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android_system_core/libprocessgroup/processgroup.cpp
Marco Ballesio 4d45b59f80 libprocessgroup: uid/pid hierarchy for cgroup v2 
Enable the uid/pid hierarchy for all groups when using cgroup v2. Mount
the hierarchy under the cgroup v2 root. Make sure that all files under
the hierarchy are accessible by the system user.

Test: booted the device, tested the freezer cgroup, manually verified
the working of the freezer from logs and by checking statuses of
processes.

Bug: 168907513
Test: Booted the device, verified no regressions on process group access
Change-Id: I73f3e767d377902af6e12facb503b9136fb39e08
2020-12-02 09:51:42 -08:00

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16 KiB
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/*
* 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 <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#include <chrono>
#include <map>
#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 <cutils/android_filesystem_config.h>
#include <processgroup/processgroup.h>
#include <task_profiles.h>
using android::base::GetBoolProperty;
using android::base::StartsWith;
using android::base::StringPrintf;
using android::base::WriteStringToFile;
using namespace std::chrono_literals;
#define PROCESSGROUP_CGROUP_PROCS_FILE "/cgroup.procs"
bool CgroupGetControllerPath(const std::string& cgroup_name, std::string* path) {
auto controller = CgroupMap::GetInstance().FindController(cgroup_name);
if (!controller.HasValue()) {
return false;
}
if (path) {
*path = controller.path();
}
return true;
}
bool CgroupGetAttributePath(const std::string& attr_name, std::string* path) {
const TaskProfiles& tp = TaskProfiles::GetInstance();
const ProfileAttribute* attr = tp.GetAttribute(attr_name);
if (attr == nullptr) {
return false;
}
if (path) {
*path = StringPrintf("%s/%s", attr->controller()->path(), attr->file_name().c_str());
}
return true;
}
bool CgroupGetAttributePathForTask(const std::string& attr_name, int tid, std::string* path) {
const TaskProfiles& tp = TaskProfiles::GetInstance();
const ProfileAttribute* attr = tp.GetAttribute(attr_name);
if (attr == nullptr) {
return false;
}
if (!attr->GetPathForTask(tid, path)) {
PLOG(ERROR) << "Failed to find cgroup for tid " << tid;
return false;
}
return true;
}
bool UsePerAppMemcg() {
bool low_ram_device = GetBoolProperty("ro.config.low_ram", false);
return GetBoolProperty("ro.config.per_app_memcg", low_ram_device);
}
static bool isMemoryCgroupSupported() {
static bool memcg_supported = CgroupMap::GetInstance().FindController("memory").IsUsable();
return memcg_supported;
}
void DropTaskProfilesResourceCaching() {
TaskProfiles::GetInstance().DropResourceCaching();
}
bool SetProcessProfiles(uid_t uid, pid_t pid, const std::vector<std::string>& profiles) {
return TaskProfiles::GetInstance().SetProcessProfiles(uid, pid, profiles);
}
bool SetTaskProfiles(int tid, const std::vector<std::string>& profiles, bool use_fd_cache) {
return TaskProfiles::GetInstance().SetTaskProfiles(tid, profiles, use_fd_cache);
}
static std::string ConvertUidToPath(const char* cgroup, uid_t uid) {
return StringPrintf("%s/uid_%d", cgroup, uid);
}
static std::string ConvertUidPidToPath(const char* cgroup, uid_t uid, int pid) {
return StringPrintf("%s/uid_%d/pid_%d", cgroup, uid, pid);
}
static int RemoveProcessGroup(const char* cgroup, uid_t uid, int pid, unsigned int retries) {
int ret = 0;
auto uid_pid_path = ConvertUidPidToPath(cgroup, uid, pid);
auto uid_path = ConvertUidToPath(cgroup, uid);
if (retries == 0) {
retries = 1;
}
while (retries--) {
ret = rmdir(uid_pid_path.c_str());
if (!ret || errno != EBUSY) break;
std::this_thread::sleep_for(5ms);
}
// With the exception of boot or shutdown, system uid_ folders are always populated. Spinning
// here would needlessly delay most pid removals. Additionally, once empty a uid_ cgroup won't
// have processes hanging on it (we've already spun for all its pid_), so there's no need to
// spin anyway.
rmdir(uid_path.c_str());
return ret;
}
static bool RemoveUidProcessGroups(const std::string& uid_path) {
std::unique_ptr<DIR, decltype(&closedir)> uid(opendir(uid_path.c_str()), closedir);
bool empty = true;
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) {
if (errno != EBUSY) {
PLOG(WARNING) << "Failed to remove " << path;
}
empty = false;
}
}
}
return empty;
}
void removeAllProcessGroups() {
LOG(VERBOSE) << "removeAllProcessGroups()";
std::vector<std::string> cgroups;
std::string path;
if (CgroupGetControllerPath(CGROUPV2_CONTROLLER_NAME, &path)) {
cgroups.push_back(path);
}
if (CgroupGetControllerPath("memory", &path)) {
cgroups.push_back(path + "/apps");
}
for (std::string cgroup_root_path : cgroups) {
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);
if (!RemoveUidProcessGroups(path)) {
LOG(VERBOSE) << "Skip removing " << path;
continue;
}
