sandboxed-api/sandboxed_api/sandbox2/util.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
//
// 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/util.h"
#include <asm/unistd.h> // __NR_memdfd_create
#include <bits/local_lim.h>
#include <sched.h>
#include <spawn.h>
#include <sys/resource.h>
#include <sys/stat.h>
#include <sys/uio.h>
#include <sys/wait.h>
#include <unistd.h>
#include <array>
#include <cerrno>
#include <csetjmp>
#include <cstddef>
#include <cstdint>
#include <cstring>
#include <memory>
#include "absl/base/attributes.h"
#include "absl/strings/escaping.h"
#include "absl/strings/numbers.h"
#include "absl/strings/str_cat.h"
#include "absl/strings/str_format.h"
#include "absl/strings/string_view.h"
#include "absl/strings/strip.h"
#include "sandboxed_api/sandbox2/util/fileops.h"
#include "sandboxed_api/sandbox2/util/path.h"
#include "sandboxed_api/sandbox2/util/strerror.h"
#include "sandboxed_api/util/raw_logging.h"
namespace sandbox2 {
namespace util {
void CharPtrArrToVecString(char* const* arr, std::vector<std::string>* vec) {
for (int i = 0; arr[i]; ++i) {
vec->push_back(arr[i]);
}
}
const char** VecStringToCharPtrArr(const std::vector<std::string>& vec) {
const int vec_size = vec.size();
const char** arr = new const char*[vec_size + 1];
for (int i = 0; i < vec_size; ++i) {
arr[i] = vec[i].c_str();
}
arr[vec_size] = nullptr;
return arr;
}
std::string GetProgName(pid_t pid) {
std::string fname = file::JoinPath("/proc", absl::StrCat(pid), "exe");
// Use ReadLink instead of RealPath, as for fd-based executables (e.g. created
// via memfd_create()) the RealPath will not work, as the destination file
// doesn't exist on the local file-system.
return file_util::fileops::Basename(file_util::fileops::ReadLink(fname));
}
long Syscall(long sys_no, // NOLINT
uintptr_t a1, uintptr_t a2, uintptr_t a3, uintptr_t a4,
uintptr_t a5, uintptr_t a6) {
return syscall(sys_no, a1, a2, a3, a4, a5, a6);
}
bool CreateDirRecursive(const std::string& path, mode_t mode) {
int error = mkdir(path.c_str(), mode);
if (error == 0 || errno == EEXIST) {
return true;
}
// We couldn't create the dir for reasons we can't handle.
if (errno != ENOENT) {
return false;
}
// The EEXIST case, the parent directory doesn't exist yet.
// Let's create it.
const std::string dir = file_util::fileops::StripBasename(path);
if (dir == "/" || dir.empty()) {
return false;
}
if (!CreateDirRecursive(dir, mode)) {
return false;
}
// Now the parent dir exists, retry creating the directory.
error = mkdir(path.c_str(), mode);
return error == 0;
}
namespace {
int ChildFunc(void* arg) {
auto* env_ptr = reinterpret_cast<jmp_buf*>(arg);
// Restore the old stack.
longjmp(*env_ptr, 1);
}
// This code is inspired by base/process/launch_posix.cc in the Chromium source.
// There are a few things to be careful of here:
// - Make sure the stack_buf is below the env_ptr to please FORTIFY_SOURCE.
// - Make sure the stack_buf is not too far away from the real stack to please
// ASAN. If they are too far away, a warning is printed. This means not only
// that the temporary stack buffer needs to also be on the stack, but also that
// we need to disable ASAN for this function, to prevent it from being placed on
// the fake ASAN stack.
// - Make sure that the buffer is aligned to whatever is required by the CPU.
ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS
ABSL_ATTRIBUTE_NOINLINE
pid_t CloneAndJump(int flags, jmp_buf* env_ptr) {
uint8_t stack_buf[PTHREAD_STACK_MIN] ABSL_CACHELINE_ALIGNED;
#if defined(__x86_64__) || defined(__x86__) || defined(__i386__) || \
defined(__powerpc64__)
// Stack grows down.
void* stack = stack_buf + sizeof(stack_buf);
#else
#error "Architecture is not supported"
#endif
int r;
{
r = clone(&ChildFunc, stack, flags, env_ptr, nullptr, nullptr, nullptr);
}
if (r == -1) {
SAPI_RAW_PLOG(ERROR, "clone()");
}
return r;
}
} // namespace
pid_t ForkWithFlags(int flags) {
const int unsupported_flags = CLONE_CHILD_CLEARTID | CLONE_CHILD_SETTID |
CLONE_PARENT_SETTID | CLONE_SETTLS | CLONE_VM;
if (flags & unsupported_flags) {
SAPI_RAW_LOG(ERROR, "ForkWithFlags used with unsupported flag");
return -1;
}
jmp_buf env;
if (setjmp(env) == 0) {
return CloneAndJump(flags, &env);
}
// Child.
return 0;
}
bool CreateMemFd(int* fd, const char* name) {
// Usually defined in linux/memfd.h. Define it here to avoid dependency on
// UAPI headers.
constexpr uintptr_t MFD_CLOEXEC = 0x0001U;
int tmp_fd = Syscall(__NR_memfd_create, reinterpret_cast<uintptr_t>(name),
MFD_CLOEXEC);
if (tmp_fd < 0) {
if (errno == ENOSYS) {
SAPI_RAW_LOG(ERROR,
"This system does not seem to support the memfd_create()"
" syscall. Try running on a newer kernel.");
} else {
SAPI_RAW_PLOG(ERROR, "Could not create tmp file '%s'", name);
}
return false;
}
*fd = tmp_fd;
return true;
}
absl::StatusOr<int> Communicate(const std::vector<std::string>& argv,
const std::vector<std::string>& envv,
std::string* output) {
int cout_pipe[2];
posix_spawn_file_actions_t action;
if (pipe(cout_pipe) == -1) {
return absl::UnknownError(absl::StrCat("creating pipe: ", StrError(errno)));
}
file_util::fileops::FDCloser cout_closer{cout_pipe[1]};
posix_spawn_file_actions_init(&action);
struct ActionCleanup {
~ActionCleanup() { posix_spawn_file_actions_destroy(action_); }
posix_spawn_file_actions_t* action_;
} action_cleanup{&action};
// Redirect both stdout and stderr to stdout to our pipe.
posix_spawn_file_actions_addclose(&action, cout_pipe[0]);
posix_spawn_file_actions_adddup2(&action, cout_pipe[1], 1);
posix_spawn_file_actions_adddup2(&action, cout_pipe[1], 2);
posix_spawn_file_actions_addclose(&action, cout_pipe[1]);
char** args = const_cast<char**>(util::VecStringToCharPtrArr(argv));
char** envp = const_cast<char**>(util::VecStringToCharPtrArr(envv));
struct ArgumentCleanup {
~ArgumentCleanup() {
delete[] args_;
delete[] envp_;
}
char** args_;
char** envp_;
} args_cleanup{args, envp};
pid_t pid;
if (posix_spawnp(&pid, args[0], &action, nullptr, args, envp) != 0) {
return absl::UnknownError(
absl::StrCat("posix_spawnp() failed: ", StrError(errno)));
}
// Close child end of the pipe.
