processgroup.cpp

/*
 *  Copyright 2014 Google, Inc
 *
 *  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.
 */

//#define LOG_NDEBUG 0
#define LOG_TAG "libprocessgroup"

#include <assert.h>
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <inttypes.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

#include <chrono>
#include <memory>
#include <mutex>
#include <set>
#include <string>
#include <thread>

#include <android-base/file.h>
#include <android-base/logging.h>
#include <android-base/properties.h>
#include <android-base/stringprintf.h>
#include <android-base/strings.h>
#include <private/android_filesystem_config.h>

#include <processgroup/processgroup.h>

using android::base::GetBoolProperty;
using android::base::StartsWith;
using android::base::StringPrintf;
using android::base::WriteStringToFile;

using namespace std::chrono_literals;

#define MEM_CGROUP_PATH "/dev/memcg/apps"
#define MEM_CGROUP_TASKS "/dev/memcg/apps/tasks"
#define ACCT_CGROUP_PATH "/acct"

#define PROCESSGROUP_CGROUP_PROCS_FILE "/cgroup.procs"

std::once_flag init_path_flag;

static const std::string& GetCgroupRootPath() {
    static std::string cgroup_root_path;
    std::call_once(init_path_flag, [&]() {
        // low-ram devices use per-app memcg by default, unlike high-end ones
        bool low_ram_device = GetBoolProperty("ro.config.low_ram", false);
        bool per_app_memcg =
            GetBoolProperty("ro.config.per_app_memcg", low_ram_device);
        if (per_app_memcg) {
            // Check if mem cgroup is mounted, only then check for
            // write-access to avoid SELinux denials
            cgroup_root_path =
                (access(MEM_CGROUP_TASKS, F_OK) || access(MEM_CGROUP_PATH, W_OK) ?
                ACCT_CGROUP_PATH : MEM_CGROUP_PATH);
        } else {
            cgroup_root_path = ACCT_CGROUP_PATH;
        }
    });
    return cgroup_root_path;
}

static std::string ConvertUidToPath(uid_t uid) {
    return StringPrintf("%s/uid_%d", GetCgroupRootPath().c_str(), uid);
}

static std::string ConvertUidPidToPath(uid_t uid, int pid) {
    return StringPrintf("%s/uid_%d/pid_%d", GetCgroupRootPath().c_str(), uid, pid);
}

static int RemoveProcessGroup(uid_t uid, int pid) {
    int ret;

    auto uid_pid_path = ConvertUidPidToPath(uid, pid);
    ret = rmdir(uid_pid_path.c_str());

    auto uid_path = ConvertUidToPath(uid);
    rmdir(uid_path.c_str());

    return ret;
}

static void RemoveUidProcessGroups(const std::string& uid_path) {
    std::unique_ptr<DIR, decltype(&closedir)> uid(opendir(uid_path.c_str()), closedir);
    if (uid != NULL) {
        dirent* dir;
        while ((dir = readdir(uid.get())) != nullptr) {
            if (dir->d_type != DT_DIR) {
                continue;
            }

            if (!StartsWith(dir->d_name, "pid_")) {
                continue;
            }

            auto path = StringPrintf("%s/%s", uid_path.c_str(), dir->d_name);
            LOG(VERBOSE) << "Removing " << path;
            if (rmdir(path.c_str()) == -1) PLOG(WARNING) << "Failed to remove " << path;
        }
    }
}

void removeAllProcessGroups()
{
    LOG(VERBOSE) << "removeAllProcessGroups()";
    const auto& cgroup_root_path = GetCgroupRootPath();
    std::unique_ptr<DIR, decltype(&closedir)> root(opendir(cgroup_root_path.c_str()), closedir);
    if (root == NULL) {
        PLOG(ERROR) << "Failed to open " << cgroup_root_path;
    } else {
        dirent* dir;
        while ((dir = readdir(root.get())) != nullptr) {
            if (dir->d_type != DT_DIR) {
                continue;
            }

            if (!StartsWith(dir->d_name, "uid_")) {
                continue;
            }

            auto path = StringPrintf("%s/%s", cgroup_root_path.c_str(), dir->d_name);
            RemoveUidProcessGroups(path);
            LOG(VERBOSE) << "Removing " << path;
            if (rmdir(path.c_str()) == -1) PLOG(WARNING) << "Failed to remove " << path;
        }
    }
}

// Returns number of processes killed on success
// Returns 0 if there are no processes in the process cgroup left to kill
// Returns -1 on error
static int DoKillProcessGroupOnce(uid_t uid, int initialPid, int signal) {
    auto path = ConvertUidPidToPath(uid, initialPid) + PROCESSGROUP_CGROUP_PROCS_FILE;
    std::unique_ptr<FILE, decltype(&fclose)> fd(fopen(path.c_str(), "re"), fclose);
    if (!fd) {
        PLOG(WARNING) << "Failed to open process cgroup uid " << uid << " pid " << initialPid;
        return -1;
    }

    // We separate all of the pids in the cgroup into those pids that are also the leaders of
    // process groups (stored in the pgids set) and those that are not (stored in the pids set).
    std::set<pid_t> pgids;
    pgids.emplace(initialPid);
    std::set<pid_t> pids;

    pid_t pid;
    int processes = 0;
    while (fscanf(fd.get(), "%d\n", &pid) == 1 && pid >= 0) {
        processes++;
        if (pid == 0) {
            // Should never happen...  but if it does, trying to kill this
            // will boomerang right back and kill us!  Let's not let that happen.
            LOG(WARNING) << "Yikes, we've been told to kill pid 0!  How about we don't do that?";
            continue;
        }
        pid_t pgid = getpgid(pid);
        if (pgid == -1) PLOG(ERROR) << "getpgid(" << pid << ") failed";
        if (pgid == pid) {
            pgids.emplace(pid);
        } else {
            pids.emplace(pid);
        }
    }

