CommandListener.cpp

/*
 * Copyright (C) 2008 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 <stdlib.h>
#include <sys/mount.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <fs_mgr.h>
#include <stdio.h>
#include <string.h>
#include <stdint.h>
#include <inttypes.h>
#include <ctype.h>

#define LOG_TAG "VoldCmdListener"

#include <android-base/logging.h>
#include <android-base/stringprintf.h>
#include <android-base/unique_fd.h>
#include <cutils/fs.h>

#include <sysutils/SocketClient.h>
#include <private/android_filesystem_config.h>

#include "CommandListener.h"
#include "VolumeManager.h"
#include "VolumeBase.h"
#include "ResponseCode.h"
#include "Process.h"
#include "Loop.h"
#include "Devmapper.h"
#include "MoveTask.h"
#include "TrimTask.h"

#define DUMP_ARGS 0
#define DEBUG_APPFUSE 0

using android::base::unique_fd;

CommandListener::CommandListener() :
                 FrameworkListener("vold", true) {
    registerCmd(new DumpCmd());
    registerCmd(new VolumeCmd());
    registerCmd(new AsecCmd());
    registerCmd(new ObbCmd());
    registerCmd(new StorageCmd());
    registerCmd(new FstrimCmd());
    registerCmd(new AppFuseCmd());
}

#if DUMP_ARGS
void CommandListener::dumpArgs(int argc, char **argv, int argObscure) {
    char buffer[4096];
    char *p = buffer;

    memset(buffer, 0, sizeof(buffer));
    int i;
    for (i = 0; i < argc; i++) {
        unsigned int len = strlen(argv[i]) + 1; // Account for space
        if (i == argObscure) {
            len += 2; // Account for {}
        }
        if (((p - buffer) + len) < (sizeof(buffer)-1)) {
            if (i == argObscure) {
                *p++ = '{';
                *p++ = '}';
                *p++ = ' ';
                continue;
            }
            strcpy(p, argv[i]);
            p+= strlen(argv[i]);
            if (i != (argc -1)) {
                *p++ = ' ';
            }
        }
    }
    SLOGD("%s", buffer);
}
#else
void CommandListener::dumpArgs(int /*argc*/, char ** /*argv*/, int /*argObscure*/) { }
#endif

int CommandListener::sendGenericOkFail(SocketClient *cli, int cond) {
    if (!cond) {
        return cli->sendMsg(ResponseCode::CommandOkay, "Command succeeded", false);
    } else {
        return cli->sendMsg(ResponseCode::OperationFailed, "Command failed", false);
    }
}

CommandListener::DumpCmd::DumpCmd() :
                 VoldCommand("dump") {
}

int CommandListener::DumpCmd::runCommand(SocketClient *cli,
                                         int /*argc*/, char ** /*argv*/) {
    cli->sendMsg(0, "Dumping loop status", false);
    if (Loop::dumpState(cli)) {
        cli->sendMsg(ResponseCode::CommandOkay, "Loop dump failed", true);
    }
    cli->sendMsg(0, "Dumping DM status", false);
    if (Devmapper::dumpState(cli)) {
        cli->sendMsg(ResponseCode::CommandOkay, "Devmapper dump failed", true);
    }
    cli->sendMsg(0, "Dumping mounted filesystems", false);
    FILE *fp = fopen("/proc/mounts", "re");
    if (fp) {
        char line[1024];
        while (fgets(line, sizeof(line), fp)) {
            line[strlen(line)-1] = '\0';
            cli->sendMsg(0, line, false);;
        }
        fclose(fp);
    }

    cli->sendMsg(ResponseCode::CommandOkay, "dump complete", false);
    return 0;
}

CommandListener::VolumeCmd::VolumeCmd() :
                 VoldCommand("volume") {
}

int CommandListener::VolumeCmd::runCommand(SocketClient *cli,
                                           int argc, char **argv) {
    dumpArgs(argc, argv, -1);

    if (argc < 2) {
        cli->sendMsg(ResponseCode::CommandSyntaxError, "Missing Argument", false);
        return 0;
    }