cout_closer.Close();
std::string buffer(1024, '\0');
for (;;) {
int bytes_read =
TEMP_FAILURE_RETRY(read(cout_pipe[0], &buffer[0], buffer.length()));
if (bytes_read < 0) {
return absl::InternalError(
absl::StrCat("reading from cout pipe failed: ", StrError(errno)));
}
if (bytes_read == 0) {
break; // Nothing left to read
}
absl::StrAppend(output, absl::string_view(buffer.data(), bytes_read));
}
int status;
SAPI_RAW_PCHECK(TEMP_FAILURE_RETRY(waitpid(pid, &status, 0)) == pid,
"Waiting for subprocess");
return WEXITSTATUS(status);
}
std::string GetSignalName(int signo) {
constexpr absl::string_view kSignalNames[] = {
"SIG_0", "SIGHUP", "SIGINT", "SIGQUIT", "SIGILL", "SIGTRAP",
"SIGABRT", "SIGBUS", "SIGFPE", "SIGKILL", "SIGUSR1", "SIGSEGV",
"SIGUSR2", "SIGPIPE", "SIGALRM", "SIGTERM", "SIGSTKFLT", "SIGCHLD",
"SIGCONT", "SIGSTOP", "SIGTSTP", "SIGTTIN", "SIGTTOU", "SIGURG",
"SIGXCPU", "SIGXFSZ", "SIGVTALARM", "SIGPROF", "SIGWINCH", "SIGIO",
"SIGPWR", "SIGSYS"};
if (signo >= SIGRTMIN && signo <= SIGRTMAX) {
return absl::StrFormat("SIGRT-%d [%d]", signo - SIGRTMIN, signo);
}
if (signo < 0 || signo >= static_cast<int>(ABSL_ARRAYSIZE(kSignalNames))) {
return absl::StrFormat("UNKNOWN_SIGNAL [%d]", signo);
}
return absl::StrFormat("%s [%d]", kSignalNames[signo], signo);
}
std::string GetRlimitName(int resource) {
switch (resource) {
case RLIMIT_AS:
return "RLIMIT_AS";
case RLIMIT_FSIZE:
return "RLIMIT_FSIZE";
case RLIMIT_NOFILE:
return "RLIMIT_NOFILE";
case RLIMIT_CPU:
return "RLIMIT_CPU";
case RLIMIT_CORE:
return "RLIMIT_CORE";
default:
return absl::StrCat("UNKNOWN: ", resource);
}
}
absl::StatusOr<std::string> ReadCPathFromPid(pid_t pid, uintptr_t ptr) {
std::string path(PATH_MAX, '\0');
iovec local_iov[] = {{&path[0], path.size()}};
static const uintptr_t page_size = getpagesize();
static const uintptr_t page_mask = ~(page_size - 1);
// See 'man process_vm_readv' for details on how to read NUL-terminated
// strings with this syscall.
size_t len1 = ((ptr + page_size) & page_mask) - ptr;
len1 = (len1 > path.size()) ? path.size() : len1;
size_t len2 = (path.size() <= len1) ? 0UL : path.size() - len1;
// Second iov is wrapping around to NULL ptr.
if ((ptr + len1) < ptr) {
len2 = 0UL;
}
iovec remote_iov[] = {
{reinterpret_cast<void*>(ptr), len1},
{reinterpret_cast<void*>(ptr + len1), len2},
};
SAPI_RAW_VLOG(4, "ReadCPathFromPid (iovec): len1: %d, len2: %d", len1, len2);
ssize_t sz = process_vm_readv(pid, local_iov, ABSL_ARRAYSIZE(local_iov),
remote_iov, ABSL_ARRAYSIZE(remote_iov), 0);
if (sz < 0) {
return absl::InternalError(absl::StrFormat(
"process_vm_readv() failed for PID: %d at address: %#x: %s", pid,
reinterpret_cast<uintptr_t>(ptr), StrError(errno)));
}
// Check for whether there's a NUL byte in the buffer. If not, it's an
// incorrect path (or >PATH_MAX).
auto pos = path.find('\0');
if (pos == std::string::npos) {
return absl::FailedPreconditionError(absl::StrCat(
"No NUL-byte inside the C string '", absl::CHexEscape(path), "'"));
}
path.resize(pos);
return path;
}
} // namespace util
} // namespace sandbox2