248 lines
8.2 KiB
C++
248 lines
8.2 KiB
C++
/*
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* Copyright (C) 2019 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include "mount_namespace.h"
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#include <sys/mount.h>
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#include <string>
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#include <vector>
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#include <ApexProperties.sysprop.h>
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#include <android-base/file.h>
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#include <android-base/logging.h>
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#include <android-base/properties.h>
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#include <android-base/result.h>
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#include <android-base/unique_fd.h>
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#include "util.h"
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namespace android {
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namespace init {
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namespace {
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static bool MakeShared(const std::string& mount_point, bool recursive = false) {
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unsigned long mountflags = MS_SHARED;
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if (recursive) {
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mountflags |= MS_REC;
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}
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if (mount(nullptr, mount_point.c_str(), nullptr, mountflags, nullptr) == -1) {
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PLOG(ERROR) << "Failed to change propagation type to shared";
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return false;
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}
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return true;
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}
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static bool MakePrivate(const std::string& mount_point, bool recursive = false) {
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unsigned long mountflags = MS_PRIVATE;
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if (recursive) {
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mountflags |= MS_REC;
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}
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if (mount(nullptr, mount_point.c_str(), nullptr, mountflags, nullptr) == -1) {
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PLOG(ERROR) << "Failed to change propagation type to private";
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return false;
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}
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return true;
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}
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static int OpenMountNamespace() {
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int fd = open("/proc/self/ns/mnt", O_RDONLY | O_CLOEXEC);
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if (fd < 0) {
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PLOG(ERROR) << "Cannot open fd for current mount namespace";
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}
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return fd;
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}
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static std::string GetMountNamespaceId() {
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std::string ret;
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if (!android::base::Readlink("/proc/self/ns/mnt", &ret)) {
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PLOG(ERROR) << "Failed to read namespace ID";
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return "";
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}
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return ret;
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}
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static bool IsApexUpdatable() {
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static bool updatable = android::sysprop::ApexProperties::updatable().value_or(false);
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return updatable;
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}
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static Result<void> MountDir(const std::string& path, const std::string& mount_path) {
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if (int ret = mkdir(mount_path.c_str(), 0755); ret != 0 && ret != EEXIST) {
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return ErrnoError() << "Could not create mount point " << mount_path;
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}
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if (mount(path.c_str(), mount_path.c_str(), nullptr, MS_BIND, nullptr) != 0) {
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return ErrnoError() << "Could not bind mount " << path << " to " << mount_path;
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}
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return {};
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}
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static Result<void> ActivateFlattenedApexesFrom(const std::string& from_dir,
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const std::string& to_dir) {
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std::unique_ptr<DIR, decltype(&closedir)> dir(opendir(from_dir.c_str()), closedir);
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if (!dir) {
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return {};
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}
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dirent* entry;
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while ((entry = readdir(dir.get())) != nullptr) {
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if (entry->d_name[0] == '.') continue;
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if (entry->d_type == DT_DIR) {
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const std::string apex_path = from_dir + "/" + entry->d_name;
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const std::string mount_path = to_dir + "/" + entry->d_name;
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if (auto result = MountDir(apex_path, mount_path); !result) {
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return result;
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}
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}
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}
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return {};
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}
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static bool ActivateFlattenedApexesIfPossible() {
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if (IsRecoveryMode() || IsApexUpdatable()) {
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return true;
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}
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const std::string kApexTop = "/apex";
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const std::vector<std::string> kBuiltinDirsForApexes = {
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"/system/apex",
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"/system_ext/apex",
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"/product/apex",
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"/vendor/apex",
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};
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for (const auto& dir : kBuiltinDirsForApexes) {
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if (auto result = ActivateFlattenedApexesFrom(dir, kApexTop); !result) {
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LOG(ERROR) << result.error();
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return false;
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}
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}
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// Special casing for the ART APEX
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constexpr const char kArtApexMountPath[] = "/apex/com.android.art";
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static const std::vector<std::string> kArtApexDirNames = {"com.android.art.release",
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"com.android.art.debug"};
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bool success = false;
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for (const auto& name : kArtApexDirNames) {
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std::string path = kApexTop + "/" + name;
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if (access(path.c_str(), F_OK) == 0) {
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if (auto result = MountDir(path, kArtApexMountPath); !result) {
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LOG(ERROR) << result.error();
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return false;
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}
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success = true;
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break;
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}
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}
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if (!success) {
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PLOG(ERROR) << "Failed to bind mount the ART APEX to " << kArtApexMountPath;
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}
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return success;
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}
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static android::base::unique_fd bootstrap_ns_fd;
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static android::base::unique_fd default_ns_fd;
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static std::string bootstrap_ns_id;
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static std::string default_ns_id;
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} // namespace
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bool SetupMountNamespaces() {
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// Set the propagation type of / as shared so that any mounting event (e.g.
