Revert "libprocessgroup: Poll on cgroup.events"

// should be active again. E.g. Zygote specialization for child process.

void DropTaskProfilesResourceCaching();

// Return 0 if all processes were killed and the cgroup was successfully removed.

// Returns -1 in the case of an error occurring or if there are processes still running.

// Return 0 and removes the cgroup if there are no longer any processes in it.

// Returns -1 in the case of an error occurring or if there are processes still running

// even after retrying for up to 200ms.

int killProcessGroup(uid_t uid, int initialPid, int signal);

// Returns the same as killProcessGroup(), however it does not retry, which means

// Sends the provided signal to all members of a process group, but does not wait for processes to

// exit, or for the cgroup to be removed. Callers should also ensure that killProcessGroup is called

// later to ensure the cgroup is fully removed, otherwise system resources will leak.

// Returns true if no errors are encountered sending signals, otherwise false.

bool sendSignalToProcessGroup(uid_t uid, int initialPid, int signal);

// later to ensure the cgroup is fully removed, otherwise system resources may leak.

int sendSignalToProcessGroup(uid_t uid, int initialPid, int signal);

int createProcessGroup(uid_t uid, int initialPid, bool memControl = false);

#include <errno.h>

#include <fcntl.h>

#include <inttypes.h>

#include <poll.h>

#include <signal.h>

#include <stdio.h>

#include <stdlib.h>

#include <unistd.h>

#include <chrono>

#include <cstring>

#include <map>

#include <memory>

#include <mutex>

using namespace std::chrono_literals;

#define PROCESSGROUP_CGROUP_PROCS_FILE "cgroup.procs"

#define PROCESSGROUP_CGROUP_EVENTS_FILE "cgroup.events"

#define PROCESSGROUP_CGROUP_PROCS_FILE "/cgroup.procs"

bool CgroupsAvailable() {

    static bool cgroups_available = access("/proc/cgroups", F_OK) == 0;

    return StringPrintf("%s/uid_%u/pid_%d", cgroup, uid, pid);

}

static int RemoveCgroup(const char* cgroup, uid_t uid, int pid) {

    auto path = ConvertUidPidToPath(cgroup, uid, pid);

    int ret = TEMP_FAILURE_RETRY(rmdir(path.c_str()));

static int RemoveCgroup(const char* cgroup, uid_t uid, int pid, unsigned int retries) {

    int ret = 0;

    auto uid_pid_path = ConvertUidPidToPath(cgroup, uid, pid);

    while (retries--) {

        ret = rmdir(uid_pid_path.c_str());

        // If we get an error 2 'No such file or directory' , that means the

        // cgroup is already removed, treat it as success and return 0 for

        // idempotency.

        if (ret < 0 && errno == ENOENT) {

            ret = 0;

        }

        if (!ret || errno != EBUSY || !retries) break;

        std::this_thread::sleep_for(5ms);

    }

    if (!ret && uid >= AID_ISOLATED_START && uid <= AID_ISOLATED_END) {

        // Isolated UIDs are unlikely to be reused soon after removal,

        // so free up the kernel resources for the UID level cgroup.

        path = ConvertUidToPath(cgroup, uid);

        ret = TEMP_FAILURE_RETRY(rmdir(path.c_str()));

    }

        const auto uid_path = ConvertUidToPath(cgroup, uid);

        ret = rmdir(uid_path.c_str());

        if (ret < 0 && errno == ENOENT) {

        // This function is idempoetent, but still warn here.

