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sandboxed-api/sandboxed_api/sandbox2/namespace.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 file for the sandbox2::Namespace class.
#include "sandboxed_api/sandbox2/namespace.h"
#include <fcntl.h>
#include <net/if.h>
#include <sched.h>
#include <sys/ioctl.h>
#include <sys/mount.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <syscall.h>
#include <unistd.h>
#include <cstdint>
#include <cstring>
#include <memory>
#include <string>
#include <utility>
#include <vector>
#include "absl/strings/str_cat.h"
#include "sandboxed_api/sandbox2/violation.pb.h"
#include "sandboxed_api/util/fileops.h"
#include "sandboxed_api/util/path.h"
#include "sandboxed_api/util/raw_logging.h"
namespace sandbox2 {
namespace file = ::sapi::file;
namespace file_util = ::sapi::file_util;
static constexpr char kSandbox2ChrootPath[] = "/tmp/.sandbox2chroot";
namespace {
int MountFallbackToReadOnly(const char* source, const char* target,
const char* filesystem, uintptr_t flags,
const void* data) {
int rv = mount(source, target, filesystem, flags, data);
if (rv != 0 && (flags & MS_RDONLY) == 0) {
SAPI_RAW_PLOG(WARNING, "Mounting %s on %s (fs type %s) read-write failed",
source, target, filesystem);
rv = mount(source, target, filesystem, flags | MS_RDONLY, data);
if (rv == 0) {
SAPI_RAW_LOG(INFO, "Mounted %s on %s (fs type %s) as read-only", source,
target, filesystem);
}
}
return rv;
}
void PrepareChroot(const Mounts& mounts) {
// Create a tmpfs mount for the new rootfs.
SAPI_RAW_CHECK(
file_util::fileops::CreateDirectoryRecursively(kSandbox2ChrootPath, 0700),
"could not create directory for rootfs");
SAPI_RAW_PCHECK(mount("none", kSandbox2ChrootPath, "tmpfs", 0, nullptr) == 0,
"mounting rootfs failed");
// Walk the tree and perform all the mount operations.
mounts.CreateMounts(kSandbox2ChrootPath);
if (mounts.IsRootReadOnly()) {
// Remount the chroot read-only
SAPI_RAW_PCHECK(mount(kSandbox2ChrootPath, kSandbox2ChrootPath, "",
MS_BIND | MS_REMOUNT | MS_RDONLY, nullptr) == 0,
"remounting chroot read-only failed");
}
}
void TryDenySetgroups() {
file_util::fileops::FDCloser fd(
TEMP_FAILURE_RETRY(open("/proc/self/setgroups", O_WRONLY | O_CLOEXEC)));
// We ignore errors since they are most likely due to an old kernel.
if (fd.get() == -1) {
return;
}
dprintf(fd.get(), "deny");
}
void WriteIDMap(const char* map_path, int32_t uid) {
file_util::fileops::FDCloser fd(
TEMP_FAILURE_RETRY(open(map_path, O_WRONLY | O_CLOEXEC)));
SAPI_RAW_PCHECK(fd.get() != -1, "Couldn't open %s", map_path);
SAPI_RAW_PCHECK(dprintf(fd.get(), "1000 %d 1", uid) >= 0,
"Could not write %d to %s", uid, map_path);
}
void SetupIDMaps(uid_t uid, gid_t gid) {
TryDenySetgroups();
WriteIDMap("/proc/self/uid_map", uid);
WriteIDMap("/proc/self/gid_map", gid);
}
void ActivateLoopbackInterface() {
ifreq ifreq;
ifreq.ifr_flags = 0;
strncpy(ifreq.ifr_name, "lo", IFNAMSIZ);
// Create an AF_INET6 socket to perform the IF FLAGS ioctls on.
int fd = socket(AF_INET6, SOCK_DGRAM, 0);
SAPI_RAW_PCHECK(fd != -1, "creating socket for activating loopback failed");
file_util::fileops::FDCloser fd_closer{fd};
// First get the existing flags.
SAPI_RAW_PCHECK(ioctl(fd, SIOCGIFFLAGS, &ifreq) != -1,
"Getting existing flags");
// From 812 kernels, we don't have CAP_NET_ADMIN anymore. But the interface is
// already up, so we can skip the next ioctl.
if (ifreq.ifr_flags & IFF_UP) {
return;
}
// Set the UP flag and write the flags back.
ifreq.ifr_flags |= IFF_UP;
SAPI_RAW_PCHECK(ioctl(fd, SIOCSIFFLAGS, &ifreq) != -1, "Setting IFF_UP flag");
}
// Logs the filesystem contents if verbose logging is enabled.
