sandboxed-api/sandboxed_api/sandbox2/mounts.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.
#include "sandboxed_api/sandbox2/mounts.h"
#include <fcntl.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <sys/statvfs.h>
#include <sys/types.h>
#include <unistd.h>
#include <climits>
#include <memory>
#include <utility>
#include "google/protobuf/util/message_differencer.h"
#include "absl/container/flat_hash_set.h"
#include "absl/status/status.h"
#include "absl/status/statusor.h"
#include "absl/strings/ascii.h"
#include "absl/strings/match.h"
#include "absl/strings/str_cat.h"
#include "absl/strings/str_join.h"
#include "absl/strings/str_split.h"
#include "absl/strings/string_view.h"
#include "absl/strings/strip.h"
#include "sandboxed_api/config.h"
#include "sandboxed_api/sandbox2/util/minielf.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"
#include "sandboxed_api/util/strerror.h"
namespace sandbox2 {
namespace {
namespace cpu = ::sapi::cpu;
namespace file_util = ::sapi::file_util;
namespace host_cpu = ::sapi::host_cpu;
bool PathContainsNullByte(absl::string_view path) {
return absl::StrContains(path, '\0');
}
bool IsSameFile(const std::string& path1, const std::string& path2) {
struct stat stat1, stat2;
if (stat(path1.c_str(), &stat1) == -1) {
return false;
}
if (stat(path2.c_str(), &stat2) == -1) {
return false;
}
return stat1.st_dev == stat2.st_dev && stat1.st_ino == stat2.st_ino;
}
bool IsEquivalentNode(const sandbox2::MountTree::Node& n1,
const sandbox2::MountTree::Node& n2) {
// Node equals 1:1
if (google::protobuf::util::MessageDifferencer::Equals(n1, n2)) {
return true;
}
if (n1.node_case() != n2.node_case()) {
return false;
}
// Check whether files/dirs are the same (e.g symlinks / hardlinks)
switch (n1.node_case()) {
case sandbox2::MountTree::Node::kFileNode:
return n1.file_node().is_ro() == n2.file_node().is_ro() &&
IsSameFile(n1.file_node().outside(), n2.file_node().outside());
case sandbox2::MountTree::Node::kDirNode:
return n1.dir_node().is_ro() == n2.dir_node().is_ro() &&
IsSameFile(n1.dir_node().outside(), n2.dir_node().outside());
default:
return false;
}
}
absl::string_view GetOutsidePath(const MountTree::Node& node) {
switch (node.node_case()) {
case MountTree::Node::kFileNode:
return node.file_node().outside();
case MountTree::Node::kDirNode:
return node.dir_node().outside();
default:
SAPI_RAW_LOG(FATAL, "Invalid node type");
return ""; // NOT REACHED
}
}
absl::StatusOr<std::string> ExistingPathInsideDir(
absl::string_view dir_path, absl::string_view relative_path) {
auto path =
sapi::file::CleanPath(sapi::file::JoinPath(dir_path, relative_path));
if (file_util::fileops::StripBasename(path) != dir_path) {
return absl::InvalidArgumentError("Relative path goes above the base dir");
}
if (!file_util::fileops::Exists(path, false)) {
return absl::NotFoundError(absl::StrCat("Does not exist: ", path));
}
return path;
}
absl::Status ValidateInterpreter(absl::string_view interpreter) {
const absl::flat_hash_set<std::string> allowed_interpreters = {
"/lib64/ld-linux-x86-64.so.2",
"/lib64/ld64.so.2", // PPC64
"/lib/ld-linux-aarch64.so.1", // AArch64
"/lib/ld-linux-armhf.so.3", // Arm
};
if (!allowed_interpreters.contains(interpreter)) {
return absl::InvalidArgumentError(
absl::StrCat("Interpreter not on the whitelist: ", interpreter));
}
return absl::OkStatus();
}
std::string ResolveLibraryPath(absl::string_view lib_name,
const std::vector<std::string>& search_paths) {
for (const auto& search_path : search_paths) {
if (auto path_or = ExistingPathInsideDir(search_path, lib_name);
path_or.ok()) {
return path_or.value();
}
}
return "";
}
constexpr absl::string_view GetPlatformCPUName() {
switch (host_cpu::Architecture()) {
case cpu::kX8664:
return "x86_64";
case cpu::kPPC64LE:
return "ppc64";
case cpu::kArm64:
return "aarch64";
default:
return "unknown";
}
}
std::string GetPlatform(absl::string_view interpreter) {
return absl::StrCat(GetPlatformCPUName(), "-linux-gnu");
}
} // namespace
absl::Status Mounts::Insert(absl::string_view path,
const MountTree::Node& new_node) {
// Some sandboxes allow the inside/outside paths to be partially
// user-controlled with some sanitization.
