("COVERAGE") != nullptr;
absl::GetFlag(FLAGS_sandbox_libunwind_crash_handler) &&
(sapi::sanitizers::IsAny() || coverage_enabled)) {
LOG_IF(WARNING, sapi::sanitizers::IsAny())
<< "Sanitizer build, using non-sandboxed libunwind";
LOG_IF(WARNING, coverage_enabled)
<< "Coverage build, using non-sandboxed libunwind";
return UnsafeGetStackTrace(regs->pid());
}
if (!absl::GetFlag(FLAGS_sandbox_libunwind_crash_handler)) {
return UnsafeGetStackTrace(regs->pid());
}
SAPI_ASSIGN_OR_RETURN(UnwindResult res,
StackTracePeer::LaunchLibunwindSandbox(regs, mounts));
return std::vector<std::string>(res.stacktrace().begin(),
res.stacktrace().end());
}
std::vector<std::string> CompactStackTrace(
const std::vector<std::string>& stack_trace) {
std::vector<std::string> compact_trace;
compact_trace.reserve(stack_trace.size() / 2);
const std::string* prev = nullptr;
int seen = 0;
auto add_repeats = [&compact_trace](int seen) {
if (seen != 0) {
compact_trace.push_back(
absl::StrCat("(previous frame repeated ", seen, " times)"));
}
};
for (const auto& frame : stack_trace) {
if (prev && frame == *prev) {
++seen;
} else {
prev = &frame;
add_repeats(seen);
seen = 0;
compact_trace.push_back(frame);
}
}
add_repeats(seen);
return compact_trace;
}
} // namespace sandbox2
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