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/*
* Copyright (C) 2019 The Android Open Source Project
*
* 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 "mount_namespace.h"
#include <sys/mount.h>
#include <string>
#include <vector>
#include <android-base/file.h>
#include <android-base/logging.h>
#include <android-base/properties.h>
#include <android-base/unique_fd.h>
#include "util.h"
namespace android {
namespace init {
namespace {
static constexpr const char* kLinkerMountPoint = "/bionic/bin/linker";
static constexpr const char* kBootstrapLinkerPath = "/system/bin/bootstrap/linker";
static constexpr const char* kRuntimeLinkerPath = "/apex/com.android.runtime/bin/linker";
static constexpr const char* kBionicLibsMountPointDir = "/bionic/lib/";
static constexpr const char* kBootstrapBionicLibsDir = "/system/lib/bootstrap/";
static constexpr const char* kRuntimeBionicLibsDir = "/apex/com.android.runtime/lib/bionic/";
static constexpr const char* kLinkerMountPoint64 = "/bionic/bin/linker64";
static constexpr const char* kBootstrapLinkerPath64 = "/system/bin/bootstrap/linker64";
static constexpr const char* kRuntimeLinkerPath64 = "/apex/com.android.runtime/bin/linker64";
static constexpr const char* kBionicLibsMountPointDir64 = "/bionic/lib64/";
static constexpr const char* kBootstrapBionicLibsDir64 = "/system/lib64/bootstrap/";
static constexpr const char* kRuntimeBionicLibsDir64 = "/apex/com.android.runtime/lib64/bionic/";
static const std::vector<std::string> kBionicLibFileNames = {"libc.so", "libm.so", "libdl.so"};
static bool BindMount(const std::string& source, const std::string& mount_point,
bool recursive = false) {
unsigned long mountflags = MS_BIND;
if (recursive) {
mountflags |= MS_REC;
}
if (mount(source.c_str(), mount_point.c_str(), nullptr, mountflags, nullptr) == -1) {
PLOG(ERROR) << "Could not bind-mount " << source << " to " << mount_point;
return false;
}
return true;
}
static bool MakeShared(const std::string& mount_point, bool recursive = false) {
unsigned long mountflags = MS_SHARED;
if (recursive) {
mountflags |= MS_REC;
}
if (mount(nullptr, mount_point.c_str(), nullptr, mountflags, nullptr) == -1) {
PLOG(ERROR) << "Failed to change propagation type to shared";
return false;
}
return true;
}
static bool MakePrivate(const std::string& mount_point, bool recursive = false) {
unsigned long mountflags = MS_PRIVATE;
if (recursive) {
mountflags |= MS_REC;
}
if (mount(nullptr, mount_point.c_str(), nullptr, mountflags, nullptr) == -1) {
PLOG(ERROR) << "Failed to change propagation type to private";
return false;
}
return true;
}
static int OpenMountNamespace() {
int fd = open("/proc/self/ns/mnt", O_RDONLY | O_CLOEXEC);
if (fd < 0) {
PLOG(ERROR) << "Cannot open fd for current mount namespace";
}
return fd;
}
static std::string GetMountNamespaceId() {
std::string ret;
if (!android::base::Readlink("/proc/self/ns/mnt", &ret)) {
PLOG(ERROR) << "Failed to read namespace ID";
return "";
}
return ret;
}
static bool BindMountBionic(const std::string& linker_source, const std::string& lib_dir_source,
const std::string& linker_mount_point,
const std::string& lib_mount_dir) {
if (access(linker_source.c_str(), F_OK) != 0) {
PLOG(INFO) << linker_source << " does not exist. skipping mounting bionic there.";
// This can happen for 64-bit bionic in 32-bit only device.
// It is okay to skip mounting the 64-bit bionic.
return true;
}
if (!BindMount(linker_source, linker_mount_point)) {
return false;
}
if (!MakePrivate(linker_mount_point)) {
return false;
}
for (const auto& libname : kBionicLibFileNames) {
std::string mount_point = lib_mount_dir + libname;
std::string source = lib_dir_source + libname;
if (!BindMount(source, mount_point)) {
return false;
}
if (!MakePrivate(mount_point)) {
return false;
}
}
return true;
}
static bool IsBionicUpdatable() {
static bool result = android::base::GetBoolProperty("ro.apex.IsBionicUpdatable", false);
return result;
}
static android::base::unique_fd bootstrap_ns_fd;
static android::base::unique_fd default_ns_fd;
static std::string bootstrap_ns_id;
static std::string default_ns_id;
} // namespace
bool SetupMountNamespaces() {
// Set the propagation type of / as shared so that any mounting event (e.g.
