From 4327682120ec909523a586ee8324bfa74c82e2c7 Mon Sep 17 00:00:00 2001
From: LoveSy <shana@zju.edu.cn>
Date: Thu, 18 May 2023 02:08:25 +0800
Subject: [PATCH] Add mnt ns attach support for `su`

---
 native/src/su/su.cpp        | 19 +++++++++++++++++--
 native/src/su/su.hpp        |  2 +-
 native/src/su/su_daemon.cpp | 12 ++++++++----
 3 files changed, 26 insertions(+), 7 deletions(-)

diff --git a/native/src/su/su.cpp b/native/src/su/su.cpp
index 5ca0decc6..9cfd9cdce 100644
--- a/native/src/su/su.cpp
+++ b/native/src/su/su.cpp
@@ -31,6 +31,7 @@ int quit_signals[] = { SIGALRM, SIGABRT, SIGHUP, SIGPIPE, SIGQUIT, SIGTERM, SIGI
     "Options:\n"
     "  -c, --command COMMAND         pass COMMAND to the invoked shell\n"
     "  -z, --context CONTEXT         change SELinux context\n"
+    "  -t, --target PID              PID to take mount namespace from\n"
     "  -h, --help                    display this help message and exit\n"
     "  -, -l, --login                pretend the shell to be a login shell\n"
     "  -m, -p,\n"
@@ -86,6 +87,7 @@ int su_client_main(int argc, char *argv[]) {
             { "version",                no_argument,        nullptr, 'v' },
             { "context",                required_argument,  nullptr, 'z' },
             { "mount-master",           no_argument,        nullptr, 'M' },
+            { "target",                 required_argument,  nullptr, 't' },
             { nullptr, 0, nullptr, 0 },
     };
 
@@ -99,7 +101,7 @@ int su_client_main(int argc, char *argv[]) {
             strcpy(argv[i], "-M");
     }
 
-    while ((c = getopt_long(argc, argv, "c:hlmps:Vvuz:M", long_opts, nullptr)) != -1) {
+    while ((c = getopt_long(argc, argv, "c:hlmps:Vvuz:Mt:", long_opts, nullptr)) != -1) {
         switch (c) {
             case 'c':
                 for (int i = optind - 1; i < argc; ++i) {
@@ -131,7 +133,20 @@ int su_client_main(int argc, char *argv[]) {
                 su_req.context = optarg;
                 break;
             case 'M':
-                su_req.mount_master = true;
+            case 't':
+                if (su_req.target != -1) {
+                    fprintf(stderr, "Can't use -M and -t at the same time\n");
+                    usage(EXIT_FAILURE);
+                }
+                if (optarg == nullptr) {
+                    su_req.target = 0;
+                } else {
+                    su_req.target = parse_int(optarg);
+                    if (*optarg == '-' || su_req.target == -1) {
+                        fprintf(stderr, "Invalid PID: %s\n", optarg);
+                        usage(EXIT_FAILURE);
+                    }
+                }
                 break;
             default:
                 /* Bionic getopt_long doesn't terminate its error output by newline */
diff --git a/native/src/su/su.hpp b/native/src/su/su.hpp
index 5da86e5e5..2c9b14719 100644
--- a/native/src/su/su.hpp
+++ b/native/src/su/su.hpp
@@ -45,7 +45,7 @@ struct su_req_base {
     uid_t uid = AID_ROOT;
     bool login = false;
     bool keepenv = false;
-    bool mount_master = false;
+    pid_t target = -1;
 } __attribute__((packed));
 
 struct su_request : public su_req_base {
diff --git a/native/src/su/su_daemon.cpp b/native/src/su/su_daemon.cpp
index 7d29ab93b..1ceb6b556 100644
--- a/native/src/su/su_daemon.cpp
+++ b/native/src/su/su_daemon.cpp
@@ -395,20 +395,24 @@ void su_daemon_handler(int client, const sock_cred *cred) {
     close(client);
 
     // Handle namespaces
-    if (ctx.req.mount_master)
+    if (ctx.req.target == -1)
+        ctx.req.target = ctx.pid;
+    else if (ctx.req.target == 0)
         ctx.info->cfg[SU_MNT_NS] = NAMESPACE_MODE_GLOBAL;
+    else if (ctx.info->cfg[SU_MNT_NS] == NAMESPACE_MODE_GLOBAL)
+        ctx.info->cfg[SU_MNT_NS] = NAMESPACE_MODE_REQUESTER;
     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: use namespace of pid=[%d]\n", ctx.req.target);
+            if (switch_mnt_ns(ctx.req.target))
                 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);
+            switch_mnt_ns(ctx.req.target);
             xunshare(CLONE_NEWNS);
             xmount(nullptr, "/", nullptr, MS_PRIVATE | MS_REC, nullptr);
             break;