Magisk/native/jni/su/su_daemon.cpp

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#include <unistd.h>
#include <pthread.h>
#include <stdlib.h>
#include <fcntl.h>
#include <string.h>
#include <signal.h>
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#include <pwd.h>
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#include <time.h>
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#include <sys/socket.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>
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#include <sys/mount.h>
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#include <logging.h>
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#include <daemon.h>
#include <utils.h>
#include <selinux.h>
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#include "su.h"
#include "pts.h"
#define LOCK_CACHE() pthread_mutex_lock(&cache_lock)
#define UNLOCK_CACHE() pthread_mutex_unlock(&cache_lock)
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static pthread_mutex_t cache_lock = PTHREAD_MUTEX_INITIALIZER;
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static su_info *cache;
su_info::su_info(unsigned uid) :
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uid(uid), count(0), access(DEFAULT_SU_ACCESS), mgr_st({}), ref(0),
timestamp(0), _lock(PTHREAD_MUTEX_INITIALIZER) {}
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su_info::~su_info() {
pthread_mutex_destroy(&_lock);
}
void su_info::lock() {
pthread_mutex_lock(&_lock);
}
void su_info::unlock() {
pthread_mutex_unlock(&_lock);
}
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bool su_info::isFresh() {
return time(nullptr) - timestamp < 3; /* 3 seconds */
}
void su_info::newRef() {
timestamp = time(nullptr);
++ref;
}
void su_info::deRef() {
LOCK_CACHE();
--ref;
if (ref == 0 && !isFresh()) {
if (cache == this)
cache = nullptr;
delete this;
}
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UNLOCK_CACHE();
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}
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static void database_check(su_info *info) {
int uid = info->uid;
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get_db_settings(info->cfg);
get_db_strings(info->str);
// Check multiuser settings
switch (info->cfg[SU_MULTIUSER_MODE]) {
case MULTIUSER_MODE_OWNER_ONLY:
if (info->uid / 100000) {
uid = -1;
info->access = NO_SU_ACCESS;
}
break;
case MULTIUSER_MODE_OWNER_MANAGED:
uid = info->uid % 100000;
break;
case MULTIUSER_MODE_USER:
default:
break;
}
if (uid > 0)
get_uid_policy(info->access, uid);
// We need to check our manager
if (info->access.log || info->access.notify)
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validate_manager(info->str[SU_MANAGER], uid / 100000, &info->mgr_st);
}
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static su_info *get_su_info(unsigned uid) {
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su_info *info = nullptr;
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// Get from cache or new instance
LOCK_CACHE();
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if (cache && cache->uid == uid && cache->isFresh()) {
info = cache;
} else {
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if (cache && cache->ref == 0)
delete cache;
cache = info = new su_info(uid);
}
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info->newRef();
UNLOCK_CACHE();
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LOGD("su: request from uid=[%d] (#%d)\n", info->uid, ++info->count);
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// Lock before the policy is determined
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info->lock();
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if (info->access.policy == QUERY) {
// Not cached, get data from database
database_check(info);
// Check su access settings
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switch (info->cfg[ROOT_ACCESS]) {
case ROOT_ACCESS_DISABLED:
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LOGW("Root access is disabled!\n");
info->access = NO_SU_ACCESS;
break;
case ROOT_ACCESS_ADB_ONLY:
if (info->uid != UID_SHELL) {
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LOGW("Root access limited to ADB only!\n");
info->access = NO_SU_ACCESS;
}
break;
case ROOT_ACCESS_APPS_ONLY:
if (info->uid == UID_SHELL) {
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LOGW("Root access is disabled for ADB!\n");
info->access = NO_SU_ACCESS;
}
break;
case ROOT_ACCESS_APPS_AND_ADB:
default:
break;
}
// If it's the manager, allow it silently
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if ((info->uid % 100000) == (info->mgr_st.st_uid % 100000))
info->access = SILENT_SU_ACCESS;
// Allow if it's root
if (info->uid == UID_ROOT)
info->access = SILENT_SU_ACCESS;
// If still not determined, check if manager exists
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if (info->access.policy == QUERY && info->str[SU_MANAGER][0] == '\0')
info->access = NO_SU_ACCESS;
}
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// If still not determined, ask manager
if (info->access.policy == QUERY) {
// Create random socket
struct sockaddr_un addr;
int sockfd = create_rand_socket(&addr);
// Connect manager
app_connect(addr.sun_path + 1, info);
int fd = socket_accept(sockfd, 60);
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if (fd < 0) {
info->access.policy = DENY;
} else {
socket_send_request(fd, info);
int ret = read_int_be(fd);
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info->access.policy = ret < 0 ? DENY : static_cast<policy_t>(ret);
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close(fd);
}
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close(sockfd);
}
// Unlock
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info->unlock();
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return info;
}
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static void set_identity(unsigned uid) {
/*
* Set effective uid back to root, otherwise setres[ug]id will fail
* if uid isn't root.