        LOG(WARNING) << "RemoveCgroup: " << path << " does not exist.";

            ret = 0;

        }

    }

    return ret;

}

    return false;

}

bool sendSignalToProcessGroup(uid_t uid, int initialPid, int signal) {

    std::set<pid_t> pgids, pids;

    if (CgroupsAvailable()) {

        std::string hierarchy_root_path, cgroup_v2_path;

        CgroupGetControllerPath(CGROUPV2_HIERARCHY_NAME, &hierarchy_root_path);

        cgroup_v2_path = ConvertUidPidToPath(hierarchy_root_path.c_str(), uid, initialPid);

        LOG(VERBOSE) << "Using " << PROCESSGROUP_CGROUP_PROCS_FILE << " to signal (" << signal

                     << ") " << cgroup_v2_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(const char* cgroup, uid_t uid, int initialPid, int signal) {

    // 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).

        const auto procsfilepath = cgroup_v2_path + '/' + PROCESSGROUP_CGROUP_PROCS_FILE;

        std::unique_ptr<FILE, decltype(&fclose)> fp(fopen(procsfilepath.c_str(), "re"), fclose);

        if (!fp) {

            // This should only happen if the cgroup has already been removed with a successful call

            // to killProcessGroup. Callers should only retry sendSignalToProcessGroup or

            // killProcessGroup calls if they fail without ENOENT.

            PLOG(ERROR) << "Failed to open " << procsfilepath;

            kill(-initialPid, signal);

            return false;

        }

    std::set<pid_t> pgids;

    pgids.emplace(initialPid);

    std::set<pid_t> pids;

    int processes = 0;

    std::unique_ptr<FILE, decltype(&fclose)> fd(nullptr, fclose);

    if (CgroupsAvailable()) {

        auto path = ConvertUidPidToPath(cgroup, uid, initialPid) + PROCESSGROUP_CGROUP_PROCS_FILE;

        fd.reset(fopen(path.c_str(), "re"));

        if (!fd) {

            if (errno == ENOENT) {

                // This happens when the process is already dead or if, as the result of a bug, it

                // has been migrated to another cgroup. An example of a bug that can cause migration

                // to another cgroup is using the JoinCgroup action with a cgroup controller that

                // has been activated in the v2 cgroup hierarchy.

                goto kill;

            }

            PLOG(WARNING) << __func__ << " failed to open process cgroup uid " << uid << " pid "

                          << initialPid;

            return -1;

        }

        pid_t pid;

        bool file_is_empty = true;

        while (fscanf(fp.get(), "%d\n", &pid) == 1 && pid >= 0) {

        while (fscanf(fd.get(), "%d\n", &pid) == 1 && pid >= 0) {

            processes++;

            file_is_empty = false;

            if (pid == 0) {

                // Should never happen...  but if it does, trying to kill this

        }

    }

    pgids.emplace(initialPid);

kill:

    // Kill all process groups.

    for (const auto pgid : pgids) {

        LOG(VERBOSE) << "Killing process group " << -pgid << " in uid " << uid

        }

    }

    return true;

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

}

template <typename T>

static std::chrono::milliseconds toMillisec(T&& duration) {

    return std::chrono::duration_cast<std::chrono::milliseconds>(duration);

}

enum class populated_status

{

    populated,

    not_populated,

    error

};

static populated_status cgroupIsPopulated(int events_fd) {

    const std::string POPULATED_KEY("populated ");

    const std::string::size_type MAX_EVENTS_FILE_SIZE = 32;

    std::string buf;

    buf.resize(MAX_EVENTS_FILE_SIZE);

    ssize_t len = TEMP_FAILURE_RETRY(pread(events_fd, buf.data(), buf.size(), 0));

    if (len == -1) {

        PLOG(ERROR) << "Could not read cgroup.events: ";

        // Potentially ENODEV if the cgroup has been removed since we opened this file, but that

        // shouldn't have happened yet.

        return populated_status::error;

    }

    if (len == 0) {

        LOG(ERROR) << "cgroup.events EOF";

        return populated_status::error;

    }

    buf.resize(len);

    const std::string::size_type pos = buf.find(POPULATED_KEY);

    if (pos == std::string::npos) {

        LOG(ERROR) << "Could not find populated key in cgroup.events";

        return populated_status::error;

    }

    if (pos + POPULATED_KEY.size() + 1 > len) {

        LOG(ERROR) << "Partial read of cgroup.events";

        return populated_status::error;

    }

    return buf[pos + POPULATED_KEY.size()] == '1' ?