    // Erase all pids that will be killed when we kill the process groups.
    for (auto it = pids.begin(); it != pids.end();) {
        pid_t pgid = getpgid(pid);
        if (pgids.count(pgid) == 1) {
            it = pids.erase(it);
        } else {
            ++it;
        }
    }

    // Kill all process groups.
    for (const auto pgid : pgids) {
        LOG(VERBOSE) << "Killing process group " << -pgid << " in uid " << uid
                     << " as part of process cgroup " << initialPid;

        if (kill(-pgid, signal) == -1) {
            PLOG(WARNING) << "kill(" << -pgid << ", " << signal << ") failed";
        }
    }

    // Kill remaining pids.
    for (const auto pid : pids) {
        LOG(VERBOSE) << "Killing pid " << pid << " in uid " << uid << " as part of process cgroup "
                     << initialPid;

        if (kill(pid, signal) == -1) {
            PLOG(WARNING) << "kill(" << pid << ", " << signal << ") failed";
        }
    }

    return feof(fd.get()) ? processes : -1;
}

static int KillProcessGroup(uid_t uid, int initialPid, int signal, int retries) {
    std::chrono::steady_clock::time_point start = std::chrono::steady_clock::now();

    int retry = retries;
    int processes;
    while ((processes = DoKillProcessGroupOnce(uid, initialPid, signal)) > 0) {
        LOG(VERBOSE) << "Killed " << processes << " processes for processgroup " << initialPid;
        if (retry > 0) {
            std::this_thread::sleep_for(5ms);
            --retry;
        } else {
            break;
        }
    }

    if (processes < 0) {
        PLOG(ERROR) << "Error encountered killing process cgroup uid " << uid << " pid "
                    << initialPid;
        return -1;
    }

    std::chrono::steady_clock::time_point end = std::chrono::steady_clock::now();
    auto ms = std::chrono::duration_cast<std::chrono::milliseconds>(end - start).count();

    // We only calculate the number of 'processes' when killing the processes.
    // In the retries == 0 case, we only kill the processes once and therefore
    // will not have waited then recalculated how many processes are remaining
    // after the first signals have been sent.
    // Logging anything regarding the number of 'processes' here does not make sense.

    if (processes == 0) {
        if (retries > 0) {
            LOG(INFO) << "Successfully killed process cgroup uid " << uid << " pid " << initialPid
                      << " in " << static_cast<int>(ms) << "ms";
        }
        return RemoveProcessGroup(uid, initialPid);
    } else {
        if (retries > 0) {
            LOG(ERROR) << "Failed to kill process cgroup uid " << uid << " pid " << initialPid
                       << " in " << static_cast<int>(ms) << "ms, " << processes
                       << " processes remain";
        }
        return -1;
    }
}

int killProcessGroup(uid_t uid, int initialPid, int signal) {
    return KillProcessGroup(uid, initialPid, signal, 40 /*retries*/);
}

int killProcessGroupOnce(uid_t uid, int initialPid, int signal) {
    return KillProcessGroup(uid, initialPid, signal, 0 /*retries*/);
}

static bool MkdirAndChown(const std::string& path, mode_t mode, uid_t uid, gid_t gid) {
    if (mkdir(path.c_str(), mode) == -1 && errno != EEXIST) {
        return false;
    }

    if (chown(path.c_str(), uid, gid) == -1) {
        int saved_errno = errno;
        rmdir(path.c_str());
        errno = saved_errno;
        return false;
    }

    return true;
}

int createProcessGroup(uid_t uid, int initialPid)
{
    auto uid_path = ConvertUidToPath(uid);

    if (!MkdirAndChown(uid_path, 0750, AID_SYSTEM, AID_SYSTEM)) {
        PLOG(ERROR) << "Failed to make and chown " << uid_path;
        return -errno;
    }

    auto uid_pid_path = ConvertUidPidToPath(uid, initialPid);

    if (!MkdirAndChown(uid_pid_path, 0750, AID_SYSTEM, AID_SYSTEM)) {
        PLOG(ERROR) << "Failed to make and chown " << uid_pid_path;
        return -errno;
    }

    auto uid_pid_procs_file = uid_pid_path + PROCESSGROUP_CGROUP_PROCS_FILE;

    int ret = 0;
    if (!WriteStringToFile(std::to_string(initialPid), uid_pid_procs_file)) {
        ret = -errno;
        PLOG(ERROR) << "Failed to write '" << initialPid << "' to " << uid_pid_procs_file;
    }

    return ret;
}

static bool SetProcessGroupValue(uid_t uid, int pid, const std::string& file_name, int64_t value) {
    if (GetCgroupRootPath() != MEM_CGROUP_PATH) {
        PLOG(ERROR) << "Memcg is not mounted.";
        return false;
    }

    auto path = ConvertUidPidToPath(uid, pid) + file_name;

    if (!WriteStringToFile(std::to_string(value), path)) {
        PLOG(ERROR) << "Failed to write '" << value << "' to " << path;
        return false;
    }
    return true;
}

bool setProcessGroupSwappiness(uid_t uid, int pid, int swappiness) {
    return SetProcessGroupValue(uid, pid, "/memory.swappiness", swappiness);
}

bool setProcessGroupSoftLimit(uid_t uid, int pid, int64_t soft_limit_in_bytes) {
    return SetProcessGroupValue(uid, pid, "/memory.soft_limit_in_bytes", soft_limit_in_bytes);
}

bool setProcessGroupLimit(uid_t uid, int pid, int64_t limit_in_bytes) {
    return SetProcessGroupValue(uid, pid, "/memory.limit_in_bytes", limit_in_bytes);
}