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// /data) is by default visible to all processes. When private mounting is
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// needed for /foo/bar, then we will make /foo/bar as a mount point (by
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// bind-mounting by to itself) and set the propagation type of the mount
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// point to private.
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if (!MakeShared("/", true /*recursive*/)) return false;
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// /apex is a private mountpoint to give different sets of APEXes for
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// the bootstrap and default mount namespaces. The processes running with
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// the bootstrap namespace get APEXes from the read-only partition.
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if (!(MakePrivate("/apex"))) return false;
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// /linkerconfig is a private mountpoint to give a different linker configuration
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// based on the mount namespace. Subdirectory will be bind-mounted based on current mount
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// namespace
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if (!(MakePrivate("/linkerconfig"))) return false;
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bootstrap_ns_fd.reset(OpenMountNamespace());
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bootstrap_ns_id = GetMountNamespaceId();
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// When APEXes are updatable (e.g. not-flattened), we create separate mount
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// namespaces for processes that are started before and after the APEX is
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// activated by apexd. In the namespace for pre-apexd processes, small
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// number of essential APEXes (e.g. com.android.runtime) are activated.
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// In the namespace for post-apexd processes, all APEXes are activated.
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bool success = true;
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if (IsApexUpdatable() && !IsRecoveryMode()) {
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// Creating a new namespace by cloning, saving, and switching back to
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// the original namespace.
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if (unshare(CLONE_NEWNS) == -1) {
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PLOG(ERROR) << "Cannot create mount namespace";
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return false;
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}
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default_ns_fd.reset(OpenMountNamespace());
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default_ns_id = GetMountNamespaceId();
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if (setns(bootstrap_ns_fd.get(), CLONE_NEWNS) == -1) {
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PLOG(ERROR) << "Cannot switch back to bootstrap mount namespace";
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return false;
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}
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} else {
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// Otherwise, default == bootstrap
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default_ns_fd.reset(OpenMountNamespace());
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default_ns_id = GetMountNamespaceId();
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}
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success &= ActivateFlattenedApexesIfPossible();
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LOG(INFO) << "SetupMountNamespaces done";
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return success;
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}
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bool SwitchToDefaultMountNamespace() {
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if (IsRecoveryMode()) {
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// we don't have multiple namespaces in recovery mode
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return true;
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}
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if (default_ns_id != GetMountNamespaceId()) {
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if (setns(default_ns_fd.get(), CLONE_NEWNS) == -1) {
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PLOG(ERROR) << "Failed to switch back to the default mount namespace.";
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return false;
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}
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}
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LOG(INFO) << "Switched to default mount namespace";
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return true;
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}
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bool SwitchToBootstrapMountNamespaceIfNeeded() {
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if (IsRecoveryMode()) {
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// we don't have multiple namespaces in recovery mode
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return true;
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}
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if (bootstrap_ns_id != GetMountNamespaceId() && bootstrap_ns_fd.get() != -1 &&
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IsApexUpdatable()) {
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if (setns(bootstrap_ns_fd.get(), CLONE_NEWNS) == -1) {
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PLOG(ERROR) << "Failed to switch to bootstrap mount namespace.";
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return false;
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}
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}
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return true;
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}
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} // namespace init
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} // namespace android
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