Magisk/native/jni/su/su_daemon.cpp

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#include <unistd.h>
#include <fcntl.h>
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#include <pwd.h>
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#include <sys/socket.h>
#include <sys/wait.h>
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#include <sys/mount.h>
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#include <daemon.hpp>
#include <utils.hpp>
#include <selinux.hpp>
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#include <db.hpp>
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#include "su.hpp"
#include "pts.hpp"
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using namespace std;
static pthread_mutex_t cache_lock = PTHREAD_MUTEX_INITIALIZER;
static shared_ptr<su_info> cached;
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su_info::su_info(unsigned uid) :
uid(uid), access(DEFAULT_SU_ACCESS), mgr_st({}),
timestamp(0), _lock(PTHREAD_MUTEX_INITIALIZER) {}
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su_info::~su_info() {
pthread_mutex_destroy(&_lock);
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}
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mutex_guard su_info::lock() {
return mutex_guard(_lock);
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}
bool su_info::is_fresh() {
timespec ts;
clock_gettime(CLOCK_MONOTONIC, &ts);
long current = ts.tv_sec * 1000L + ts.tv_nsec / 1000000L;
return current - timestamp < 3000; /* 3 seconds */
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}
void su_info::refresh() {
timespec ts;
clock_gettime(CLOCK_MONOTONIC, &ts);
timestamp = ts.tv_sec * 1000L + ts.tv_nsec / 1000000L;
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}
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static void database_check(const shared_ptr<su_info> &info) {
int uid = info->uid;
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)
validate_manager(info->str[SU_MANAGER], uid / 100000, &info->mgr_st);
}
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static shared_ptr<su_info> get_su_info(unsigned uid) {
LOGD("su: request from uid=[%d]\n", uid);
shared_ptr<su_info> info;
{
mutex_guard lock(cache_lock);
if (!cached || cached->uid != uid || !cached->is_fresh())
cached = make_shared<su_info>(uid);
cached->refresh();
info = cached;
}
mutex_guard lock = info->lock();
if (info->access.policy == QUERY) {
// Not cached, get data from database
database_check(info);
// If it's root or the manager, allow it silently
if (info->uid == UID_ROOT || (info->uid % 100000) == (info->mgr_st.st_uid % 100000)) {
info->access = SILENT_SU_ACCESS;
return info;
}
// Check su access settings
switch (info->cfg[ROOT_ACCESS]) {
case ROOT_ACCESS_DISABLED:
LOGW("Root access is disabled!\n");
info->access = NO_SU_ACCESS;
break;
case ROOT_ACCESS_ADB_ONLY:
if (info->uid != UID_SHELL) {
LOGW("Root access limited to ADB only!\n");
info->access = NO_SU_ACCESS;
}
break;
case ROOT_ACCESS_APPS_ONLY:
if (info->uid == UID_SHELL) {
LOGW("Root access is disabled for ADB!\n");
info->access = NO_SU_ACCESS;
}
break;
case ROOT_ACCESS_APPS_AND_ADB:
default:
break;
}
if (info->access.policy != QUERY)
return info;
// If still not determined, check if manager exists
if (info->str[SU_MANAGER].empty()) {
info->access = NO_SU_ACCESS;
return info;
}
} else {
return info;
}
// If still not determined, ask manager
int fd = app_request(info);
if (fd < 0) {
info->access.policy = DENY;
} else {
int ret = read_int_be(fd);
info->access.policy = ret < 0 ? DENY : static_cast<policy_t>(ret);
close(fd);
}
return info;
}
// Set effective uid back to root, otherwise setres[ug]id will fail if uid isn't root
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static void set_identity(unsigned uid) {
if (seteuid(0)) {
PLOGE("seteuid (root)");
}
if (setresgid(uid, uid, uid)) {
PLOGE("setresgid (%u)", uid);
}
if (setresuid(uid, uid, uid)) {
PLOGE("setresuid (%u)", uid);
}
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}
void su_daemon_handler(int client, struct ucred *credential) {
LOGD("su: request from pid=[%d], client=[%d]\n", credential->pid, client);
su_context ctx = {
.info = get_su_info(credential->uid),
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.req = su_request(),
.pid = credential->pid
};
// Read su_request
xxread(client, &ctx.req, sizeof(su_req_base));
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read_string(client, ctx.req.shell);
read_string(client, ctx.req.command);
if (ctx.info->access.log)
app_log(ctx);
else if (ctx.info->access.notify)
app_notify(ctx);
// Fail fast
if (ctx.info->access.policy == DENY) {
LOGW("su: request rejected (%u)\n", ctx.info->uid);
ctx.info.reset();
write_int(client, DENY);
close(client);
return;
}
// Fork a child root process
//
// The child process will need to setsid, open a pseudo-terminal
// if needed, and eventually exec shell.