    VolumeManager *vm = VolumeManager::Instance();
    std::lock_guard<std::mutex> lock(vm->getLock());

    // TODO: tease out methods not directly related to volumes

    std::string cmd(argv[1]);
    if (cmd == "reset") {
        return sendGenericOkFail(cli, vm->reset());

    } else if (cmd == "shutdown") {
        return sendGenericOkFail(cli, vm->shutdown());

    } else if (cmd == "debug") {
        return sendGenericOkFail(cli, vm->setDebug(true));

    } else if (cmd == "partition" && argc > 3) {
        // partition [diskId] [public|private|mixed] [ratio]
        std::string id(argv[2]);
        auto disk = vm->findDisk(id);
        if (disk == nullptr) {
            return cli->sendMsg(ResponseCode::CommandSyntaxError, "Unknown disk", false);
        }

        std::string type(argv[3]);
        if (type == "public") {
            return sendGenericOkFail(cli, disk->partitionPublic());
        } else if (type == "private") {
            return sendGenericOkFail(cli, disk->partitionPrivate());
        } else if (type == "mixed") {
            if (argc < 4) {
                return cli->sendMsg(ResponseCode::CommandSyntaxError, nullptr, false);
            }
            int frac = atoi(argv[4]);
            return sendGenericOkFail(cli, disk->partitionMixed(frac));
        } else {
            return cli->sendMsg(ResponseCode::CommandSyntaxError, nullptr, false);
        }

    } else if (cmd == "mkdirs" && argc > 2) {
        // mkdirs [path]
        return sendGenericOkFail(cli, vm->mkdirs(argv[2]));

    } else if (cmd == "user_added" && argc > 3) {
        // user_added [user] [serial]
        return sendGenericOkFail(cli, vm->onUserAdded(atoi(argv[2]), atoi(argv[3])));

    } else if (cmd == "user_removed" && argc > 2) {
        // user_removed [user]
        return sendGenericOkFail(cli, vm->onUserRemoved(atoi(argv[2])));

    } else if (cmd == "user_started" && argc > 2) {
        // user_started [user]
        return sendGenericOkFail(cli, vm->onUserStarted(atoi(argv[2])));

    } else if (cmd == "user_stopped" && argc > 2) {
        // user_stopped [user]
        return sendGenericOkFail(cli, vm->onUserStopped(atoi(argv[2])));

    } else if (cmd == "mount" && argc > 2) {
        // mount [volId] [flags] [user]
        std::string id(argv[2]);
        auto vol = vm->findVolume(id);
        if (vol == nullptr) {
            return cli->sendMsg(ResponseCode::CommandSyntaxError, "Unknown volume", false);
        }

        int mountFlags = (argc > 3) ? atoi(argv[3]) : 0;
        userid_t mountUserId = (argc > 4) ? atoi(argv[4]) : -1;

        vol->setMountFlags(mountFlags);
        vol->setMountUserId(mountUserId);

        int res = vol->mount();
        if (mountFlags & android::vold::VolumeBase::MountFlags::kPrimary) {
            vm->setPrimary(vol);
        }
        return sendGenericOkFail(cli, res);

    } else if (cmd == "unmount" && argc > 2) {
        // unmount [volId] [detach]
        std::string id(argv[2]);
        auto vol = vm->findVolume(id);
        if (vol == nullptr) {
            return cli->sendMsg(ResponseCode::CommandSyntaxError, "Unknown volume", false);
        }
        bool detach = (argc > 3 && !strcmp(argv[3], "detach"));

        return sendGenericOkFail(cli, vol->unmount(detach));

    } else if (cmd == "format" && argc > 3) {
        // format [volId] [fsType|auto]
        std::string id(argv[2]);
        std::string fsType(argv[3]);
        auto vol = vm->findVolume(id);
        if (vol == nullptr) {
            return cli->sendMsg(ResponseCode::CommandSyntaxError, "Unknown volume", false);
        }

        return sendGenericOkFail(cli, vol->format(fsType));

