Added support to fetch the UID, GID, and PID of the connected unix domain socket (EG: SO_PEERCREDS)

Motivation:

I had a need to know the user credentials of a connected unix domain socket.

Modifications:

Added a class to encapsulate user credentials (UID, GID, and the PID).
Augemented the Socket class to provide the JNI native interface to return this new class
Augemented the c code to call getSockOpts passing <a href=http://man7.org/linux/man-pages/man7/socket.7.html>SO_PEERCRED</a>
Then surfaced the ability to get user credentials in the EpollDomainSocketChannel

Result:

The EpollDomainSocketChannel now has a the following function signature:
public PeerCredentials peerCredentials() throws IOException allowing a caller to get the UID, GID, and PID of the linux process
connected to the unix domain socket.

transport-native-epoll/src/main/c/netty_unix_socket.c

@@ -13,6 +13,12 @@
  * License for the specific language governing permissions and limitations
  * under the License.
  */
+ /* 
+ * Since glibc 2.8, the _GNU_SOURCE feature test macro must be defined
+ * (before including any header files) in order to obtain the
+ * definition of this structure. See <a href=https://linux.die.net/man/7/unix>
+ */
+#define _GNU_SOURCE
 #include <fcntl.h>
 #include <errno.h>
 #include <unistd.h>
@@ -29,8 +35,10 @@
 #include "netty_unix_util.h"
 
 static jclass datagramSocketAddressClass = NULL;
+static jclass peerCredentialsClass = NULL;
 static jmethodID datagramSocketAddrMethodId = NULL;
 static jmethodID inetSocketAddrMethodId = NULL;
+static jmethodID peerCredentialsMethodId = NULL;
 static jclass inetSocketAddressClass = NULL;
 static jclass netUtilClass = NULL;
 static jmethodID netUtilClassIpv4PreferredMethodId = NULL;
@@ -647,6 +655,14 @@ static jint netty_unix_socket_isTcpQuickAck(JNIEnv* env, jclass clazz, jint fd)
     }
     return optval;
 }
+
+static jobject netty_channel_unix_socket_getPeerCredentials(JNIEnv *env, jclass clazz, jint fd) {
+     struct ucred credentials;
+     if(netty_unix_socket_getOption(env,fd, SOL_SOCKET, SO_PEERCRED, &credentials, sizeof (credentials))) {
+         return NULL;
+     }
+     return (*env)->NewObject(env, peerCredentialsClass, peerCredentialsMethodId, credentials.pid, credentials.uid, credentials.gid);
+}
 // JNI Registered Methods End
 
 // JNI Method Registration Table Begin
@@ -690,7 +706,7 @@ static const JNINativeMethod fixed_method_table[] = {
 static const jint fixed_method_table_size = sizeof(fixed_method_table) / sizeof(fixed_method_table[0]);
 
 static jint dynamicMethodsTableSize() {
-    return fixed_method_table_size + 2;
+    return fixed_method_table_size + 3;
 }
 
 static JNINativeMethod* createDynamicMethodsTable(const char* packagePrefix) {
@@ -708,6 +724,12 @@ static JNINativeMethod* createDynamicMethodsTable(const char* packagePrefix) {
     dynamicMethod->signature = netty_unix_util_prepend("(IJII)L", dynamicTypeName);
     dynamicMethod->fnPtr = (void *) netty_unix_socket_recvFromAddress;
     free(dynamicTypeName);
+    ++dynamicMethod;
+    dynamicTypeName = netty_unix_util_prepend(packagePrefix, "io/netty/channel/unix/PeerCredentials;");
+    dynamicMethod->name = "getPeerCredentials";
+    dynamicMethod->signature = netty_unix_util_prepend("(I)L", dynamicTypeName);
+    dynamicMethod->fnPtr = (void *) netty_channel_unix_socket_getPeerCredentials;
+    free(dynamicTypeName);
     return dynamicMethods;
 }
 
@@ -789,6 +811,26 @@ jint netty_unix_socket_JNI_OnLoad(JNIEnv* env, const char* packagePrefix) {
         return JNI_ERR;
     }
     
+    nettyClassName = netty_unix_util_prepend(packagePrefix, "io/netty/channel/unix/PeerCredentials");
+    jclass localPeerCredsClass = (*env)->FindClass(env, nettyClassName);
+    free(nettyClassName);
+    nettyClassName = NULL;
+    if (localPeerCredsClass == NULL) {
+        // pending exception...
+        return JNI_ERR;
+    }
+    peerCredentialsClass = (jclass) (*env)->NewGlobalRef(env, localPeerCredsClass);
+    if (peerCredentialsClass == NULL) {
+        // out-of-memory!
+        netty_unix_errors_throwOutOfMemoryError(env);
+        return JNI_ERR;
+    }
+    peerCredentialsMethodId = (*env)->GetMethodID(env, peerCredentialsClass, "<init>", "(III)V");
+    if (peerCredentialsMethodId == NULL) {
+        netty_unix_errors_throwRuntimeException(env, "failed to get method ID: PeerCredentials.<init>(int, int, int)");
+        return JNI_ERR;
+    }
+
     void* mem = malloc(1);
     if (mem == NULL) {
         netty_unix_errors_throwOutOfMemoryError(env);
@@ -826,4 +868,8 @@ void netty_unix_socket_JNI_OnUnLoad(JNIEnv* env) {
         (*env)->DeleteGlobalRef(env, netUtilClass);
         netUtilClass = NULL;
     }
+    if (peerCredentialsClass != NULL) {
+        (*env)->DeleteGlobalRef(env, peerCredentialsClass);
+        peerCredentialsClass = NULL;
+    }
 }

transport-native-epoll/src/main/java/io/netty/channel/epoll/EpollDomainSocketChannel.java

