DHCP: Add a native method for making a DHCP socket.

Bug: 19704592
Change-Id: Iadd60d39c93aaabd2917e76791101a7d313b34be

core/java/android/net/NetworkUtils.java

@@ -16,9 +16,11 @@
 
 package android.net;
 
+import java.io.FileDescriptor;
 import java.net.InetAddress;
 import java.net.Inet4Address;
 import java.net.Inet6Address;
+import java.net.SocketException;
 import java.net.UnknownHostException;
 import java.util.Collection;
 import java.util.Locale;
@@ -138,6 +140,11 @@ public class NetworkUtils {
      */
     public native static String getDhcpError();
 
+    /**
+     * Attaches a socket filter that accepts DHCP packets to the given socket.
+     */
+    public native static void attachDhcpFilter(FileDescriptor fd) throws SocketException;
+
     /**
      * Binds the current process to the network designated by {@code netId}.  All sockets created
      * in the future (and not explicitly bound via a bound {@link SocketFactory} (see

core/jni/android_net_NetUtils.cpp

@@ -23,6 +23,14 @@
 #include <android_runtime/AndroidRuntime.h>
 #include <utils/Log.h>
 #include <arpa/inet.h>
+#include <net/if.h>
+#include <linux/filter.h>
+#include <linux/if.h>
+#include <linux/if_ether.h>
+#include <linux/if_packet.h>
+#include <net/if_ether.h>
+#include <netinet/ip.h>
+#include <netinet/udp.h>
 #include <cutils/properties.h>
 
 #include "core_jni_helpers.h"
@@ -54,6 +62,8 @@ char *dhcp_get_errmsg();
 
 namespace android {
 
+static const uint16_t kDhcpClientPort = 68;
+
 /*
  * The following remembers the jfieldID's of the fields
  * of the DhcpInfo Java object, so that we don't have
@@ -216,6 +226,44 @@ static jstring android_net_utils_getDhcpError(JNIEnv* env, jobject clazz)
     return env->NewStringUTF(::dhcp_get_errmsg());
 }
 
+static void android_net_utils_attachDhcpFilter(JNIEnv *env, jobject clazz, jobject javaFd)
+{
+    int fd = jniGetFDFromFileDescriptor(env, javaFd);
+    uint32_t ip_offset = sizeof(ether_header);
+    uint32_t proto_offset = ip_offset + offsetof(iphdr, protocol);
+    uint32_t flags_offset = ip_offset +  offsetof(iphdr, frag_off);
+    uint32_t dport_indirect_offset = ip_offset + offsetof(udphdr, dest);
+    struct sock_filter filter_code[] = {
+        // Check the protocol is UDP.
+        BPF_STMT(BPF_LD  | BPF_B   | BPF_ABS,  proto_offset),
+        BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K,    IPPROTO_UDP, 0, 6),
+
+        // Check this is not a fragment.
+        BPF_STMT(BPF_LD  | BPF_H    | BPF_ABS, flags_offset),
+        BPF_JUMP(BPF_JMP | BPF_JSET | BPF_K,   0x1fff, 4, 0),
+
+        // Get the IP header length.
+        BPF_STMT(BPF_LDX | BPF_B    | BPF_MSH, ip_offset),
+
+        // Check the destination port.
+        BPF_STMT(BPF_LD  | BPF_H    | BPF_IND, dport_indirect_offset),
+        BPF_JUMP(BPF_JMP | BPF_JEQ  | BPF_K,   kDhcpClientPort, 0, 1),
+
+        // Accept or reject.
+        BPF_STMT(BPF_RET | BPF_K,              0xffff),
+        BPF_STMT(BPF_RET | BPF_K,              0)
+    };
+    struct sock_fprog filter = {
+        sizeof(filter_code) / sizeof(filter_code[0]),
+        filter_code,
+    };
+
+    if (setsockopt(fd, SOL_SOCKET, SO_ATTACH_FILTER, &filter, sizeof(filter)) != 0) {
+        jniThrowExceptionFmt(env, "java/net/SocketException",
+                "setsockopt(SO_ATTACH_FILTER): %s", strerror(errno));
+    }
+}
+
 static jboolean android_net_utils_bindProcessToNetwork(JNIEnv *env, jobject thiz, jint netId)
 {
     return (jboolean) !setNetworkForProcess(netId);
@@ -243,6 +291,7 @@ static jboolean android_net_utils_protectFromVpn(JNIEnv *env, jobject thiz, jint
     return (jboolean) !protectFromVpn(socket);
 }
 
+
 // ----------------------------------------------------------------------------
 
 /*
@@ -262,6 +311,7 @@ static JNINativeMethod gNetworkUtilMethods[] = {
     { "bindProcessToNetworkForHostResolution", "(I)Z", (void*) android_net_utils_bindProcessToNetworkForHostResolution },
     { "bindSocketToNetwork", "(II)I", (void*) android_net_utils_bindSocketToNetwork },
     { "protectFromVpn", "(I)Z", (void*)android_net_utils_protectFromVpn },
+    { "attachDhcpFilter", "(Ljava/io/FileDescriptor;)V", (void*) android_net_utils_attachDhcpFilter },
 };
 
 int register_android_net_NetworkUtils(JNIEnv* env)