    } else if (cmd == "move_storage" && argc > 3) {
        // move_storage [fromVolId] [toVolId]
        auto fromVol = vm->findVolume(std::string(argv[2]));
        auto toVol = vm->findVolume(std::string(argv[3]));
        if (fromVol == nullptr || toVol == nullptr) {
            return cli->sendMsg(ResponseCode::CommandSyntaxError, "Unknown volume", false);
        }

        (new android::vold::MoveTask(fromVol, toVol))->start();
        return sendGenericOkFail(cli, 0);

    } else if (cmd == "benchmark" && argc > 2) {
        // benchmark [volId]
        std::string id(argv[2]);
        nsecs_t res = vm->benchmarkPrivate(id);
        return cli->sendMsg(ResponseCode::CommandOkay,
                android::base::StringPrintf("%" PRId64, res).c_str(), false);

    } else if (cmd == "forget_partition" && argc > 2) {
        // forget_partition [partGuid]
        std::string partGuid(argv[2]);
        return sendGenericOkFail(cli, vm->forgetPartition(partGuid));

    } else if (cmd == "remount_uid" && argc > 3) {
        // remount_uid [uid] [none|default|read|write]
        uid_t uid = atoi(argv[2]);
        std::string mode(argv[3]);
        return sendGenericOkFail(cli, vm->remountUid(uid, mode));
    }

    return cli->sendMsg(ResponseCode::CommandSyntaxError, nullptr, false);
}

CommandListener::StorageCmd::StorageCmd() :
                 VoldCommand("storage") {
}

int CommandListener::StorageCmd::runCommand(SocketClient *cli,
                                                      int argc, char **argv) {
    /* Guarantied to be initialized by vold's main() before the CommandListener is active */
    extern struct fstab *fstab;

    dumpArgs(argc, argv, -1);

    if (argc < 2) {
        cli->sendMsg(ResponseCode::CommandSyntaxError, "Missing Argument", false);
        return 0;
    }

    if (!strcmp(argv[1], "mountall")) {
        if (argc != 2) {
            cli->sendMsg(ResponseCode::CommandSyntaxError, "Usage: mountall", false);
            return 0;
        }
        fs_mgr_mount_all(fstab, MOUNT_MODE_DEFAULT);
        cli->sendMsg(ResponseCode::CommandOkay, "Mountall ran successfully", false);
        return 0;
    }
    if (!strcmp(argv[1], "users")) {
        DIR *dir;
        struct dirent *de;

        if (argc < 3) {
            cli->sendMsg(ResponseCode::CommandSyntaxError, "Missing Argument: user <mountpoint>", false);
            return 0;
        }
        if (!(dir = opendir("/proc"))) {
            cli->sendMsg(ResponseCode::OperationFailed, "Failed to open /proc", true);
            return 0;
        }

        while ((de = readdir(dir))) {
            int pid = Process::getPid(de->d_name);

            if (pid < 0) {
                continue;
            }

            char processName[255];
            Process::getProcessName(pid, processName, sizeof(processName));

            if (Process::checkFileDescriptorSymLinks(pid, argv[2]) ||
                Process::checkFileMaps(pid, argv[2]) ||
                Process::checkSymLink(pid, argv[2], "cwd") ||
                Process::checkSymLink(pid, argv[2], "root") ||
                Process::checkSymLink(pid, argv[2], "exe")) {

                char msg[1024];
                snprintf(msg, sizeof(msg), "%d %s", pid, processName);
                cli->sendMsg(ResponseCode::StorageUsersListResult, msg, false);
            }
        }
        closedir(dir);
        cli->sendMsg(ResponseCode::CommandOkay, "Storage user list complete", false);
    } else {
        cli->sendMsg(ResponseCode::CommandSyntaxError, "Unknown storage cmd", false);
    }
    return 0;
}