// Since we're handling C++ strings and later convert them to C style
// strings, a null byte in a path component might silently truncate the path
// and mount something not expected by the caller. Check for null bytes in the
// strings to protect against this.
if (PathContainsNullByte(path)) {
return absl::InvalidArgumentError(
absl::StrCat("Inside path contains a null byte: ", path));
}
switch (new_node.node_case()) {
case MountTree::Node::kFileNode:
case MountTree::Node::kDirNode: {
auto outside_path = GetOutsidePath(new_node);
if (outside_path.empty()) {
return absl::InvalidArgumentError("Outside path cannot be empty");
}
if (PathContainsNullByte(outside_path)) {
return absl::InvalidArgumentError(
absl::StrCat("Outside path contains a null byte: ", outside_path));
}
break;
}
case MountTree::Node::kRootNode:
return absl::InvalidArgumentError("Cannot insert a RootNode");
case MountTree::Node::kTmpfsNode:
case MountTree::Node::NODE_NOT_SET:
break;
}
std::string fixed_path = sapi::file::CleanPath(path);
if (!sapi::file::IsAbsolutePath(fixed_path)) {
return absl::InvalidArgumentError("Only absolute paths are supported");
}
if (fixed_path == "/") {
return absl::InvalidArgumentError("The root already exists");
}
std::vector<absl::string_view> parts =
absl::StrSplit(absl::StripPrefix(fixed_path, "/"), '/');
std::string final_part(parts.back());
parts.pop_back();
MountTree* curtree = &mount_tree_;
for (absl::string_view part : parts) {
curtree = &(curtree->mutable_entries()
->insert({std::string(part), MountTree()})
.first->second);
if (curtree->has_node() && curtree->node().has_file_node()) {
return absl::FailedPreconditionError(
absl::StrCat("Cannot insert ", path,
" since a file is mounted as a parent directory"));
}
}
curtree = &(curtree->mutable_entries()
->insert({final_part, MountTree()})
.first->second);
if (curtree->has_node()) {
if (IsEquivalentNode(curtree->node(), new_node)) {
SAPI_RAW_LOG(INFO, "Inserting %s with the same value twice",
std::string(path).c_str());
return absl::OkStatus();
}
return absl::FailedPreconditionError(absl::StrCat(
"Inserting ", path, " twice with conflicting values ",
curtree->node().DebugString(), " vs. ", new_node.DebugString()));
}
if (new_node.has_file_node() && !curtree->entries().empty()) {
return absl::FailedPreconditionError(
absl::StrCat("Trying to mount file over existing directory at ", path));
}
*curtree->mutable_node() = new_node;
return absl::OkStatus();
}
absl::Status Mounts::AddFile(absl::string_view path, bool is_ro) {
return AddFileAt(path, path, is_ro);
}
absl::Status Mounts::AddFileAt(absl::string_view outside,
absl::string_view inside, bool is_ro) {
MountTree::Node node;
auto* file_node = node.mutable_file_node();
file_node->set_outside(std::string(outside));
file_node->set_is_ro(is_ro);
return Insert(inside, node);
}
absl::Status Mounts::AddDirectoryAt(absl::string_view outside,
absl::string_view inside, bool is_ro) {
MountTree::Node node;
auto dir_node = node.mutable_dir_node();
dir_node->set_outside(std::string(outside));
