NatController.cpp revision ff2c0d8c13457e43f0d4bf06d3177271aac104c1 
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#include <string.h>
25
26#define LOG_TAG "NatController"
27#include <cutils/log.h>
28
29#include "NatController.h"
30
31extern "C" int logwrap(int argc, const char **argv, int background);
32
33static char IPTABLES_PATH[] = "/system/bin/iptables";
34
35NatController::NatController() {
36    natCount = 0;
37}
38
39NatController::~NatController() {
40}
41
42int NatController::runIptablesCmd(const char *cmd) {
43    char buffer[255];
44
45    strncpy(buffer, cmd, sizeof(buffer)-1);
46
47    const char *args[16];
48    char *next = buffer;
49    char *tmp;
50
51    args[0] = IPTABLES_PATH;
52    args[1] = "--verbose";
53    int i = 2;
54
55    while ((tmp = strsep(&next, " "))) {
56        args[i++] = tmp;
57        if (i == 16) {
58            LOGE("iptables argument overflow");
59            errno = E2BIG;
60            return -1;
61        }
62    }
63    args[i] = NULL;
64
65    return logwrap(i, args, 0);
66}
67
68int NatController::setDefaults() {
69
70    if (runIptablesCmd("-P INPUT ACCEPT"))
71        return -1;
72    if (runIptablesCmd("-F INPUT"))
73        return -1;
74    if (runIptablesCmd("-P OUTPUT ACCEPT"))
75        return -1;
76    if (runIptablesCmd("-F OUTPUT"))
77        return -1;
78    if (runIptablesCmd("-P FORWARD DROP"))
79        return -1;
80    if (runIptablesCmd("-F FORWARD"))
81        return -1;
82    if (runIptablesCmd("-t nat -F"))
83        return -1;
84    return 0;
85}
86
87bool NatController::interfaceExists(const char *iface) {
88    // XXX: Implement this
89    return true;
90}
91
92int NatController::doNatCommands(const char *intIface, const char *extIface, bool add) {
93    char cmd[255];
94
95    // handle decrement to 0 case (do reset to defaults) and erroneous dec below 0
96    if (add == false) {
97        if (natCount <= 1) {
98            int ret = setDefaults();
99            if (ret == 0) {
100                natCount=0;
101            }
102            return ret;
103        }
104    }
105
106    if (!interfaceExists(intIface) || !interfaceExists (extIface)) {
107        LOGE("Invalid interface specified");
108        errno = ENODEV;
109        return -1;
110    }
111
112    snprintf(cmd, sizeof(cmd),
113             "-%s FORWARD -i %s -o %s -m state --state ESTABLISHED,RELATED -j ACCEPT",
114             (add ? "A" : "D"),
115             extIface, intIface);
116    if (runIptablesCmd(cmd)) {
117        return -1;
118    }
119
120    snprintf(cmd, sizeof(cmd), "-%s FORWARD -i %s -o %s -j ACCEPT", (add ? "A" : "D"),
121            intIface, extIface);
122    if (runIptablesCmd(cmd)) {
123        // unwind what's been done, but don't care about success - what more could we do?
124        snprintf(cmd, sizeof(cmd),
125                 "-%s FORWARD -i %s -o %s -m state --state ESTABLISHED,RELATED -j ACCEPT",
126                 (!add ? "A" : "D"),
127                 extIface, intIface);
128        return -1;
129    }
130
131    // add this if we are the first added nat
132    if (add && natCount == 0) {
133        snprintf(cmd, sizeof(cmd), "-t nat -A POSTROUTING -o %s -j MASQUERADE", extIface);
134        if (runIptablesCmd(cmd)) {
135            // unwind what's been done, but don't care about success - what more could we do?
136            setDefaults();;
137            return -1;
138        }
139    }
140
141    if (add) {
142        natCount++;
143    } else {
144        natCount--;
145    }
146    return 0;
147}
148
149int NatController::enableNat(const char *intIface, const char *extIface) {
150    return doNatCommands(intIface, extIface, true);
151}
152
153int NatController::disableNat(const char *intIface, const char *extIface) {
154    return doNatCommands(intIface, extIface, false);
155}
156