From adf0d1bbfa4bc560c2106f14afa8258a11c48bf6 Mon Sep 17 00:00:00 2001
From: Elliott Hughes <enh@google.com>
Date: Wed, 22 Apr 2015 18:39:58 -0700
Subject: [PATCH] Make init re-exec itself for its SELinux domain transition.

Change-Id: I38adabe5789d671e3f7d21936071a758ec8cea8a
---
 init/init.cpp   | 61 +++++++++++++++++++++++++++++++++++++------------
 rootdir/init.rc |  7 ------
 2 files changed, 46 insertions(+), 22 deletions(-)

diff --git a/init/init.cpp b/init/init.cpp
index b1d65dbc0..ed20661f3 100644
--- a/init/init.cpp
+++ b/init/init.cpp
@@ -940,7 +940,13 @@ static int audit_callback(void *data, security_class_t /*cls*/, char *buf, size_
     return 0;
 }
 
-static void selinux_initialize() {
+static void security_failure() {
+    ERROR("Security failure; rebooting into recovery mode...\n");
+    android_reboot(ANDROID_RB_RESTART2, 0, "recovery");
+    while (true) { pause(); }  // never reached
+}
+
+static void selinux_initialize(bool in_kernel_domain) {
     Timer t;
 
     selinux_callback cb;
@@ -953,19 +959,27 @@ static void selinux_initialize() {
         return;
     }
 
-    INFO("Loading SELinux policy...\n");
-    if (selinux_android_load_policy() < 0) {
-        ERROR("SELinux: Failed to load policy; rebooting into recovery mode\n");
-        android_reboot(ANDROID_RB_RESTART2, 0, "recovery");
-        while (1) { pause(); }  // never reached
+    if (in_kernel_domain) {
+        if (write_file("/sys/fs/selinux/checkreqprot", "0") == -1) {
+            ERROR("couldn't write to /sys/fs/selinux/checkreqprot: %s\n",
+                  strerror(errno));
+            security_failure();
+        }
+
+        INFO("Loading SELinux policy...\n");
+        if (selinux_android_load_policy() < 0) {
+            ERROR("failed to load policy: %s\n", strerror(errno));
+            security_failure();
+        }
+
+        bool is_enforcing = selinux_is_enforcing();
+        security_setenforce(is_enforcing);
+
+        NOTICE("(Initializing SELinux %s took %.2fs.)\n",
+               is_enforcing ? "enforcing" : "non-enforcing", t.duration());
+    } else {
+        selinux_init_all_handles();
     }
-
-    selinux_init_all_handles();
-    bool is_enforcing = selinux_is_enforcing();
-    INFO("SELinux: security_setenforce(%d)\n", is_enforcing);
-    security_setenforce(is_enforcing);
-
-    NOTICE("(Initializing SELinux took %.2fs.)\n", t.duration());
 }
 
 int main(int argc, char** argv) {
@@ -1006,7 +1020,8 @@ int main(int argc, char** argv) {
     klog_init();
     klog_set_level(KLOG_NOTICE_LEVEL);
 
-    NOTICE("init started!\n");
+    bool is_first_stage = (argc == 1);
+    NOTICE("init%s started!\n", is_first_stage ? "" : " second stage");
 
     property_init();
 
@@ -1019,7 +1034,23 @@ int main(int argc, char** argv) {
     // used by init as well as the current required properties.
     export_kernel_boot_props();
 
-    selinux_initialize();
+    // Set up SELinux, including loading the SELinux policy if we're in the kernel domain.
+    selinux_initialize(is_first_stage);
+
+    // If we're in the kernel domain, re-exec init to transition to the init domain now
+    // that the SELinux policy has been loaded.
+    if (is_first_stage) {
+        if (restorecon("/init") == -1) {
+            ERROR("restorecon failed: %s\n", strerror(errno));
+            security_failure();
+        }
+        char* path = argv[0];
+        char* args[] = { path, const_cast<char*>("--second-stage"), nullptr };
+        if (execv(path, args) == -1) {
+            ERROR("execv(\"%s\") failed: %s\n", path, strerror(errno));
+            security_failure();
+        }
+    }
 
     // These directories were necessarily created before initial policy load
     // and therefore need their security context restored to the proper value.
diff --git a/rootdir/init.rc b/rootdir/init.rc
index a5ea60aaa..4d9c4f3f3 100644
--- a/rootdir/init.rc
+++ b/rootdir/init.rc
@@ -14,13 +14,6 @@ on early-init
     # Set init and its forked children's oom_adj.
     write /proc/1/oom_score_adj -1000
 
-    # Apply strict SELinux checking of PROT_EXEC on mmap/mprotect calls.
-    write /sys/fs/selinux/checkreqprot 0
-
-    # Set the security context for the init process.
-    # This should occur before anything else (e.g. ueventd) is started.
-    setcon u:r:init:s0
-
     # Set the security context of /adb_keys if present.
     restorecon /adb_keys