NatController.cpp revision b5ff9b277f256df84caf3d798ccc83b4740a1d31 
1/*
2 * Copyright (C) 2008 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#include <stdlib.h>
18#include <errno.h>
19#include <sys/socket.h>
20#include <sys/stat.h>
21#include <fcntl.h>
22#include <netinet/in.h>
23#include <arpa/inet.h>
24
25#define LOG_TAG "NatController"
26#include <cutils/log.h>
27
28#include "NatController.h"
29
30extern "C" int logwrap(int argc, const char **argv, int background);
31
32static char IPTABLES_PATH[] = "/system/bin/iptables";
33
34NatController::NatController() {
35    natCount = 0;
36}
37
38NatController::~NatController() {
39}
40
41int NatController::runIptablesCmd(const char *cmd) {
42    char buffer[255];
43
44    strncpy(buffer, cmd, sizeof(buffer)-1);
45
46    const char *args[16];
47    char *next = buffer;
48    char *tmp;
49
50    args[0] = IPTABLES_PATH;
51    args[1] = "--verbose";
52    int i = 2;
53
54    while ((tmp = strsep(&next, " "))) {
55        args[i++] = tmp;
56        if (i == 16) {
57            LOGE("iptables argument overflow");
58            errno = E2BIG;
59            return -1;
60        }
61    }
62    args[i] = NULL;
63
64    return logwrap(i, args, 0);
65}
66
67int NatController::setDefaults() {
68
69    if (runIptablesCmd("-P INPUT ACCEPT"))
70        return -1;
71    if (runIptablesCmd("-F INPUT"))
72        return -1;
73    if (runIptablesCmd("-P OUTPUT ACCEPT"))
74        return -1;
75    if (runIptablesCmd("-F OUTPUT"))
76        return -1;
77    if (runIptablesCmd("-P FORWARD DROP"))
78        return -1;
79    if (runIptablesCmd("-F FORWARD"))
80        return -1;
81    if (runIptablesCmd("-t nat -F"))
82        return -1;
83    return 0;
84}
85
86bool NatController::interfaceExists(const char *iface) {
87    // XXX: Implement this
88    return true;
89}
90
91int NatController::doNatCommands(const char *intIface, const char *extIface, bool add) {
92    char cmd[255];
93
94    // handle decrement to 0 case (do reset to defaults) and erroneous dec below 0
95    if (add == false) {
96        if (natCount <= 1) {
97            int ret = setDefaults();
98            if (ret == 0) {
99                natCount=0;
100            }
101            return ret;
102        }
103    }
104
105    if (!interfaceExists(intIface) || !interfaceExists (extIface)) {
106        LOGE("Invalid interface specified");
107        errno = ENODEV;
108        return -1;
109    }
110
111    snprintf(cmd, sizeof(cmd),
112             "-%s FORWARD -i %s -o %s -m state --state ESTABLISHED,RELATED -j ACCEPT",
113             (add ? "A" : "D"),
114             extIface, intIface);
115    if (runIptablesCmd(cmd)) {
116        return -1;
117    }
118
119    snprintf(cmd, sizeof(cmd), "-%s FORWARD -i %s -o %s -j ACCEPT", (add ? "A" : "D"),
120            intIface, extIface);
121    if (runIptablesCmd(cmd)) {
122        // unwind what's been done, but don't care about success - what more could we do?
123        snprintf(cmd, sizeof(cmd),
124                 "-%s FORWARD -i %s -o %s -m state --state ESTABLISHED,RELATED -j ACCEPT",
125                 (!add ? "A" : "D"),
126                 extIface, intIface);
127        return -1;
128    }
129
130    // add this if we are the first added nat
131    if (add && natCount == 0) {
132        snprintf(cmd, sizeof(cmd), "-t nat -A POSTROUTING -o %s -j MASQUERADE", extIface);
133        if (runIptablesCmd(cmd)) {
134            // unwind what's been done, but don't care about success - what more could we do?
135            setDefaults();;
136            return -1;
137        }
138    }
139
140    if (add) {
141        natCount++;
142    } else {
143        natCount--;
144    }
145    return 0;
146}
147
148int NatController::enableNat(const char *intIface, const char *extIface) {
149    return doNatCommands(intIface, extIface, true);
150}
151
152int NatController::disableNat(const char *intIface, const char *extIface) {
153    return doNatCommands(intIface, extIface, false);
154}
155