dir_node->set_is_ro(is_ro);
return Insert(inside, node);
}
absl::StatusOr<std::string> Mounts::ResolvePath(absl::string_view path) const {
if (!sapi::file::IsAbsolutePath(path)) {
return absl::InvalidArgumentError("Path has to be absolute");
}
std::string fixed_path = sapi::file::CleanPath(path);
absl::string_view tail = absl::StripPrefix(fixed_path, "/");
const MountTree* curtree = &mount_tree_;
while (!tail.empty()) {
std::pair<absl::string_view, absl::string_view> parts =
absl::StrSplit(tail, absl::MaxSplits('/', 1));
const std::string cur(parts.first);
const auto it = curtree->entries().find(cur);
if (it == curtree->entries().end()) {
if (curtree->node().has_dir_node()) {
return sapi::file::JoinPath(curtree->node().dir_node().outside(), tail);
}
return absl::NotFoundError("Path could not be resolved in the mounts");
}
curtree = &it->second;
tail = parts.second;
}
switch (curtree->node().node_case()) {
case MountTree::Node::kFileNode:
case MountTree::Node::kDirNode:
return std::string(GetOutsidePath(curtree->node()));
case MountTree::Node::kRootNode:
case MountTree::Node::kTmpfsNode:
case MountTree::Node::NODE_NOT_SET:
break;
}
return absl::NotFoundError("Path could not be resolved in the mounts");
}
namespace {
void LogContainer(const std::vector<std::string>& container) {
for (size_t i = 0; i < container.size(); ++i) {
SAPI_RAW_LOG(INFO, "[%4zd]=%s", i, container[i].c_str());
}
}
} // namespace
absl::Status Mounts::AddMappingsForBinary(const std::string& path,
absl::string_view ld_library_path) {
SAPI_ASSIGN_OR_RETURN(
auto elf,
ElfFile::ParseFromFile(
path, ElfFile::kGetInterpreter | ElfFile::kLoadImportedLibraries));
const std::string& interpreter = elf.interpreter();
if (interpreter.empty()) {
SAPI_RAW_VLOG(1, "The file %s is not a dynamic executable", path.c_str());
return absl::OkStatus();
}
SAPI_RAW_VLOG(1, "The file %s is using interpreter %s", path.c_str(),
interpreter.c_str());
SAPI_RETURN_IF_ERROR(ValidateInterpreter(interpreter));
std::vector<std::string> search_paths;
// 1. LD_LIBRARY_PATH
if (!ld_library_path.empty()) {
std::vector<std::string> ld_library_paths =
absl::StrSplit(ld_library_path, absl::ByAnyChar(":;"));
search_paths.insert(search_paths.end(), ld_library_paths.begin(),
ld_library_paths.end());
}
// 2. Standard paths
search_paths.insert(search_paths.end(), {
"/lib",
"/lib64",
"/usr/lib",
"/usr/lib64",
});
std::vector<std::string> hw_cap_paths = {
GetPlatform(interpreter),
"tls",
};
std::vector<std::string> full_search_paths;
for (const auto& search_path : search_paths) {
for (int hw_caps_set = (1 << hw_cap_paths.size()) - 1; hw_caps_set >= 0;
--hw_caps_set) {
std::string path = search_path;
for (int hw_cap = 0; hw_cap < hw_cap_paths.size(); ++hw_cap) {
if ((hw_caps_set & (1 << hw_cap)) != 0) {
path = sapi::file::JoinPath(path, hw_cap_paths[hw_cap]);
}
}
if (file_util::fileops::Exists(path, /*fully_resolve=*/false)) {
full_search_paths.push_back(path);
}
}
}
// Arbitrary cut-off values, so we can safely resolve the libs.
