init/mount_namespace.cpp - android_system_core - Gitiles

 /*
  * 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 <ApexProperties.sysprop.h>
 #include <android-base/file.h>
 #include <android-base/logging.h>
 #include <android-base/properties.h>
 #include <android-base/result.h>
 #include <android-base/unique_fd.h>

 #include "util.h"

 namespace android {
 namespace init {
 namespace {

 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 IsApexUpdatable() {
     static bool updatable = android::sysprop::ApexProperties::updatable().value_or(false);
     return updatable;
 }

 static Result<void> MountDir(const std::string& path, const std::string& mount_path) {
     if (int ret = mkdir(mount_path.c_str(), 0755); ret != 0 && ret != EEXIST) {
         return ErrnoError() << "Could not create mount point " << mount_path;
     }
     if (mount(path.c_str(), mount_path.c_str(), nullptr, MS_BIND, nullptr) != 0) {
         return ErrnoError() << "Could not bind mount " << path << " to " << mount_path;
     }
     return {};
 }

 static Result<void> ActivateFlattenedApexesFrom(const std::string& from_dir,
                                                 const std::string& to_dir) {
     std::unique_ptr<DIR, decltype(&closedir)> dir(opendir(from_dir.c_str()), closedir);
     if (!dir) {
         return {};
     }
     dirent* entry;
     while ((entry = readdir(dir.get())) != nullptr) {
         if (entry->d_name[0] == '.') continue;
         if (entry->d_type == DT_DIR) {
             const std::string apex_path = from_dir + "/" + entry->d_name;
             const std::string mount_path = to_dir + "/" + entry->d_name;
             if (auto result = MountDir(apex_path, mount_path); !result) {
                 return result;
             }
         }
     }
     return {};
 }

 static bool ActivateFlattenedApexesIfPossible() {
     if (IsRecoveryMode() || IsApexUpdatable()) {
         return true;
     }

     const std::string kApexTop = "/apex";
     const std::vector<std::string> kBuiltinDirsForApexes = {
             "/system/apex",
             "/system_ext/apex",
             "/product/apex",
             "/vendor/apex",
     };

     for (const auto& dir : kBuiltinDirsForApexes) {
         if (auto result = ActivateFlattenedApexesFrom(dir, kApexTop); !result) {
             LOG(ERROR) << result.error();
             return false;
         }
     }
     // Special casing for the ART APEX
     constexpr const char kArtApexMountPath[] = "/apex/com.android.art";
     static const std::vector<std::string> kArtApexDirNames = {"com.android.art.release",
                                                               "com.android.art.debug"};
     bool success = false;
     for (const auto& name : kArtApexDirNames) {
         std::string path = kApexTop + "/" + name;
         if (access(path.c_str(), F_OK) == 0) {
             if (auto result = MountDir(path, kArtApexMountPath); !result) {
                 LOG(ERROR) << result.error();
                 return false;
             }
             success = true;
             break;
         }
     }
     if (!success) {
         PLOG(ERROR) << "Failed to bind mount the ART APEX to " << kArtApexMountPath;
     }
     return success;
 }

 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;

     // /apex is a private mountpoint to give different sets of APEXes for
     // the bootstrap and default mount namespaces. The processes running with
     // the bootstrap namespace get APEXes from the read-only partition.
     if (!(MakePrivate("/apex"))) return false;

     // /linkerconfig is a private mountpoint to give a different linker configuration
     // based on the mount namespace. Subdirectory will be bind-mounted based on current mount
     // namespace
     if (!(MakePrivate("/linkerconfig"))) return false;

     bootstrap_ns_fd.reset(OpenMountNamespace());
     bootstrap_ns_id = GetMountNamespaceId();

     // When APEXes are updatable (e.g. not-flattened), 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, small
     // number of essential APEXes (e.g. com.android.runtime) are activated.
     // In the namespace for post-apexd processes, all APEXes are activated.
     bool success = true;
     if (IsApexUpdatable() && !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();

         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();
     }

     success &= ActivateFlattenedApexesIfPossible();