// /data) is by default visible to all processes. When private mounting is
// needed for /foo/bar, then we will make /foo/bar as a mount point (by
// bind-mounting by to itself) and set the propagation type of the mount
// point to private.
if (!MakeShared("/", true /*recursive*/)) return false;
// Since different files (bootstrap or runtime APEX) should be mounted to
// the same mount point paths (e.g. /bionic/bin/linker, /bionic/lib/libc.so,
// etc.) across the two mount namespaces, we create a private mount point at
// /bionic so that a mount event for the bootstrap bionic in the mount
// namespace for pre-apexd processes is not propagated to the other mount
// namespace for post-apexd process, and vice versa.
//
// Other mount points other than /bionic, however, are all still shared.
if (!BindMount("/bionic", "/bionic", true /*recursive*/)) return false;
if (!MakePrivate("/bionic")) return false;
// Bind-mount bootstrap bionic.
if (!BindMountBionic(kBootstrapLinkerPath, kBootstrapBionicLibsDir, kLinkerMountPoint,
kBionicLibsMountPointDir))
return false;
if (!BindMountBionic(kBootstrapLinkerPath64, kBootstrapBionicLibsDir64, kLinkerMountPoint64,
kBionicLibsMountPointDir64))
return false;
bootstrap_ns_fd.reset(OpenMountNamespace());
bootstrap_ns_id = GetMountNamespaceId();
// When bionic is updatable via the runtime APEX, we create separate mount
// namespaces for processes that are started before and after the APEX is
// activated by apexd. In the namespace for pre-apexd processes, the bionic
// from the /system partition (that we call bootstrap bionic) is
// bind-mounted. In the namespace for post-apexd processes, the bionic from
// the runtime APEX is bind-mounted.
bool success = true;
if (IsBionicUpdatable() && !IsRecoveryMode()) {
// Creating a new namespace by cloning, saving, and switching back to
// the original namespace.
if (unshare(CLONE_NEWNS) == -1) {
PLOG(ERROR) << "Cannot create mount namespace";
return false;
}
default_ns_fd.reset(OpenMountNamespace());
default_ns_id = GetMountNamespaceId();
// By this unmount, the bootstrap bionic are not mounted in the default
// mount namespace.
if (umount2("/bionic", MNT_DETACH) == -1) {
PLOG(ERROR) << "Cannot unmount /bionic";
// Don't return here. We have to switch back to the bootstrap
// namespace.
success = false;
}
if (setns(bootstrap_ns_fd.get(), CLONE_NEWNS) == -1) {
PLOG(ERROR) << "Cannot switch back to bootstrap mount namespace";
return false;
}
} else {
// Otherwise, default == bootstrap
default_ns_fd.reset(OpenMountNamespace());
default_ns_id = GetMountNamespaceId();
}
LOG(INFO) << "SetupMountNamespaces done";
return success;
}
bool SwitchToDefaultMountNamespace() {
if (IsRecoveryMode()) {
// we don't have multiple namespaces in recovery mode
return true;
}
if (default_ns_id != GetMountNamespaceId()) {
if (setns(default_ns_fd.get(), CLONE_NEWNS) == -1) {
PLOG(ERROR) << "Failed to switch back to the default mount namespace.";
return false;
}
}
// Bind-mount bionic from the runtime APEX since it is now available. Note
// that in case of IsBionicUpdatable() == false, these mounts are over the
// existing existing bind mounts for the bootstrap bionic, which effectively
// becomes hidden.
if (!BindMountBionic(kRuntimeLinkerPath, kRuntimeBionicLibsDir, kLinkerMountPoint,
kBionicLibsMountPointDir))
return false;
if (!BindMountBionic(kRuntimeLinkerPath64, kRuntimeBionicLibsDir64, kLinkerMountPoint64,
kBionicLibsMountPointDir64))
return false;
LOG(INFO) << "Switched to default mount namespace";
return true;
}
bool SwitchToBootstrapMountNamespaceIfNeeded() {
if (IsRecoveryMode()) {
// we don't have multiple namespaces in recovery mode
return true;
}
if (bootstrap_ns_id != GetMountNamespaceId() && bootstrap_ns_fd.get() != -1 &&
IsBionicUpdatable()) {
if (setns(bootstrap_ns_fd.get(), CLONE_NEWNS) == -1) {
PLOG(ERROR) << "Failed to switch to bootstrap mount namespace.";
return false;
}
}
return true;
}
} // namespace init
} // namespace android