LOG(VERBOSE) << "Removing " << path;
if (rmdir(path.c_str()) == -1 && errno != EBUSY) {
PLOG(WARNING) << "Failed to remove " << path;
}
}
}
}
}
/**
* Process groups are primarily created by the Zygote, meaning that uid/pid groups are created by
* the user root. Ownership for the newly created cgroup and all of its files must thus be
* transferred for the user/group passed as uid/gid before system_server can properly access them.
*/
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;
}
auto dir = std::unique_ptr<DIR, decltype(&closedir)>(opendir(path.c_str()), closedir);
if (dir == NULL) {
PLOG(ERROR) << "opendir failed for " << path;
goto err;
}
struct dirent* dir_entry;
while ((dir_entry = readdir(dir.get()))) {
if (!strcmp("..", dir_entry->d_name)) {
continue;
}
std::string file_path = path + "/" + dir_entry->d_name;
if (lchown(file_path.c_str(), uid, gid) < 0) {
PLOG(ERROR) << "lchown failed for " << file_path;
goto err;
}
if (fchmodat(AT_FDCWD, file_path.c_str(), mode, AT_SYMLINK_NOFOLLOW) != 0) {
PLOG(ERROR) << "fchmodat failed for " << file_path;
goto err;
}
}
return true;
err:
int saved_errno = errno;
rmdir(path.c_str());
errno = saved_errno;
return false;
}
// 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) {
auto path = ConvertUidPidToPath(cgroup, uid, initialPid) + PROCESSGROUP_CGROUP_PROCS_FILE;
std::unique_ptr<FILE, decltype(&fclose)> fd(fopen(path.c_str(), "re"), fclose);
if (!fd) {
if (errno == ENOENT) {
// This happens when process is already dead
return 0;
}
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(*it);
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 && errno != ESRCH) {
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 && errno != ESRCH) {
PLOG(WARNING) << "kill(" << pid << ", " << signal << ") failed";
}
}
return feof(fd.get()) ? processes : -1;
}
static int KillProcessGroup(uid_t uid, int initialPid, int signal, int retries,
int* max_processes) {
std::string hierarchy_root_path;
CgroupGetControllerPath(CGROUPV2_CONTROLLER_NAME, &hierarchy_root_path);
const char* cgroup = hierarchy_root_path.c_str();
std::chrono::steady_clock::time_point start = std::chrono::steady_clock::now();
if (max_processes != nullptr) {
*max_processes = 0;
}
int retry = retries;
int processes;
while ((processes = DoKillProcessGroupOnce(cgroup, uid, initialPid, signal)) > 0) {
if (max_processes != nullptr && processes > *max_processes) {
*max_processes = processes;
}
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";
}
int err = RemoveProcessGroup(cgroup, uid, initialPid, retries);
if (isMemoryCgroupSupported() && UsePerAppMemcg()) {
std::string memory_path;
CgroupGetControllerPath("memory", &memory_path);
memory_path += "/apps";
if (RemoveProcessGroup(memory_path.c_str(), uid, initialPid, retries)) return -1;
}
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, int* max_processes) {
return KillProcessGroup(uid, initialPid, signal, 40 /*retries*/, max_processes);
}
int killProcessGroupOnce(uid_t uid, int initialPid, int signal, int* max_processes) {
return KillProcessGroup(uid, initialPid, signal, 0 /*retries*/, max_processes);
}
static int createProcessGroupInternal(uid_t uid, int initialPid, std::string cgroup) {
auto uid_path = ConvertUidToPath(cgroup.c_str(), 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(cgroup.c_str(), 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;
}
int createProcessGroup(uid_t uid, int initialPid, bool memControl) {
std::string cgroup;
if (memControl && !UsePerAppMemcg()) {
PLOG(ERROR) << "service memory controls are used without per-process memory cgroup support";
return -EINVAL;
}
if (isMemoryCgroupSupported() && UsePerAppMemcg()) {
CgroupGetControllerPath("memory", &cgroup);
cgroup += "/apps";
int ret = createProcessGroupInternal(uid, initialPid, cgroup);
if (ret != 0) {
return ret;
}
}
CgroupGetControllerPath(CGROUPV2_CONTROLLER_NAME, &cgroup);
return createProcessGroupInternal(uid, initialPid, cgroup);
}
static bool SetProcessGroupValue(int tid, const std::string& attr_name, int64_t value) {
if (!isMemoryCgroupSupported()) {
PLOG(ERROR) << "Memcg is not mounted.";
return false;
}
std::string path;
if (!CgroupGetAttributePathForTask(attr_name, tid, &path)) {
PLOG(ERROR) << "Failed to find attribute '" << attr_name << "'";
return false;
}
if (!WriteStringToFile(std::to_string(value), path)) {
PLOG(ERROR) << "Failed to write '" << value << "' to " << path;
return false;
}
return true;
}
bool setProcessGroupSwappiness(uid_t, int pid, int swappiness) {
return SetProcessGroupValue(pid, "MemSwappiness", swappiness);
}
bool setProcessGroupSoftLimit(uid_t, int pid, int64_t soft_limit_in_bytes) {
return SetProcessGroupValue(pid, "MemSoftLimit", soft_limit_in_bytes);
}
bool setProcessGroupLimit(uid_t, int pid, int64_t limit_in_bytes) {
return SetProcessGroupValue(pid, "MemLimit", limit_in_bytes);
}
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