CommandListener::AsecCmd::AsecCmd() :
                 VoldCommand("asec") {
}

void CommandListener::AsecCmd::listAsecsInDirectory(SocketClient *cli, const char *directory) {
    DIR *d = opendir(directory);

    if (!d) {
        cli->sendMsg(ResponseCode::OperationFailed, "Failed to open asec dir", true);
        return;
    }

    size_t dirent_len = offsetof(struct dirent, d_name) +
            fpathconf(dirfd(d), _PC_NAME_MAX) + 1;

    struct dirent *dent = (struct dirent *) malloc(dirent_len);
    if (dent == NULL) {
        cli->sendMsg(ResponseCode::OperationFailed, "Failed to allocate memory", true);
        return;
    }

    struct dirent *result;

    while (!readdir_r(d, dent, &result) && result != NULL) {
        if (dent->d_name[0] == '.')
            continue;
        if (dent->d_type != DT_REG)
            continue;
        size_t name_len = strlen(dent->d_name);
        if (name_len > 5 && name_len < 260 &&
                !strcmp(&dent->d_name[name_len - 5], ".asec")) {
            char id[255];
            memset(id, 0, sizeof(id));
            strlcpy(id, dent->d_name, name_len - 4);
            cli->sendMsg(ResponseCode::AsecListResult, id, false);
        }
    }
    closedir(d);

    free(dent);
}

int CommandListener::AsecCmd::runCommand(SocketClient *cli,
                                                      int argc, char **argv) {
    if (argc < 2) {
        cli->sendMsg(ResponseCode::CommandSyntaxError, "Missing Argument", false);
        return 0;
    }

    VolumeManager *vm = VolumeManager::Instance();
    int rc = 0;

    if (!strcmp(argv[1], "list")) {
        dumpArgs(argc, argv, -1);

        listAsecsInDirectory(cli, VolumeManager::SEC_ASECDIR_EXT);
        listAsecsInDirectory(cli, VolumeManager::SEC_ASECDIR_INT);
    } else if (!strcmp(argv[1], "create")) {
        dumpArgs(argc, argv, 5);
        if (argc != 8) {
            cli->sendMsg(ResponseCode::CommandSyntaxError,
                    "Usage: asec create <container-id> <size_mb> <fstype> <key> <ownerUid> "
                    "<isExternal>", false);
            return 0;
        }

        unsigned long numSectors = (atoi(argv[3]) * (1024 * 1024)) / 512;
        const bool isExternal = (atoi(argv[7]) == 1);
        rc = vm->createAsec(argv[2], numSectors, argv[4], argv[5], atoi(argv[6]), isExternal);
    } else if (!strcmp(argv[1], "resize")) {
        dumpArgs(argc, argv, -1);
        if (argc != 5) {
            cli->sendMsg(ResponseCode::CommandSyntaxError, "Usage: asec resize <container-id> <size_mb> <key>", false);
            return 0;
        }
        unsigned long numSectors = (atoi(argv[3]) * (1024 * 1024)) / 512;
        rc = vm->resizeAsec(argv[2], numSectors, argv[4]);
    } else if (!strcmp(argv[1], "finalize")) {
        dumpArgs(argc, argv, -1);
        if (argc != 3) {
            cli->sendMsg(ResponseCode::CommandSyntaxError, "Usage: asec finalize <container-id>", false);
            return 0;
        }
        rc = vm->finalizeAsec(argv[2]);
    } else if (!strcmp(argv[1], "fixperms")) {
        dumpArgs(argc, argv, -1);
        if  (argc != 5) {
            cli->sendMsg(ResponseCode::CommandSyntaxError, "Usage: asec fixperms <container-id> <gid> <filename>", false);
            return 0;
        }

        char *endptr;
        gid_t gid = (gid_t) strtoul(argv[3], &endptr, 10);
        if (*endptr != '\0') {
            cli->sendMsg(ResponseCode::CommandSyntaxError, "Usage: asec fixperms <container-id> <gid> <filename>", false);
            return 0;
        }

