Support settings gids of su

native/src/include/socket.hpp

@@ -22,3 +22,17 @@ void write_int_be(int fd, int val);
 std::string read_string(int fd);
 bool read_string(int fd, std::string &str);
 void write_string(int fd, std::string_view str);
+
+template<typename T> requires(std::is_trivially_copyable_v<T>)
+void write_vector(int fd, const std::vector<T> &vec) {
+    write_int(fd, static_cast<int>(vec.size()));
+    xwrite(fd, vec.data(), vec.size() * sizeof(T));
+}
+
+template<typename T> requires(std::is_trivially_copyable_v<T>)
+bool read_vector(int fd, std::vector<T> &vec) {
+    int size = read_int(fd);
+    if (size == -1) return false;
+    vec.resize(size);
+    return xread(fd, vec.data(), size * sizeof(T)) == size * sizeof(T);
+}

native/src/su/connect.cpp

@@ -166,7 +166,7 @@ void app_log(const su_context &ctx) {
         vector<Extra> extras;
         extras.reserve(6);
         extras.emplace_back("from.uid", ctx.info->uid);
-        extras.emplace_back("to.uid", ctx.req.uid);
+        extras.emplace_back("to.uid", static_cast<int>(ctx.req.uid));
         extras.emplace_back("pid", ctx.pid);
         extras.emplace_back("policy", ctx.info->access.policy);
         extras.emplace_back("command", get_cmd(ctx.req));

native/src/su/su.cpp

@@ -22,12 +22,12 @@
 
 int quit_signals[] = { SIGALRM, SIGABRT, SIGHUP, SIGPIPE, SIGQUIT, SIGTERM, SIGINT, 0 };
 
-static void usage(int status) {
+[[noreturn]] static void usage(int status) {
     FILE *stream = (status == EXIT_SUCCESS) ? stdout : stderr;
 
     fprintf(stream,
     "MagiskSU\n\n"
-    "Usage: su [options] [-] [user [argument...]]\n\n"
+    "Usage: su [options] [-] [user[:group,...] [argument...]]\n\n"
     "Options:\n"
     "  -c, --command COMMAND         pass COMMAND to the invoked shell\n"
     "  -h, --help                    display this help message and exit\n"
@@ -110,7 +110,6 @@ int su_client_main(int argc, char *argv[]) {
                 break;
             case 'h':
                 usage(EXIT_SUCCESS);
-                break;
             case 'l':
                 su_req.login = true;
                 break;
@@ -146,12 +145,19 @@ int su_client_main(int argc, char *argv[]) {
     }
     /* username or uid */
     if (optind < argc) {
+        std::string_view uidgid = argv[optind];
+        auto sep = split_view(uidgid, ":");
+        if (sep.size() > 2) usage(EXIT_FAILURE);
+        auto user = std::string(sep[0]);
         struct passwd *pw;
-        pw = getpwnam(argv[optind]);
-        if (pw)
-            su_req.uid = pw->pw_uid;
-        else
-            su_req.uid = parse_int(argv[optind]);
+        pw = getpwnam(user.data());
+        su_req.uid = pw ? pw->pw_uid : parse_int(user);
+        if (sep.size() == 2) {
+            for (auto group : split_view(sep[1], ",")) {
+                pw = getpwnam(std::string(group).data());
+                su_req.gids.push_back(pw ? pw->pw_gid : parse_int(group));
+            }
+        }
         optind++;
     }
 
@@ -164,6 +170,7 @@ int su_client_main(int argc, char *argv[]) {
     xwrite(fd, &su_req, sizeof(su_req_base));
     write_string(fd, su_req.shell);
     write_string(fd, su_req.command);
+    write_vector(fd, su_req.gids);
 
     // Wait for ack from daemon
     if (read_int(fd)) {

native/src/su/su.hpp

@@ -42,7 +42,7 @@ private:
 };
 
 struct su_req_base {
-    int uid = AID_ROOT;
+    uid_t uid = AID_ROOT;
     bool login = false;
     bool keepenv = false;
     bool mount_master = false;
@@ -51,6 +51,7 @@ struct su_req_base {
 struct su_request : public su_req_base {
     std::string shell = DEFAULT_SHELL;
     std::string command;
+    std::vector<gid_t> gids;
 };
 
 struct su_context {

native/src/su/su_daemon.cpp

@@ -230,11 +230,20 @@ static shared_ptr<su_info> get_su_info(unsigned uid) {
 }
 
 // Set effective uid back to root, otherwise setres[ug]id will fail if uid isn't root
-static void set_identity(unsigned uid) {
+static void set_identity(uid_t uid, const std::vector<uid_t> &groups) {
     if (seteuid(0)) {
         PLOGE("seteuid (root)");
     }
-    if (setresgid(uid, uid, uid)) {
+    gid_t gid;
+    if (groups.size() > 0) {
+        if (setgroups(groups.size(), groups.data())) {
+            PLOGE("setgroups");
+        }
+        gid = groups[0];
+    } else {
+        gid = uid;
+    }
+    if (setresgid(gid, gid, gid)) {
         PLOGE("setresgid (%u)", uid);
     }
     if (setresuid(uid, uid, uid)) {
@@ -254,7 +263,8 @@ void su_daemon_handler(int client, const sock_cred *cred) {
     // Read su_request
     if (xxread(client, &ctx.req, sizeof(su_req_base)) < 0
         || !read_string(client, ctx.req.shell)
-        || !read_string(client, ctx.req.command)) {
+        || !read_string(client, ctx.req.command)
+        || !read_vector(client, ctx.req.gids)) {
         LOGW("su: remote process probably died, abort\n");
         ctx.info.reset();
         write_int(client, DENY);
@@ -443,7 +453,7 @@ void su_daemon_handler(int client, const sock_cred *cred) {
     sigset_t block_set;
     sigemptyset(&block_set);
     sigprocmask(SIG_SETMASK, &block_set, nullptr);
-    set_identity(ctx.req.uid);
+    set_identity(ctx.req.uid, ctx.req.gids);
     execvp(ctx.req.shell.data(), (char **) argv);
     fprintf(stderr, "Cannot execute %s: %s\n", ctx.req.shell.data(), strerror(errno));
     PLOGE("exec");