     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;
         }
     }

     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 &&
         IsApexUpdatable()) {
         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
	/*
	* 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 <ApexProperties.sysprop.h>
	#include <android-base/file.h>
	#include <android-base/logging.h>
	#include <android-base/properties.h>
	#include <android-base/result.h>
	#include <android-base/unique_fd.h>

	#include "util.h"

	namespace android {
	namespace init {
	namespace {

	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 IsApexUpdatable() {
	static bool updatable = android::sysprop::ApexProperties::updatable().value_or(false);
	return updatable;
	}

	static Result<void> MountDir(const std::string& path, const std::string& mount_path) {
	if (int ret = mkdir(mount_path.c_str(), 0755); ret != 0 && ret != EEXIST) {
	return ErrnoError() << "Could not create mount point " << mount_path;
	}
	if (mount(path.c_str(), mount_path.c_str(), nullptr, MS_BIND, nullptr) != 0) {
	return ErrnoError() << "Could not bind mount " << path << " to " << mount_path;
	}
	return {};
	}

	static Result<void> ActivateFlattenedApexesFrom(const std::string& from_dir,
	const std::string& to_dir) {
	std::unique_ptr<DIR, decltype(&closedir)> dir(opendir(from_dir.c_str()), closedir);
	if (!dir) {
	return {};
	}
	dirent* entry;
	while ((entry = readdir(dir.get())) != nullptr) {
	if (entry->d_name[0] == '.') continue;
	if (entry->d_type == DT_DIR) {
	const std::string apex_path = from_dir + "/" + entry->d_name;
	const std::string mount_path = to_dir + "/" + entry->d_name;
	if (auto result = MountDir(apex_path, mount_path); !result) {
	return result;
	}
	}
	}
	return {};
	}

	static bool ActivateFlattenedApexesIfPossible() {
	if (IsRecoveryMode() \|\| IsApexUpdatable()) {
	return true;
	}

	const std::string kApexTop = "/apex";
	const std::vector<std::string> kBuiltinDirsForApexes = {
	"/system/apex",
	"/system_ext/apex",
	"/product/apex",
	"/vendor/apex",
	};

	for (const auto& dir : kBuiltinDirsForApexes) {
	if (auto result = ActivateFlattenedApexesFrom(dir, kApexTop); !result) {
	LOG(ERROR) << result.error();
	return false;
	}
	}
	// Special casing for the ART APEX
	constexpr const char kArtApexMountPath[] = "/apex/com.android.art";
	static const std::vector<std::string> kArtApexDirNames = {"com.android.art.release",
	"com.android.art.debug"};
	bool success = false;
	for (const auto& name : kArtApexDirNames) {
	std::string path = kApexTop + "/" + name;
	if (access(path.c_str(), F_OK) == 0) {
	if (auto result = MountDir(path, kArtApexMountPath); !result) {
	LOG(ERROR) << result.error();
	return false;
	}
	success = true;
	break;
	}
	}
	if (!success) {
	PLOG(ERROR) << "Failed to bind mount the ART APEX to " << kArtApexMountPath;
	}
	return success;
	}

	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;

	// /apex is a private mountpoint to give different sets of APEXes for
	// the bootstrap and default mount namespaces. The processes running with
	// the bootstrap namespace get APEXes from the read-only partition.
	if (!(MakePrivate("/apex"))) return false;

	// /linkerconfig is a private mountpoint to give a different linker configuration
	// based on the mount namespace. Subdirectory will be bind-mounted based on current mount
	// namespace
	if (!(MakePrivate("/linkerconfig"))) return false;

	bootstrap_ns_fd.reset(OpenMountNamespace());
	bootstrap_ns_id = GetMountNamespaceId();

	// When APEXes are updatable (e.g. not-flattened), 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, small
	// number of essential APEXes (e.g. com.android.runtime) are activated.
	// In the namespace for post-apexd processes, all APEXes are activated.
	bool success = true;
	if (IsApexUpdatable() && !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();

	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();
	}

	success &= ActivateFlattenedApexesIfPossible();

	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;
	}
	}

	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 &&
	IsApexUpdatable()) {
	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