        rc = vm->fixupAsecPermissions(argv[2], gid, argv[4]);
    } else if (!strcmp(argv[1], "destroy")) {
        dumpArgs(argc, argv, -1);
        if (argc < 3) {
            cli->sendMsg(ResponseCode::CommandSyntaxError, "Usage: asec destroy <container-id> [force]", false);
            return 0;
        }
        bool force = false;
        if (argc > 3 && !strcmp(argv[3], "force")) {
            force = true;
        }
        rc = vm->destroyAsec(argv[2], force);
    } else if (!strcmp(argv[1], "mount")) {
        dumpArgs(argc, argv, 3);
        if (argc != 6) {
            cli->sendMsg(ResponseCode::CommandSyntaxError,
                    "Usage: asec mount <namespace-id> <key> <ownerUid> <ro|rw>", false);
            return 0;
        }
        bool readOnly = true;
        if (!strcmp(argv[5], "rw")) {
            readOnly = false;
        }
        rc = vm->mountAsec(argv[2], argv[3], atoi(argv[4]), readOnly);
    } else if (!strcmp(argv[1], "unmount")) {
        dumpArgs(argc, argv, -1);
        if (argc < 3) {
            cli->sendMsg(ResponseCode::CommandSyntaxError, "Usage: asec unmount <container-id> [force]", false);
            return 0;
        }
        bool force = false;
        if (argc > 3 && !strcmp(argv[3], "force")) {
            force = true;
        }
        rc = vm->unmountAsec(argv[2], force);
    } else if (!strcmp(argv[1], "rename")) {
        dumpArgs(argc, argv, -1);
        if (argc != 4) {
            cli->sendMsg(ResponseCode::CommandSyntaxError,
                    "Usage: asec rename <old_id> <new_id>", false);
            return 0;
        }
        rc = vm->renameAsec(argv[2], argv[3]);
    } else if (!strcmp(argv[1], "path")) {
        dumpArgs(argc, argv, -1);
        if (argc != 3) {
            cli->sendMsg(ResponseCode::CommandSyntaxError, "Usage: asec path <container-id>", false);
            return 0;
        }
        char path[255];

        if (!(rc = vm->getAsecMountPath(argv[2], path, sizeof(path)))) {
            cli->sendMsg(ResponseCode::AsecPathResult, path, false);
            return 0;
        }
    } else if (!strcmp(argv[1], "fspath")) {
        dumpArgs(argc, argv, -1);
        if (argc != 3) {
            cli->sendMsg(ResponseCode::CommandSyntaxError, "Usage: asec fspath <container-id>", false);
            return 0;
        }
        char path[255];

        if (!(rc = vm->getAsecFilesystemPath(argv[2], path, sizeof(path)))) {
            cli->sendMsg(ResponseCode::AsecPathResult, path, false);
            return 0;
        }
    } else {
        dumpArgs(argc, argv, -1);
        cli->sendMsg(ResponseCode::CommandSyntaxError, "Unknown asec cmd", false);
    }

    if (!rc) {
        cli->sendMsg(ResponseCode::CommandOkay, "asec operation succeeded", false);
    } else {
        rc = ResponseCode::convertFromErrno();
        cli->sendMsg(rc, "asec operation failed", true);
    }

    return 0;
}

CommandListener::ObbCmd::ObbCmd() :
                 VoldCommand("obb") {
}

int CommandListener::ObbCmd::runCommand(SocketClient *cli,
                                                      int argc, char **argv) {
    if (argc < 2) {
        cli->sendMsg(ResponseCode::CommandSyntaxError, "Missing Argument", false);
        return 0;
    }