constexpr int kMaxWorkQueueSize = 1000;
constexpr int kMaxResolvingDepth = 10;
constexpr int kMaxResolvedEntries = 1000;
constexpr int kMaxLoadedEntries = 100;
constexpr int kMaxImportedLibraries = 100;
absl::flat_hash_set<std::string> imported_libraries;
std::vector<std::pair<std::string, int>> to_resolve;
{
auto imported_libs = elf.imported_libraries();
if (imported_libs.size() > kMaxWorkQueueSize) {
return absl::FailedPreconditionError(
"Exceeded max entries pending resolving limit");
}
for (const auto& imported_lib : imported_libs) {
to_resolve.emplace_back(imported_lib, 1);
}
if (SAPI_VLOG_IS_ON(1)) {
SAPI_RAW_VLOG(
1, "Resolving dynamic library dependencies of %s using these dirs:",
path.c_str());
LogContainer(full_search_paths);
}
if (SAPI_VLOG_IS_ON(2)) {
SAPI_RAW_VLOG(2, "Direct dependencies of %s to resolve:", path.c_str());
LogContainer(imported_libs);
}
}
// This is DFS with an auxiliary stack
int resolved = 0;
int loaded = 0;
while (!to_resolve.empty()) {
int depth;
std::string lib;
std::tie(lib, depth) = to_resolve.back();
to_resolve.pop_back();
++resolved;
if (resolved > kMaxResolvedEntries) {
return absl::FailedPreconditionError(
"Exceeded max resolved entries limit");
}
if (depth > kMaxResolvingDepth) {
return absl::FailedPreconditionError(
"Exceeded max resolving depth limit");
}
std::string resolved_lib = ResolveLibraryPath(lib, full_search_paths);
if (resolved_lib.empty()) {
SAPI_RAW_LOG(ERROR, "Failed to resolve library: %s", lib.c_str());
continue;
}
if (imported_libraries.contains(resolved_lib)) {
continue;
}
SAPI_RAW_VLOG(1, "Resolved library: %s => %s", lib.c_str(),
resolved_lib.c_str());
imported_libraries.insert(resolved_lib);
if (imported_libraries.size() > kMaxImportedLibraries) {
return absl::FailedPreconditionError(
"Exceeded max imported libraries limit");
}
++loaded;
if (loaded > kMaxLoadedEntries) {
return absl::FailedPreconditionError("Exceeded max loaded entries limit");
}
SAPI_ASSIGN_OR_RETURN(
auto lib_elf,
ElfFile::ParseFromFile(resolved_lib, ElfFile::kLoadImportedLibraries));
auto imported_libs = lib_elf.imported_libraries();
if (imported_libs.size() > kMaxWorkQueueSize - to_resolve.size()) {
return absl::FailedPreconditionError(
"Exceeded max entries pending resolving limit");
}
if (SAPI_VLOG_IS_ON(2)) {
SAPI_RAW_VLOG(2,
"Transitive dependencies of %s to resolve (depth = %d): ",
resolved_lib.c_str(), depth + 1);
LogContainer(imported_libs);
}
for (const auto& imported_lib : imported_libs) {
to_resolve.emplace_back(imported_lib, depth + 1);
}
}
imported_libraries.insert(interpreter);
for (const auto& lib : imported_libraries) {
SAPI_RETURN_IF_ERROR(AddFile(lib));
}
return absl::OkStatus();
}
absl::Status Mounts::AddTmpfs(absl::string_view inside, size_t sz) {
MountTree::Node node;
auto tmpfs_node = node.mutable_tmpfs_node();
tmpfs_node->set_tmpfs_options(absl::StrCat("size=", sz));
return Insert(inside, node);
}
namespace {
uint64_t GetMountFlagsFor(const std::string& path) {
struct statvfs vfs;
if (TEMP_FAILURE_RETRY(statvfs(path.c_str(), &vfs)) == -1) {
SAPI_RAW_PLOG(ERROR, "statvfs");
return 0;
}
uint64_t flags = 0;
using MountPair = std::pair<uint64_t, uint64_t>;
for (const auto& [mount_flag, vfs_flag] : {