*/
if (seteuid(0)) {
PLOGE("seteuid (root)");
}
if (setresgid(uid, uid, uid)) {
PLOGE("setresgid (%u)", uid);
}
if (setresuid(uid, uid, uid)) {
PLOGE("setresuid (%u)", uid);
}
}
void su_daemon_handler(int client, struct ucred *credential) {
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LOGD("su: request from pid=[%d], client=[%d]\n", credential->pid, client);
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su_info *info = get_su_info(credential->uid);
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// Fail fast
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if (info->access.policy == DENY && info->str[SU_MANAGER][0] == '\0') {
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LOGD("su: fast deny\n");
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info->deRef();
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write_int(client, DENY);
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close(client);
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return;
}
/* Fork a new process, the child process will need to setsid,
* open a pseudo-terminal if needed, and will eventually run exec
* The parent process will wait for the result and
* send the return code back to our client
*/
int child = xfork();
if (child) {
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info->deRef();
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// Wait result
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LOGD("su: waiting child pid=[%d]\n", child);
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int status, code;
if (waitpid(child, &status, 0) > 0)
code = WEXITSTATUS(status);
else
code = -1;
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LOGD("su: return code=[%d]\n", code);
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write(client, &code, sizeof(code));
close(client);
return;
}
LOGD("su: fork handler\n");
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// Abort upon any error occurred
log_cb.ex = exit;
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su_context ctx = {
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.info = info,
.pid = credential->pid
};
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// ack
write_int(client, 0);
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// Become session leader
xsetsid();
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// Read su_request
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xxread(client, &ctx.req, sizeof(su_req_base));
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ctx.req.shell = read_string(client);
ctx.req.command = read_string(client);
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// Get pts_slave
char *pts_slave = read_string(client);
// The FDs for each of the streams
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int infd = recv_fd(client);
int outfd = recv_fd(client);
int errfd = recv_fd(client);
if (pts_slave[0]) {
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LOGD("su: pts_slave=[%s]\n", pts_slave);
// Check pts_slave file is owned by daemon_from_uid
struct stat st;
xstat(pts_slave, &st);
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// If caller is not root, ensure the owner of pts_slave is the caller
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if(st.st_uid != info->uid && info->uid != 0)
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LOGE("su: Wrong permission of pts_slave");
// Opening the TTY has to occur after the
// fork() and setsid() so that it becomes
// our controlling TTY and not the daemon's
int ptsfd = xopen(pts_slave, O_RDWR);
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if (infd < 0)
infd = ptsfd;
if (outfd < 0)
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outfd = ptsfd;
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if (errfd < 0)
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errfd = ptsfd;
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}
free(pts_slave);
// Swap out stdin, stdout, stderr
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xdup2(infd, STDIN_FILENO);
xdup2(outfd, STDOUT_FILENO);
xdup2(errfd, STDERR_FILENO);
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// Unleash all streams from SELinux hell
setfilecon("/proc/self/fd/0", "u:object_r:" SEPOL_FILE_DOMAIN ":s0");
setfilecon("/proc/self/fd/1", "u:object_r:" SEPOL_FILE_DOMAIN ":s0");
setfilecon("/proc/self/fd/2", "u:object_r:" SEPOL_FILE_DOMAIN ":s0");
close(infd);
close(outfd);
close(errfd);
close(client);
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// Handle namespaces
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if (ctx.req.mount_master)
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info->cfg[SU_MNT_NS] = NAMESPACE_MODE_GLOBAL;
switch (info->cfg[SU_MNT_NS]) {
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case NAMESPACE_MODE_GLOBAL:
LOGD("su: use global namespace\n");
break;
case NAMESPACE_MODE_REQUESTER:
LOGD("su: use namespace of pid=[%d]\n", ctx.pid);
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if (switch_mnt_ns(ctx.pid))
LOGD("su: setns failed, fallback to global\n");
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break;
case NAMESPACE_MODE_ISOLATE:
LOGD("su: use new isolated namespace\n");
xunshare(CLONE_NEWNS);
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xmount(nullptr, "/", nullptr, MS_PRIVATE | MS_REC, nullptr);
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break;
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}
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if (info->access.log)
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app_log(&ctx);
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else if (info->access.notify)
app_notify(&ctx);
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if (info->access.policy == ALLOW) {
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const char *argv[] = { nullptr, nullptr, nullptr, nullptr };
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argv[0] = ctx.req.login ? "-" : ctx.req.shell;
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if (ctx.req.command[0]) {
argv[1] = "-c";
argv[2] = ctx.req.command;
}
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// Setup environment
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umask(022);
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char path[32], buf[4096];
snprintf(path, sizeof(path), "/proc/%d/cwd", ctx.pid);
xreadlink(path, buf, sizeof(buf));
chdir(buf);
snprintf(path, sizeof(path), "/proc/%d/environ", ctx.pid);
memset(buf, 0, sizeof(buf));
int fd = open(path, O_RDONLY);
read(fd, buf, sizeof(buf));
close(fd);
clearenv();
for (size_t pos = 0; buf[pos];) {
putenv(buf + pos);
pos += strlen(buf + pos) + 1;
}
if (!ctx.req.keepenv) {
struct passwd *pw;
pw = getpwuid(ctx.req.uid);
if (pw) {
setenv("HOME", pw->pw_dir, 1);
if (ctx.req.login || ctx.req.uid) {
setenv("USER", pw->pw_name, 1);
setenv("LOGNAME", pw->pw_name, 1);
}
setenv("SHELL", ctx.req.shell, 1);
}
}
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set_identity(ctx.req.uid);
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execvp(ctx.req.shell, (char **) argv);
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fprintf(stderr, "Cannot execute %s: %s\n", ctx.req.shell, strerror(errno));
PLOGE("exec");
exit(EXIT_FAILURE);
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} else {
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LOGW("su: request rejected (%u->%u)", info->uid, ctx.req.uid);
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fprintf(stderr, "%s\n", strerror(EACCES));
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exit(EXIT_FAILURE);
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}
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}