void LogFilesystem(const std::string& dir) {
std::vector<std::string> entries;
std::string error;
if (!file_util::fileops::ListDirectoryEntries(dir, &entries, &error)) {
SAPI_RAW_PLOG(ERROR, "could not list directory entries for %s", dir);
return;
}
for (const auto& entry : entries) {
struct stat64 st;
std::string full_path = file::JoinPath(dir, entry);
if (lstat64(full_path.c_str(), &st) != 0) {
SAPI_RAW_PLOG(ERROR, "could not stat %s", full_path);
continue;
}
char ftype;
switch (st.st_mode & S_IFMT) {
case S_IFREG:
ftype = '-';
break;
case S_IFDIR:
ftype = 'd';
break;
case S_IFLNK:
ftype = 'l';
break;
default:
ftype = '?';
break;
}
std::string type_and_mode;
type_and_mode += ftype;
type_and_mode += st.st_mode & S_IRUSR ? 'r' : '-';
type_and_mode += st.st_mode & S_IWUSR ? 'w' : '-';
type_and_mode += st.st_mode & S_IXUSR ? 'x' : '-';
type_and_mode += st.st_mode & S_IRGRP ? 'r' : '-';
type_and_mode += st.st_mode & S_IWGRP ? 'w' : '-';
type_and_mode += st.st_mode & S_IXGRP ? 'x' : '-';
type_and_mode += st.st_mode & S_IROTH ? 'r' : '-';
type_and_mode += st.st_mode & S_IWOTH ? 'w' : '-';
type_and_mode += st.st_mode & S_IXOTH ? 'x' : '-';
std::string link;
if (S_ISLNK(st.st_mode)) {
link = absl::StrCat(" -> ", file_util::fileops::ReadLink(full_path));
}
SAPI_RAW_VLOG(2, "%s %s%s", type_and_mode.c_str(), full_path.c_str(),
link.c_str());
if (S_ISDIR(st.st_mode)) {
LogFilesystem(full_path);
}
}
}
} // namespace
Namespace::Namespace(bool allow_unrestricted_networking, Mounts mounts,
std::string hostname, bool allow_mount_propagation)
: mounts_(std::move(mounts)),
hostname_(std::move(hostname)),
allow_mount_propagation_(allow_mount_propagation) {
if (allow_unrestricted_networking) {
clone_flags_ &= ~CLONE_NEWNET;
}
}
void Namespace::InitializeNamespaces(uid_t uid, gid_t gid, int32_t clone_flags,
const Mounts& mounts,
const std::string& hostname,
bool avoid_pivot_root,
bool allow_mount_propagation) {
if (clone_flags & CLONE_NEWUSER && !avoid_pivot_root) {
SetupIDMaps(uid, gid);
}
if (!(clone_flags & CLONE_NEWNS)) {
// CLONE_NEWNS is always set if we're running in namespaces.
return;
}
std::unique_ptr<file_util::fileops::FDCloser> root_fd;
if (avoid_pivot_root) {
// We want to bind-mount chrooted to real root, so that symlinks work.
// Reference to main root is kept to escape later from the chroot
root_fd = std::make_unique<file_util::fileops::FDCloser>(
TEMP_FAILURE_RETRY(open("/", O_PATH)));
SAPI_RAW_CHECK(root_fd->get() != -1, "creating fd for main root");
SAPI_RAW_PCHECK(chroot("/realroot") != -1, "chrooting to real root");
SAPI_RAW_PCHECK(chdir("/") != -1, "chdir / after chrooting real root");
}
SAPI_RAW_PCHECK(mount("", "/proc", "proc", MS_NODEV | MS_NOEXEC | MS_NOSUID,
nullptr) != -1,
"Could not mount a new /proc"
);
if (clone_flags & CLONE_NEWNET) {
// Some things can only be done if inside a new network namespace, like
// mounting /sys, setting a hostname or bringing up lo if necessary.
SAPI_RAW_PCHECK(
MountFallbackToReadOnly("", "/sys", "sysfs",
MS_NODEV | MS_NOEXEC | MS_NOSUID,
nullptr) != -1,
"Could not mount a new /sys"
);
SAPI_RAW_PCHECK(sethostname(hostname.c_str(), hostname.size()) != -1,
"Could not set network namespace hostname '%s'", hostname);
ActivateLoopbackInterface();
}
PrepareChroot(mounts);
if (avoid_pivot_root) {
// Keep a reference to /proc/self as it might not be mounted later
file_util::fileops::FDCloser proc_self_fd(
TEMP_FAILURE_RETRY(open("/proc/self/", O_PATH)));
SAPI_RAW_PCHECK(proc_self_fd.get() != -1, "opening /proc/self");
// Return to the main root
SAPI_RAW_PCHECK(fchdir(root_fd->get()) != -1, "chdir to main root");
SAPI_RAW_PCHECK(chroot(".") != -1, "chrooting to main root");
SAPI_RAW_PCHECK(chdir("/") != -1, "chdir / after chrooting main root");
// Get a refrence to /realroot to umount it later
file_util::fileops::FDCloser realroot_fd(
TEMP_FAILURE_RETRY(open("/realroot", O_PATH)));
// Move the chroot out of realroot to /
std::string chroot_path = file::JoinPath("/realroot", kSandbox2ChrootPath);
SAPI_RAW_PCHECK(chdir(chroot_path.c_str()) != -1, "chdir to chroot");
SAPI_RAW_PCHECK(mount(".", "/", "", MS_MOVE, nullptr) == 0,
"moving rootfs failed");
SAPI_RAW_PCHECK(chroot(".") != -1, "chrooting moved chroot");
SAPI_RAW_PCHECK(chdir("/") != -1, "chdir / after chroot");
// Umount the realroot so that no reference is left
SAPI_RAW_PCHECK(fchdir(realroot_fd.get()) != -1, "fchdir to /realroot");
SAPI_RAW_PCHECK(umount2(".", MNT_DETACH) != -1, "detaching old root");
if (clone_flags & CLONE_NEWUSER) {
// Also CLONE_NEWNS so that / mount becomes locked
SAPI_RAW_PCHECK(unshare(CLONE_NEWUSER | CLONE_NEWNS) != -1,
"unshare(CLONE_NEWUSER | CLONE_NEWNS)");
// Setup ID maps using reference to /proc/self obatined earlier
file_util::fileops::FDCloser setgroups_fd(TEMP_FAILURE_RETRY(
openat(proc_self_fd.get(), "setgroups", O_WRONLY | O_CLOEXEC)));
// We ignore errors since they are most likely due to an old kernel.