MountPair(MS_NOSUID, ST_NOSUID),
MountPair(MS_NODEV, ST_NODEV),
MountPair(MS_NOEXEC, ST_NOEXEC),
MountPair(MS_SYNCHRONOUS, ST_SYNCHRONOUS),
MountPair(MS_MANDLOCK, ST_MANDLOCK),
MountPair(MS_NOATIME, ST_NOATIME),
MountPair(MS_NODIRATIME, ST_NODIRATIME),
MountPair(MS_RELATIME, ST_RELATIME),
}) {
if (vfs.f_flag & vfs_flag) {
flags |= mount_flag;
}
}
return flags;
}
std::string MountFlagsToString(uint64_t flags) {
#define SAPI_MAP(x) \
{ x, #x }
static constexpr std::pair<uint64_t, absl::string_view> kMap[] = {
SAPI_MAP(MS_RDONLY), SAPI_MAP(MS_NOSUID),
SAPI_MAP(MS_NODEV), SAPI_MAP(MS_NOEXEC),
SAPI_MAP(MS_SYNCHRONOUS), SAPI_MAP(MS_REMOUNT),
SAPI_MAP(MS_MANDLOCK), SAPI_MAP(MS_DIRSYNC),
SAPI_MAP(MS_NOATIME), SAPI_MAP(MS_NODIRATIME),
SAPI_MAP(MS_BIND), SAPI_MAP(MS_MOVE),
SAPI_MAP(MS_REC),
#ifdef MS_VERBOSE
SAPI_MAP(MS_VERBOSE), // Deprecated
#endif
SAPI_MAP(MS_SILENT), SAPI_MAP(MS_POSIXACL),
SAPI_MAP(MS_UNBINDABLE), SAPI_MAP(MS_PRIVATE),
SAPI_MAP(MS_SLAVE), // Inclusive language: system constant
SAPI_MAP(MS_SHARED), SAPI_MAP(MS_RELATIME),
SAPI_MAP(MS_KERNMOUNT), SAPI_MAP(MS_I_VERSION),
SAPI_MAP(MS_STRICTATIME),
#ifdef MS_LAZYTIME
SAPI_MAP(MS_LAZYTIME), // Added in Linux 4.0
#endif
};
#undef SAPI_MAP
std::vector<absl::string_view> flags_list;
for (const auto& [val, str] : kMap) {
if ((flags & val) == val) {
flags &= ~val;
flags_list.push_back(str);
}
}
std::string flags_str = absl::StrCat(flags);
if (flags_list.empty() || flags != 0) {
flags_list.push_back(flags_str);
}
return absl::StrJoin(flags_list, "|");
}
void MountWithDefaults(const std::string& source, const std::string& target,
const char* fs_type, uint64_t extra_flags,
const char* option_str, bool is_ro) {
uint64_t flags = MS_REC | MS_NOSUID | extra_flags;
if (is_ro) {
flags |= MS_RDONLY;
}
SAPI_RAW_VLOG(1, R"(mount("%s", "%s", "%s", %s, "%s"))", source.c_str(),
target.c_str(), fs_type, MountFlagsToString(flags).c_str(),
option_str);
int res = mount(source.c_str(), target.c_str(), fs_type, flags, option_str);
if (res == -1) {
if (errno == ENOENT) {
// File does not exist (anymore). This is e.g. the case when we're trying
// to gather stack-traces on SAPI crashes. The sandboxee application is a
// memfd file that is not existing anymore.
SAPI_RAW_LOG(WARNING, "Could not mount %s: file does not exist",
source.c_str());
return;
}
SAPI_RAW_PLOG(FATAL, "mounting %s to %s failed (flags=%s)", source, target,
MountFlagsToString(flags));
}
// Flags are ignored for a bind mount, a remount is needed to set the flags.
if (extra_flags & MS_BIND) {
// Get actual mount flags.
flags |= GetMountFlagsFor(target);
res = mount("", target.c_str(), "", flags | MS_REMOUNT, nullptr);
SAPI_RAW_PCHECK(res != -1, "remounting %s with flags=%s failed", target,
MountFlagsToString(flags));
}
// Mount propagation has to be set separately
const uint64_t propagation =
extra_flags & (MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE);
if (propagation != 0) {
res = mount("", target.c_str(), "", propagation, nullptr);
SAPI_RAW_PCHECK(res != -1, "changing %s mount propagation to %s failed",
target, MountFlagsToString(propagation).c_str());
}
}
// Traverses the MountTree to create all required files and perform the mounts.
