J9 Allow attachment as root (#1631)

* Allow attachment as root

* Add javadoc for getUserId

Author: FelixMarxIBM

byte-buddy-agent/src/main/java/net/bytebuddy/agent/VirtualMachine.java

@@ -1660,49 +1660,23 @@ protected ForOpenJ9(Socket socket) {
          * @throws IOException If an IO exception occurs during establishing the connection.
          */
         public static VirtualMachine attach(String processId) throws IOException {
-            return attach(processId, false);
-        }
-
-        /**
-         * Attaches to the supplied process id using the default JNA implementation.
-         *
-         * @param processId  The process id.
-         * @param ignoreUser {@code true} if VM processes that are owned by different users should be considered.
-         * @return A suitable virtual machine implementation.
-         * @throws IOException If an IO exception occurs during establishing the connection.
-         */
-        public static VirtualMachine attach(String processId, boolean ignoreUser) throws IOException {
             return attach(processId, 5000, Platform.isWindows()
                     ? new Dispatcher.ForJnaWindowsEnvironment()
                     : new Dispatcher.ForJnaPosixEnvironment(15, 100, TimeUnit.MILLISECONDS));
         }
 
-        /**
-         * Attaches to the supplied process id. This method will not consider attaching to VMs owned by
-         * different users than the current user.
-         *
-         * @param processId  The process id.
-         * @param timeout    The timeout for establishing the socket connection.
-         * @param dispatcher The connector to use to communicate with the target VM.
-         * @return A suitable virtual machine implementation.
-         * @throws IOException If an IO exception occurs during establishing the connection.
-         */
-        public static VirtualMachine attach(String processId, int timeout, Dispatcher dispatcher) throws IOException {
-            return attach(processId, timeout, dispatcher, false);
-        }
-
         /**
          * Attaches to the supplied process id.
          *
          * @param processId  The process id.
          * @param timeout    The timeout for establishing the socket connection.
          * @param dispatcher The connector to use to communicate with the target VM.
-         * @param ignoreUser {@code true} if VM processes that are owned by different users should be considered.
          * @return A suitable virtual machine implementation.
          * @throws IOException If an IO exception occurs during establishing the connection.
          */
-        public static VirtualMachine attach(String processId, int timeout, Dispatcher dispatcher, boolean ignoreUser) throws IOException {
+        public static VirtualMachine attach(String processId, int timeout, Dispatcher dispatcher) throws IOException {
             File directory = new File(System.getProperty(IBM_TEMPORARY_FOLDER, dispatcher.getTemporaryFolder(processId)), ".com_ibm_tools_attach");
+            long userId = dispatcher.userId();
             RandomAccessFile attachLock = new RandomAccessFile(new File(directory, "_attachlock"), "rw");
             try {
                 FileLock attachLockLock = attachLock.getChannel().lock();
@@ -1716,10 +1690,9 @@ public static VirtualMachine attach(String processId, int timeout, Dispatcher di
                             if (vmFolder == null) {
                                 throw new IllegalStateException("No descriptor files found in " + directory);
                             }
-                            long userId = dispatcher.userId();
                             virtualMachines = new ArrayList<Properties>();
                             for (File aVmFolder : vmFolder) {
-                                if (aVmFolder.isDirectory() && (ignoreUser || dispatcher.getOwnerIdOf(aVmFolder) == userId)) {
+                                if (aVmFolder.isDirectory() && isFileOwnedByUid(dispatcher, aVmFolder, userId)) {
                                     File attachInfo = new File(aVmFolder, "attachInfo");
                                     if (attachInfo.isFile()) {
                                         Properties virtualMachine = new Properties();
@@ -1730,12 +1703,7 @@ public static VirtualMachine attach(String processId, int timeout, Dispatcher di
                                             inputStream.close();
                                         }
                                         int targetProcessId = Integer.parseInt(virtualMachine.getProperty("processId"));
-                                        long targetUserId;
-                                        try {
-                                            targetUserId = Long.parseLong(virtualMachine.getProperty("userUid"));
-                                        } catch (NumberFormatException ignored) {
-                                            targetUserId = 0L;
-                                        }
+                                        long targetUserId = getUserId(virtualMachine);
                                         if (userId != 0L && targetUserId == 0L) {
                                             targetUserId = dispatcher.getOwnerIdOf(attachInfo);
                                         }
@@ -1782,10 +1750,14 @@ public static VirtualMachine attach(String processId, int timeout, Dispatcher di
                             key = Long.toHexString(SECURE_RANDOM.nextLong());
                         }
                         File reply = new File(receiver, "replyInfo");
+                        long targetUserId = getUserId(target);
                         try {
                             if (reply.createNewFile()) {
                                 dispatcher.setPermissions(reply, 0600);
                             }
+                            if (0 == userId && 0 != targetUserId) {
+                                dispatcher.chownFileToTargetUid(reply, targetUserId);
+                            }
                             FileOutputStream outputStream = new FileOutputStream(reply);
                             try {
                                 outputStream.write(key.getBytes("UTF-8"));
@@ -1867,6 +1839,31 @@ public static VirtualMachine attach(String processId, int timeout, Dispatcher di
             }
         }
 