    VolumeManager *vm = VolumeManager::Instance();
    int rc = 0;

    if (!strcmp(argv[1], "list")) {
        dumpArgs(argc, argv, -1);

        rc = vm->listMountedObbs(cli);
    } else if (!strcmp(argv[1], "mount")) {
            dumpArgs(argc, argv, 3);
            if (argc != 5) {
                cli->sendMsg(ResponseCode::CommandSyntaxError,
                        "Usage: obb mount <filename> <key> <ownerGid>", false);
                return 0;
            }
            rc = vm->mountObb(argv[2], argv[3], atoi(argv[4]));
    } else if (!strcmp(argv[1], "unmount")) {
        dumpArgs(argc, argv, -1);
        if (argc < 3) {
            cli->sendMsg(ResponseCode::CommandSyntaxError, "Usage: obb unmount <source file> [force]", false);
            return 0;
        }
        bool force = false;
        if (argc > 3 && !strcmp(argv[3], "force")) {
            force = true;
        }
        rc = vm->unmountObb(argv[2], force);
    } else if (!strcmp(argv[1], "path")) {
        dumpArgs(argc, argv, -1);
        if (argc != 3) {
            cli->sendMsg(ResponseCode::CommandSyntaxError, "Usage: obb path <source file>", false);
            return 0;
        }
        char path[255];

        if (!(rc = vm->getObbMountPath(argv[2], path, sizeof(path)))) {
            cli->sendMsg(ResponseCode::AsecPathResult, path, false);
            return 0;
        }
    } else {
        dumpArgs(argc, argv, -1);
        cli->sendMsg(ResponseCode::CommandSyntaxError, "Unknown obb cmd", false);
    }

    if (!rc) {
        cli->sendMsg(ResponseCode::CommandOkay, "obb operation succeeded", false);
    } else {
        rc = ResponseCode::convertFromErrno();
        cli->sendMsg(rc, "obb operation failed", true);
    }

    return 0;
}

CommandListener::FstrimCmd::FstrimCmd() :
                 VoldCommand("fstrim") {
}
int CommandListener::FstrimCmd::runCommand(SocketClient *cli,
                                                      int argc, char **argv) {
    if ((cli->getUid() != 0) && (cli->getUid() != AID_SYSTEM)) {
        cli->sendMsg(ResponseCode::CommandNoPermission, "No permission to run fstrim commands", false);
        return 0;
    }

    if (argc < 2) {
        cli->sendMsg(ResponseCode::CommandSyntaxError, "Missing Argument", false);
        return 0;
    }

    VolumeManager *vm = VolumeManager::Instance();
    std::lock_guard<std::mutex> lock(vm->getLock());

    int flags = 0;

    std::string cmd(argv[1]);
    if (cmd == "dotrim") {
        flags = 0;
    } else if (cmd == "dotrimbench") {
        flags = android::vold::TrimTask::Flags::kBenchmarkAfter;
    } else if (cmd == "dodtrim") {
        flags = android::vold::TrimTask::Flags::kDeepTrim;
    } else if (cmd == "dodtrimbench") {
        flags = android::vold::TrimTask::Flags::kDeepTrim
                | android::vold::TrimTask::Flags::kBenchmarkAfter;
    }

    (new android::vold::TrimTask(flags))->start();
    return sendGenericOkFail(cli, 0);
}

static size_t kAppFuseMaxMountPointName = 32;

static android::status_t getMountPath(uid_t uid, const std::string& name, std::string* path) {
    if (name.size() > kAppFuseMaxMountPointName) {
        LOG(ERROR) << "AppFuse mount name is too long.";
        return -EINVAL;
    }
    for (size_t i = 0; i < name.size(); i++) {
        if (!isalnum(name[i])) {
            LOG(ERROR) << "AppFuse mount name contains invalid character.";
            return -EINVAL;
        }
    }
    *path = android::base::StringPrintf("/mnt/appfuse/%d_%s", uid, name.c_str());
    return android::OK;
}

static android::status_t mountInNamespace(uid_t uid, int device_fd, const std::string& path) {
    // Remove existing mount.
    android::vold::ForceUnmount(path);

    const auto opts = android::base::StringPrintf(
            "fd=%i,"
            "rootmode=40000,"
            "default_permissions,"
            "allow_other,"
            "user_id=%d,group_id=%d,"
            "context=\"u:object_r:app_fuse_file:s0\","
            "fscontext=u:object_r:app_fusefs:s0",
            device_fd,
            uid,
            uid);