@@ -22,11 +22,13 @@ import io.netty.channel.ChannelPipeline;
 import io.netty.channel.unix.DomainSocketAddress;
 import io.netty.channel.unix.DomainSocketChannel;
 import io.netty.channel.unix.FileDescriptor;
+import io.netty.channel.unix.PeerCredentials;
 import io.netty.channel.unix.Socket;
 
 import java.net.SocketAddress;
 
 import static io.netty.channel.unix.Socket.newSocketDomain;
+import java.io.IOException;
 
 public final class EpollDomainSocketChannel extends AbstractEpollStreamChannel implements DomainSocketChannel {
     private final EpollDomainSocketChannelConfig config = new EpollDomainSocketChannelConfig(this);
@@ -132,6 +134,14 @@ public final class EpollDomainSocketChannel extends AbstractEpollStreamChannel i
         return super.filterOutboundMessage(msg);
     }
 
+    /**
+     * Returns the unix credentials (uid, gid, pid) of the peer
+     * <a href=http://man7.org/linux/man-pages/man7/socket.7.html>SO_PEERCRED</a>
+     */
+    public PeerCredentials peerCredentials() throws IOException {
+        return fd().getPeerCredentials();
+    }
+
     private final class EpollDomainUnsafe extends EpollStreamUnsafe {
         @Override
         void epollInReady() {

transport-native-epoll/src/main/java/io/netty/channel/unix/PeerCredentials.java

@@ -0,0 +1,58 @@
+/*
+ * Copyright 2016 The Netty Project
+ *
+ * The Netty Project licenses this file to you under the Apache License,
+ * version 2.0 (the "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at:
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ */
+
+package io.netty.channel.unix;
+
+/**
+ * User credentials discovered for the peer unix domain socket.
+ *
+ * The PID, UID and GID of the user connected on the other side of the unix domain socket
+ * For details see:
+ * <a href=http://man7.org/linux/man-pages/man7/socket.7.html>SO_PEERCRED</a>
+ */
+public final class PeerCredentials {
+    private final int pid;
+    private final int uid;
+    private final int gid;
+
+    // These values are set by JNI via Socket.peerCredentials()
+    PeerCredentials(int p, int u, int g) {
+        pid = p;
+        uid = u;
+        gid = g;
+    }
+
+    public int pid() {
+        return pid;
+    }
+
+    public int uid() {
+        return uid;
+    }
+
+    public int gid() {
+        return gid;
+    }
+
+    @Override
+    public String toString() {
+        return "UserCredentials["
+        + "pid=" + pid
+        + "; uid=" + uid
+        + "; gid=" + gid
+        + "]";
+    }
+}

transport-native-epoll/src/main/java/io/netty/channel/unix/Socket.java

@@ -319,6 +319,10 @@ public final class Socket extends FileDescriptor {
         return getSoError(fd);
     }
 
+    public PeerCredentials getPeerCredentials() throws IOException {
+        return getPeerCredentials(fd);
+    }
+
     public void setKeepAlive(boolean keepAlive) throws IOException {
         setKeepAlive(fd, keepAlive ? 1 : 0);
     }
@@ -419,6 +423,7 @@ public final class Socket extends FileDescriptor {
     private static native int getSoError(int fd) throws IOException;
     private static native int getTcpDeferAccept(int fd) throws IOException;
     private static native int isTcpQuickAck(int fd) throws IOException;
+    private static native PeerCredentials getPeerCredentials(int fd) throws IOException;
 
     private static native void setKeepAlive(int fd, int keepAlive) throws IOException;
     private static native void setReceiveBufferSize(int fd, int receiveBufferSize) throws IOException;

transport-native-epoll/src/test/java/io/netty/channel/unix/SocketTest.java

@@ -16,6 +16,7 @@
 package io.netty.channel.unix;
 
 import io.netty.channel.epoll.Epoll;
+import java.io.File;
 import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
@@ -96,4 +97,30 @@ public class SocketTest {
         socket.close();
         socket.close();
     }
+
+    @Test
+    public void testPeerCreds() throws IOException {
+        Socket s1 = Socket.newSocketDomain();
+        Socket s2 = Socket.newSocketDomain();
+        File domainSocketFile = null;
+
+        try {
+            domainSocketFile = File.createTempFile("netty-test", "sckt");
+            DomainSocketAddress dsa = new DomainSocketAddress(domainSocketFile);
+            s1.bind(dsa);
+            s1.listen(1);
+
+            assertTrue(s2.connect(dsa));
+            byte [] addr = new byte[64];
+            s1.accept(addr);
+            PeerCredentials pc = s1.getPeerCredentials();
+            assertNotEquals(pc.uid(), -1);
+        } finally {
+            s1.close();
+            s2.close();
+            if (domainSocketFile != null) {
+                domainSocketFile.delete();
+            }
+        }
+    }
 }