void CreateMounts(const MountTree& tree, const std::string& path,
bool create_backing_files) {
// First, create the backing files if needed.
if (create_backing_files) {
switch (tree.node().node_case()) {
case MountTree::Node::kFileNode: {
SAPI_RAW_VLOG(2, "Creating backing file at %s", path.c_str());
int fd = open(path.c_str(), O_CREAT | O_EXCL | O_WRONLY, 0600);
SAPI_RAW_PCHECK(fd != -1, "");
SAPI_RAW_PCHECK(close(fd) == 0, "");
break;
}
case MountTree::Node::kDirNode:
case MountTree::Node::kTmpfsNode:
case MountTree::Node::kRootNode:
case MountTree::Node::NODE_NOT_SET:
SAPI_RAW_VLOG(2, "Creating directory at %s", path.c_str());
SAPI_RAW_PCHECK(mkdir(path.c_str(), 0700) == 0 || errno == EEXIST, "");
break;
// Intentionally no default to make sure we handle all the cases.
}
}
// Perform the actual mounts based on the node type.
switch (tree.node().node_case()) {
case MountTree::Node::kDirNode: {
// Since this directory is bind mounted, it's the users
// responsibility to make sure that all backing files are in place.
create_backing_files = false;
auto node = tree.node().dir_node();
MountWithDefaults(node.outside(), path, "", MS_BIND, nullptr,
node.is_ro());
break;
}
case MountTree::Node::kTmpfsNode: {
// We can always create backing files under a tmpfs.
create_backing_files = true;
auto node = tree.node().tmpfs_node();
MountWithDefaults("", path, "tmpfs", 0, node.tmpfs_options().c_str(),
/* is_ro */ false);
break;
}
case MountTree::Node::kFileNode: {
auto node = tree.node().file_node();
MountWithDefaults(node.outside(), path, "", MS_BIND, nullptr,
node.is_ro());
// A file node has to be a leaf so we can skip traversing here.
return;
}
case MountTree::Node::kRootNode:
case MountTree::Node::NODE_NOT_SET:
// Nothing to do, we already created the directory above.
break;
// Intentionally no default to make sure we handle all the cases.
}
// Traverse the subtrees.
for (const auto& kv : tree.entries()) {
std::string new_path = sapi::file::JoinPath(path, kv.first);
CreateMounts(kv.second, new_path, create_backing_files);
}
}
} // namespace
void Mounts::CreateMounts(const std::string& root_path) const {
sandbox2::CreateMounts(mount_tree_, root_path, true);
}
namespace {
void RecursivelyListMountsImpl(const MountTree& tree,
const std::string& tree_path,
std::vector<std::string>* outside_entries,
std::vector<std::string>* inside_entries) {
const MountTree::Node& node = tree.node();
if (node.has_dir_node()) {
const char* rw_str = node.dir_node().is_ro() ? "R " : "W ";
inside_entries->emplace_back(absl::StrCat(rw_str, tree_path, "/"));
outside_entries->emplace_back(absl::StrCat(node.dir_node().outside(), "/"));
} else if (node.has_file_node()) {
const char* rw_str = node.file_node().is_ro() ? "R " : "W ";
inside_entries->emplace_back(absl::StrCat(rw_str, tree_path));
outside_entries->emplace_back(absl::StrCat(node.file_node().outside()));
} else if (node.has_tmpfs_node()) {
inside_entries->emplace_back(tree_path);
outside_entries->emplace_back(
absl::StrCat("tmpfs: ", node.tmpfs_node().tmpfs_options()));
}
for (const auto& subentry : tree.entries()) {
RecursivelyListMountsImpl(subentry.second,
absl::StrCat(tree_path, "/", subentry.first),
outside_entries, inside_entries);
}
}
} // namespace
void Mounts::RecursivelyListMounts(std::vector<std::string>* outside_entries,
std::vector<std::string>* inside_entries) {
RecursivelyListMountsImpl(GetMountTree(), "", outside_entries,
inside_entries);
}
} // namespace sandbox2