    const int result = TEMP_FAILURE_RETRY(mount(
            "/dev/fuse", path.c_str(), "fuse",
            MS_NOSUID | MS_NODEV | MS_NOEXEC | MS_NOATIME, opts.c_str()));
    if (result != 0) {
        PLOG(ERROR) << "Failed to mount " << path;
        return -errno;
    }

    return android::OK;
}

static android::status_t runCommandInNamespace(const std::string& command,
                                               uid_t uid,
                                               pid_t pid,
                                               const std::string& path,
                                               int device_fd) {
    if (DEBUG_APPFUSE) {
        LOG(DEBUG) << "Run app fuse command " << command << " for the path " << path
                   << " in namespace " << uid;
    }

    unique_fd dir(open("/proc", O_RDONLY | O_DIRECTORY | O_CLOEXEC));
    if (dir.get() == -1) {
        PLOG(ERROR) << "Failed to open /proc";
        return -errno;
    }

    // Obtains process file descriptor.
    const std::string pid_str = android::base::StringPrintf("%d", pid);
    const unique_fd pid_fd(
            openat(dir.get(), pid_str.c_str(), O_RDONLY | O_DIRECTORY | O_CLOEXEC));
    if (pid_fd.get() == -1) {
        PLOG(ERROR) << "Failed to open /proc/" << pid;
        return -errno;
    }

    // Check UID of process.
    {
        struct stat sb;
        const int result = fstat(pid_fd.get(), &sb);
        if (result == -1) {
            PLOG(ERROR) << "Failed to stat /proc/" << pid;
            return -errno;
        }
        if (sb.st_uid != AID_SYSTEM) {
            LOG(ERROR) << "Only system can mount appfuse. UID expected=" << AID_SYSTEM
                    << ", actual=" << sb.st_uid;
            return -EPERM;
        }
    }

    // Matches so far, but refuse to touch if in root namespace
    {
        char rootName[PATH_MAX];
        char pidName[PATH_MAX];
        const int root_result =
                android::vold::SaneReadLinkAt(dir.get(), "1/ns/mnt", rootName, PATH_MAX);
        const int pid_result =
                android::vold::SaneReadLinkAt(pid_fd.get(), "ns/mnt", pidName, PATH_MAX);
        if (root_result == -1) {
            LOG(ERROR) << "Failed to readlink for /proc/1/ns/mnt";
            return -EPERM;
        }
        if (pid_result == -1) {
            LOG(ERROR) << "Failed to readlink for /proc/" << pid << "/ns/mnt";
            return -EPERM;
        }
        if (!strcmp(rootName, pidName)) {
            LOG(ERROR) << "Don't mount appfuse in root namespace";
            return -EPERM;
        }
    }

    // We purposefully leave the namespace open across the fork
    unique_fd ns_fd(openat(pid_fd.get(), "ns/mnt", O_RDONLY)); // not O_CLOEXEC
    if (ns_fd.get() < 0) {
        PLOG(ERROR) << "Failed to open namespace for /proc/" << pid << "/ns/mnt";
        return -errno;
    }

    int child = fork();
    if (child == 0) {
        if (setns(ns_fd.get(), CLONE_NEWNS) != 0) {
            PLOG(ERROR) << "Failed to setns";
            _exit(-errno);
        }

        if (command == "mount") {
            _exit(mountInNamespace(uid, device_fd, path));
        } else if (command == "unmount") {
            // If it's just after all FD opened on mount point are closed, umount2 can fail with
            // EBUSY. To avoid the case, specify MNT_DETACH.
            if (umount2(path.c_str(), UMOUNT_NOFOLLOW | MNT_DETACH) != 0 &&
                    errno != EINVAL && errno != ENOENT) {
                PLOG(ERROR) << "Failed to unmount directory.";
                _exit(-errno);
            }
            if (rmdir(path.c_str()) != 0) {
                PLOG(ERROR) << "Failed to remove the mount directory.";
                _exit(-errno);
            }
            _exit(android::OK);
        } else {
            LOG(ERROR) << "Unknown appfuse command " << command;
            _exit(-EPERM);
        }
    }

