Run restorecon after init creates a symlink or writes to a file.

Init currently sets the SELinux context on a mkdir but not on
other operations.  This patch modifies it to do so when creating
symlinks, writing to a file, or copying a file.

Test: Built, flashed, and booted.  Added fake init entries and
verified that they received the proper SELinux context.

Change-Id: I836b570fef81d74f3b6c8e7ce0274e94ca7b12d3
diff --git a/init/util.cpp b/init/util.cpp
index a19a6f3..d80cb1e 100644
--- a/init/util.cpp
+++ b/init/util.cpp
@@ -178,9 +178,26 @@
     return content;
 }
 
+static int OpenFile(const std::string& path, int flags, mode_t mode) {
+    std::string secontext;
+    if (SelabelLookupFileContext(path, mode, &secontext) && !secontext.empty()) {
+        setfscreatecon(secontext.c_str());
+    }
+
+    int rc = open(path.c_str(), flags, mode);
+
+    if (!secontext.empty()) {
+        int save_errno = errno;
+        setfscreatecon(nullptr);
+        errno = save_errno;
+    }
+
+    return rc;
+}
+
 Result<Success> WriteFile(const std::string& path, const std::string& content) {
     android::base::unique_fd fd(TEMP_FAILURE_RETRY(
-        open(path.c_str(), O_WRONLY | O_CREAT | O_NOFOLLOW | O_TRUNC | O_CLOEXEC, 0600)));
+        OpenFile(path, O_WRONLY | O_CREAT | O_NOFOLLOW | O_TRUNC | O_CLOEXEC, 0600)));
     if (fd == -1) {
         return ErrnoError() << "open() failed";
     }