+        /**
+         * Returns the userUid present in the virtualMachine properties file
+         * @param virtualMachine Properties of the J9 attachInfo file
+         * @return the userUid if it can be parsed, <code>0L</code> otherwise.
+         */
+        private static long getUserId(Properties virtualMachine) {
+            long targetUserId;
+            try {
+                targetUserId = Long.parseLong(virtualMachine.getProperty("userUid"));
+            } catch (NumberFormatException ignored) {
+                targetUserId = 0L;
+            }
+            return targetUserId;
+        }
+
+        /**
+         * Check if the file is owned by the UID.  Note that UID 0 "owns" all files.
+         * @param aVmFolder File or directory
+         * @param userId user UID.
+         * @return true if the uid owns the file or uid == 0.
+         */
+        private static boolean isFileOwnedByUid(Dispatcher dispatcher, File aVmFolder, long userId) {
+            return 0 == userId || dispatcher.getOwnerIdOf(aVmFolder) == userId;
+        }
+
         /**
          * {@inheritDoc}
          */
@@ -2077,6 +2074,13 @@ public interface Dispatcher {
              */
             void decrementSemaphore(File directory, String name, boolean global, int count);
 
+            /**
+             * change the ownership of a file.  Can be called only if this process is owned by root.
+             * @param path path to the file
+             * @param targetUserId effective userid
+             */
+            void chownFileToTargetUid(File path, long targetUserId);
+
             /**
              * A connector implementation for a POSIX environment using JNA.
              */
@@ -2214,6 +2218,14 @@ public void decrementSemaphore(File directory, String name, boolean global, int
                     notifySemaphore(directory, name, count, (short) -1, (short) (PosixLibrary.SEM_UNDO | PosixLibrary.IPC_NOWAIT), true);
                 }
 
+                /**
+                 * {@inheritDoc}
+                 */
+                @Override
+                public void chownFileToTargetUid(File file, long targetUserId) {
+                    library.chown(file.getAbsolutePath(), targetUserId);
+                }
+
                 /**
                  * Notifies a POSIX semaphore.
                  *
@@ -2319,6 +2331,16 @@ protected interface PosixLibrary extends Library {
                      */
                     int chmod(String path, int mode) throws LastErrorException;
 
+                    /**
+                     * Runs the {@code chown} command.
+                     *
+                     * @param path The file path.
+                     * @param uid The userid to set.
+                     * @return The return code.
+                     * @throws LastErrorException If an error occurred.
+                     */
+                    int chown(String path, long uid) throws LastErrorException;
+
                     /**
                      * Runs the {@code ftok} command.
                      *
@@ -2502,6 +2524,14 @@ public void decrementSemaphore(File directory, String name, boolean global, int
                     }
                 }
 
+                /**
+                 * {@inheritDoc}
+                 */
+                @Override
+                public void chownFileToTargetUid(File path, long targetUserId) {
+                    /* do nothing */
+                }
+
                 /**
                  * Opens a semaphore for signaling another process that an attachment is performed.
                  *