    if (child == -1) {
        PLOG(ERROR) << "Failed to folk child process";
        return -errno;
    }

    android::status_t status;
    TEMP_FAILURE_RETRY(waitpid(child, &status, 0));

    return status;
}

CommandListener::AppFuseCmd::AppFuseCmd() : VoldCommand("appfuse") {}

int CommandListener::AppFuseCmd::runCommand(SocketClient *cli, int argc, char **argv) {
    if (argc < 2) {
        cli->sendMsg(ResponseCode::CommandSyntaxError, "Missing argument", false);
        return 0;
    }

    const std::string command(argv[1]);

    if (command == "mount" && argc == 5) {
        const uid_t uid = atoi(argv[2]);
        const pid_t pid = atoi(argv[3]);
        const std::string name(argv[4]);

        // Check mount point name.
        std::string path;
        if (getMountPath(uid, name, &path) != android::OK) {
            return cli->sendMsg(ResponseCode::CommandParameterError,
                                "Invalid mount point name.",
                                false);
        }

        // Create directories.
        {
            const android::status_t result = android::vold::PrepareDir(path, 0700, 0, 0);
            if (result != android::OK) {
                PLOG(ERROR) << "Failed to prepare directory " << path;
                return sendGenericOkFail(cli, result);
            }
        }

        // Open device FD.
        unique_fd device_fd(open("/dev/fuse", O_RDWR)); // not O_CLOEXEC
        if (device_fd.get() == -1) {
            PLOG(ERROR) << "Failed to open /dev/fuse";
            return sendGenericOkFail(cli, -errno);
        }

        // Mount.
        {
            const android::status_t result =
                    runCommandInNamespace(command, uid, pid, path, device_fd.get());
            if (result != android::OK) {
                return sendGenericOkFail(cli, result);
            }
        }

        return sendFd(cli, device_fd.get());
    } else if (command == "unmount" && argc == 5) {
        const uid_t uid = atoi(argv[2]);
        const uid_t pid = atoi(argv[3]);
        const std::string name(argv[4]);

        // Check mount point name.
        std::string path;
        if (getMountPath(uid, name, &path) != android::OK) {
            return cli->sendMsg(ResponseCode::CommandParameterError,
                                "Invalid mount point name.",
                                false);
        }

        const android::status_t result =
                runCommandInNamespace(command, uid, pid, path, -1 /* device_fd */);
        return sendGenericOkFail(cli, result);
    }

    return cli->sendMsg(ResponseCode::CommandSyntaxError,  "Unknown appfuse cmd", false);
}

android::status_t CommandListener::AppFuseCmd::sendFd(SocketClient *cli, int fd) {
    struct iovec data;
    char dataBuffer[128];
    char controlBuffer[CMSG_SPACE(sizeof(int))];
    struct msghdr message;

    // Message.
    memset(&message, 0, sizeof(struct msghdr));
    message.msg_iov = &data;
    message.msg_iovlen = 1;
    message.msg_control = controlBuffer;
    message.msg_controllen = CMSG_SPACE(sizeof(int));

    // Data.
    data.iov_base = dataBuffer;
    data.iov_len = snprintf(dataBuffer,
                            sizeof(dataBuffer),
                            "200 %d AppFuse command succeeded",
                            cli->getCmdNum()) + 1;

    // Control.
    struct cmsghdr* const controlMessage = CMSG_FIRSTHDR(&message);
    memset(controlBuffer, 0, CMSG_SPACE(sizeof(int)));
    controlMessage->cmsg_level = SOL_SOCKET;
    controlMessage->cmsg_type = SCM_RIGHTS;
    controlMessage->cmsg_len = CMSG_LEN(sizeof(int));
    *((int *) CMSG_DATA(controlMessage)) = fd;

    const int result = TEMP_FAILURE_RETRY(sendmsg(cli->getSocket(), &message, 0));
    if (result == -1) {
        PLOG(ERROR) << "Failed to send FD from vold";
        return -errno;
    }

    return android::OK;
}