// The parent process will wait for the result and
// send the return code back to our client.
if (int child = xfork(); child) {
ctx.info.reset();
// Wait result
LOGD("su: waiting child pid=[%d]\n", child);
int status, code;
if (waitpid(child, &status, 0) > 0)
code = WEXITSTATUS(status);
else
code = -1;
LOGD("su: return code=[%d]\n", code);
write(client, &code, sizeof(code));
close(client);
return;
}
LOGD("su: fork handler\n");
// Abort upon any error occurred
log_cb.ex = exit;
// ack
write_int(client, 0);
// Become session leader
xsetsid();
// Get pts_slave
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string pts_slave = read_string(client);
// The FDs for each of the streams
int infd = recv_fd(client);
int outfd = recv_fd(client);
int errfd = recv_fd(client);
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if (!pts_slave.empty()) {
LOGD("su: pts_slave=[%s]\n", pts_slave.data());
// Check pts_slave file is owned by daemon_from_uid
struct stat st;
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xstat(pts_slave.data(), &st);
// If caller is not root, ensure the owner of pts_slave is the caller
if(st.st_uid != ctx.info->uid && ctx.info->uid != 0)
LOGE("su: Wrong permission of pts_slave\n");
// Opening the TTY has to occur after the
// fork() and setsid() so that it becomes
// our controlling TTY and not the daemon's
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int ptsfd = xopen(pts_slave.data(), O_RDWR);
if (infd < 0)
infd = ptsfd;
if (outfd < 0)
outfd = ptsfd;
if (errfd < 0)
errfd = ptsfd;
}
// Swap out stdin, stdout, stderr
xdup2(infd, STDIN_FILENO);
xdup2(outfd, STDOUT_FILENO);
xdup2(errfd, STDERR_FILENO);
// Unleash all streams from SELinux hell
setfilecon("/proc/self/fd/0", "u:object_r:" SEPOL_FILE_TYPE ":s0");
setfilecon("/proc/self/fd/1", "u:object_r:" SEPOL_FILE_TYPE ":s0");
setfilecon("/proc/self/fd/2", "u:object_r:" SEPOL_FILE_TYPE ":s0");
close(infd);
close(outfd);
close(errfd);
close(client);
// Handle namespaces
if (ctx.req.mount_master)
ctx.info->cfg[SU_MNT_NS] = NAMESPACE_MODE_GLOBAL;
switch (ctx.info->cfg[SU_MNT_NS]) {
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);
if (switch_mnt_ns(ctx.pid))
LOGD("su: setns failed, fallback to global\n");
break;
case NAMESPACE_MODE_ISOLATE:
LOGD("su: use new isolated namespace\n");
switch_mnt_ns(ctx.pid);
xunshare(CLONE_NEWNS);
xmount(nullptr, "/", nullptr, MS_PRIVATE | MS_REC, nullptr);
break;
}
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const char *argv[4] = { nullptr };
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argv[0] = ctx.req.login ? "-" : ctx.req.shell.data();
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if (!ctx.req.command.empty()) {
argv[1] = "-c";
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argv[2] = ctx.req.command.data();
}
// Setup environment
umask(022);
char path[32];
snprintf(path, sizeof(path), "/proc/%d/cwd", ctx.pid);
chdir(path);
snprintf(path, sizeof(path), "/proc/%d/environ", ctx.pid);
char buf[4096] = { 0 };
int fd = xopen(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);
setenv("USER", pw->pw_name, 1);
setenv("LOGNAME", pw->pw_name, 1);
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setenv("SHELL", ctx.req.shell.data(), 1);
}
}
// Unblock all signals
sigset_t block_set;
sigemptyset(&block_set);
sigprocmask(SIG_SETMASK, &block_set, nullptr);
set_identity(ctx.req.uid);
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execvp(ctx.req.shell.data(), (char **) argv);
fprintf(stderr, "Cannot execute %s: %s\n", ctx.req.shell.data(), strerror(errno));
PLOGE("exec");
exit(EXIT_FAILURE);
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}