        populated_status::populated : populated_status::not_populated;

}

// The default timeout of 2200ms comes from the default number of retries in a previous

// implementation of this function. The default retry value was 40 for killing and 400 for cgroup

// removal with 5ms sleeps between each retry.

static int KillProcessGroup(

        uid_t uid, int initialPid, int signal, bool once = false,

        std::chrono::steady_clock::time_point until = std::chrono::steady_clock::now() + 2200ms) {

static int KillProcessGroup(uid_t uid, int initialPid, int signal, int retries) {

    CHECK_GE(uid, 0);

    CHECK_GT(initialPid, 0);

    // Always attempt to send a kill signal to at least the initialPid, at least once, regardless of

    // whether its cgroup exists or not. This should only be necessary if a bug results in the

    // migration of the targeted process out of its cgroup, which we will also attempt to kill.

    const bool signal_ret = sendSignalToProcessGroup(uid, initialPid, signal);

    if (!CgroupsAvailable() || !signal_ret) return signal_ret ? 0 : -1;

    std::string hierarchy_root_path;

    if (CgroupsAvailable()) {

        CgroupGetControllerPath(CGROUPV2_HIERARCHY_NAME, &hierarchy_root_path);

    }

    const char* cgroup = hierarchy_root_path.c_str();

    const std::string cgroup_v2_path =

            ConvertUidPidToPath(hierarchy_root_path.c_str(), uid, initialPid);

    std::chrono::steady_clock::time_point start = std::chrono::steady_clock::now();

    const std::string eventsfile = cgroup_v2_path + '/' + PROCESSGROUP_CGROUP_EVENTS_FILE;

    android::base::unique_fd events_fd(open(eventsfile.c_str(), O_RDONLY));

    if (events_fd.get() == -1) {

        PLOG(WARNING) << "Error opening " << eventsfile << " for KillProcessGroup";

        return -1;

    int retry = retries;

    int processes;

    while ((processes = DoKillProcessGroupOnce(cgroup, uid, initialPid, signal)) > 0) {

        LOG(VERBOSE) << "Killed " << processes << " processes for processgroup " << initialPid;

        if (!CgroupsAvailable()) {

            // makes no sense to retry, because there are no cgroup_procs file

            processes = 0;  // no remaining processes

            break;

        }

    struct pollfd fds = {

        .fd = events_fd,

        .events = POLLPRI,

    };

    const std::chrono::steady_clock::time_point start = std::chrono::steady_clock::now();

    // The primary reason to loop here is to capture any new forks or migrations that could occur

    // after we send signals to the original set of processes, but before all of those processes

    // exit and the cgroup becomes unpopulated, or before we remove the cgroup. We try hard to

    // ensure this completes successfully to avoid permanent memory leaks, but we still place a

    // large default upper bound on the amount of time we spend in this loop. The amount of CPU

    // contention, and the amount of work that needs to be done in do_exit for each process

    // determines how long this will take.

    int ret;

    do {

        populated_status populated;

        while ((populated = cgroupIsPopulated(events_fd.get())) == populated_status::populated &&

               std::chrono::steady_clock::now() < until) {

            sendSignalToProcessGroup(uid, initialPid, signal);

            if (once) {

                populated = cgroupIsPopulated(events_fd.get());

        if (retry > 0) {

            std::this_thread::sleep_for(5ms);

            --retry;

        } else {

            break;

        }

    }

            const std::chrono::steady_clock::time_point poll_start =

                    std::chrono::steady_clock::now();

    if (processes < 0) {

        PLOG(ERROR) << "Error encountered killing process cgroup uid " << uid << " pid "

                    << initialPid;

        return -1;

    }

            if (poll_start < until)

                ret = TEMP_FAILURE_RETRY(poll(&fds, 1, toMillisec(until - poll_start).count()));

    std::chrono::steady_clock::time_point end = std::chrono::steady_clock::now();

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

            if (ret == -1) {

                // Fallback to 5ms sleeps if poll fails

                PLOG(ERROR) << "Poll on " << eventsfile << "failed";

                const std::chrono::steady_clock::time_point now = std::chrono::steady_clock::now();

                if (now < until)

                    std::this_thread::sleep_for(std::min(5ms, toMillisec(until - now)));

            }

    // 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.