if (setgroups_fd.get() != -1) {
dprintf(setgroups_fd.get(), "deny");
}
file_util::fileops::FDCloser uid_map_fd(
TEMP_FAILURE_RETRY(openat(proc_self_fd.get(), "uid_map", O_WRONLY)));
SAPI_RAW_PCHECK(uid_map_fd.get() != -1, "Couldn't open uid_map");
SAPI_RAW_PCHECK(dprintf(uid_map_fd.get(), "1000 1000 1") >= 0,
"Could not write uid_map");
file_util::fileops::FDCloser gid_map_fd(
TEMP_FAILURE_RETRY(openat(proc_self_fd.get(), "gid_map", O_WRONLY)));
SAPI_RAW_PCHECK(gid_map_fd.get() != -1, "Couldn't open gid_map");
SAPI_RAW_PCHECK(dprintf(gid_map_fd.get(), "1000 1000 1") >= 0,
"Could not write gid_map");
}
} else {
// This requires some explanation: It's actually possible to pivot_root('/',
// '/'). After this operation has been completed, the old root is mounted
// over the new root, and it's OK to simply umount('/') now, and to have
// new_root as '/'. This allows us not care about providing any special
// directory for old_root, which is sometimes not easy, given that e.g. /tmp
// might not always be present inside new_root.
SAPI_RAW_PCHECK(syscall(__NR_pivot_root, kSandbox2ChrootPath,
kSandbox2ChrootPath) != -1,
"pivot root");
SAPI_RAW_PCHECK(umount2("/", MNT_DETACH) != -1, "detaching old root");
}
SAPI_RAW_PCHECK(chdir("/") == 0,
"changing cwd after mntns initialization failed");
if (allow_mount_propagation) {
SAPI_RAW_PCHECK(mount("/", "/", "", MS_SLAVE | MS_REC, nullptr) == 0,
"changing mount propagation to slave failed");
} else {
SAPI_RAW_PCHECK(mount("/", "/", "", MS_PRIVATE | MS_REC, nullptr) == 0,
"changing mount propagation to private failed");
}
if (SAPI_RAW_VLOG_IS_ON(2)) {
SAPI_RAW_VLOG(2, "Dumping the sandboxee's filesystem:");
LogFilesystem("/");
}
}
void Namespace::InitializeInitialNamespaces(uid_t uid, gid_t gid) {
SetupIDMaps(uid, gid);
SAPI_RAW_CHECK(
file_util::fileops::CreateDirectoryRecursively(kSandbox2ChrootPath, 0700),
"could not create directory for rootfs");
SAPI_RAW_PCHECK(mount("none", kSandbox2ChrootPath, "tmpfs", 0, nullptr) == 0,
"mounting rootfs failed");
auto realroot_path = file::JoinPath(kSandbox2ChrootPath, "/realroot");
SAPI_RAW_CHECK(
file_util::fileops::CreateDirectoryRecursively(realroot_path, 0700),
"could not create directory for real root");
SAPI_RAW_PCHECK(syscall(__NR_pivot_root, kSandbox2ChrootPath,
realroot_path.c_str()) != -1,
"pivot root");
SAPI_RAW_PCHECK(symlink("/realroot/proc", "/proc") != -1, "symlinking /proc");
SAPI_RAW_PCHECK(
mount("/", "/", "", MS_BIND | MS_REMOUNT | MS_RDONLY, nullptr) == 0,
"remounting rootfs read-only failed");
}
void Namespace::GetNamespaceDescription(
NamespaceDescription* pb_description) const {
pb_description->set_clone_flags(clone_flags_);
*pb_description->mutable_mount_tree_mounts() = mounts_.GetMountTree();
}
} // namespace sandbox2
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