            LOG(VERBOSE) << "Waited "

                         << toMillisec(std::chrono::steady_clock::now() - poll_start).count()

                         << " ms for " << eventsfile << " poll";

    if (processes == 0) {

        if (retries > 0) {

            LOG(INFO) << "Successfully killed process cgroup uid " << uid << " pid " << initialPid

                      << " in " << static_cast<int>(ms) << "ms";

        }

        const std::chrono::milliseconds kill_duration =

                toMillisec(std::chrono::steady_clock::now() - start);

        if (populated == populated_status::populated) {

            LOG(WARNING) << "Still waiting on process(es) to exit for cgroup " << cgroup_v2_path

                         << " after " << kill_duration.count() << " ms";

            // We'll still try the cgroup removal below which we expect to log an error.

        } else if (populated == populated_status::not_populated) {

            LOG(VERBOSE) << "Killed all processes under cgroup " << cgroup_v2_path

                         << " after " << kill_duration.count() << " ms";

        if (!CgroupsAvailable()) {

            // nothing to do here, if cgroups isn't available

            return 0;

        }

        ret = RemoveCgroup(hierarchy_root_path.c_str(), uid, initialPid);

        if (ret)

            PLOG(ERROR) << "Unable to remove cgroup " << cgroup_v2_path;

        else

            LOG(INFO) << "Removed cgroup " << cgroup_v2_path;

        // 400 retries correspond to 2 secs max timeout

        int err = RemoveCgroup(cgroup, uid, initialPid, 400);

        if (isMemoryCgroupSupported() && UsePerAppMemcg()) {

            // This per-application memcg v1 case should eventually be removed after migration to

            // memcg v2.

            std::string memcg_apps_path;

            if (CgroupGetMemcgAppsPath(&memcg_apps_path) &&

                (ret = RemoveCgroup(memcg_apps_path.c_str(), uid, initialPid)) < 0) {

                const auto memcg_v1_cgroup_path =

                        ConvertUidPidToPath(memcg_apps_path.c_str(), uid, initialPid);

                PLOG(ERROR) << "Unable to remove memcg v1 cgroup " << memcg_v1_cgroup_path;

                RemoveCgroup(memcg_apps_path.c_str(), uid, initialPid, 400) < 0) {

                return -1;

            }

        }

        if (once) break;

        if (std::chrono::steady_clock::now() >= until) break;

    } while (ret && errno == EBUSY);

    return ret;

        return err;

    } 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);

    return KillProcessGroup(uid, initialPid, signal, 40 /*retries*/);

}

int killProcessGroupOnce(uid_t uid, int initialPid, int signal) {

    return KillProcessGroup(uid, initialPid, signal, true);

    return KillProcessGroup(uid, initialPid, signal, 0 /*retries*/);

}

int sendSignalToProcessGroup(uid_t uid, int initialPid, int signal) {

    std::string hierarchy_root_path;

    if (CgroupsAvailable()) {

        CgroupGetControllerPath(CGROUPV2_HIERARCHY_NAME, &hierarchy_root_path);

    }

    const char* cgroup = hierarchy_root_path.c_str();

    return DoKillProcessGroupOnce(cgroup, uid, initialPid, signal);

}

static int createProcessGroupInternal(uid_t uid, int initialPid, std::string cgroup,

        return -errno;

    }

    auto uid_pid_procs_file = uid_pid_path + '/' + PROCESSGROUP_CGROUP_PROCS_FILE;

    auto uid_pid_procs_file = uid_pid_path + PROCESSGROUP_CGROUP_PROCS_FILE;

    if (!WriteStringToFile(std::to_string(initialPid), uid_pid_procs_file)) {

        ret = -errno;