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/*
* Copyright (C) 2023 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
*/
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <fcntl.h>
#include <dlfcn.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <linux/if.h>
#include <linux/if_tun.h>
#include <android/log.h>
#include "zygisk.hpp"
using zygisk::Api;
using zygisk::ServerSpecializeArgs;
static const char *package_whitelist[] = {
"com.wireguard.android",
"com.wireguard.android.debug",
};
#define LOG_TAG "WireGuard/TunFlags"
#define ALOGE(...) __android_log_print(ANDROID_LOG_ERROR, LOG_TAG, __VA_ARGS__)
#define ALOGI(...) __android_log_print(ANDROID_LOG_INFO, LOG_TAG, __VA_ARGS__)
static bool is_wireguard(JNIEnv *env, jobject vpn_obj)
{
jclass clazz = env->GetObjectClass(vpn_obj);
if (!clazz) {
ALOGE("Could not determine class of VPN object");
return false;
}
jfieldID package_field = env->GetFieldID(clazz, "mPackage", "Ljava/lang/String;");
if (!package_field) {
ALOGE("Could not find package field ID");
return false;
}
jstring package_obj = static_cast<jstring>(env->GetObjectField(vpn_obj, package_field));
if (!package_obj) {
ALOGE("Could not get package field");
return false;
}
const char *package = env->GetStringUTFChars(package_obj, NULL);
bool ret = false;
for (size_t i = 0; i < sizeof(package_whitelist) / sizeof(*package_whitelist); ++i) {
if (!strcmp(package_whitelist[i], package)) {
ret = true;
break;
}
}
env->ReleaseStringUTFChars(package_obj, package);
return ret;
}
static jint(*orig_create)(JNIEnv *, jobject, jint);
/* Reimplementation of https://cs.android.com/android/platform/superproject/main/+/main:frameworks/base/services/core/jni/com_android_server_connectivity_Vpn.cpp;l=59;drc=586d0eb1fef2114f01606f4275043abc0f40ff0b */
static jint create(JNIEnv *env, jobject thiz, jint mtu)
{
if (!is_wireguard(env, thiz))
return orig_create(env, thiz, mtu);
ALOGI("Using hooked function to create IFF_VNET_HDR tun device");
int tun = open("/dev/tun", O_RDWR | O_NONBLOCK | O_CLOEXEC);
if (tun < 0) {
ALOGE("Cannot allocate TUN: %s", strerror(errno));
return -1;
}
/* Allocate interface */
ifreq ifr4 = { 0 };
ifr4.ifr_flags = IFF_TUN | IFF_NO_PI | IFF_VNET_HDR;
if (ioctl(tun, TUNSETIFF, &ifr4) < 0) {
ALOGE("Cannot allocate TUN: %s", strerror(errno));
goto error;
}
/* Activate interface */
static int inet4 = socket(AF_INET, SOCK_DGRAM | SOCK_CLOEXEC, 0);
ifr4.ifr_flags = IFF_UP;
if (ioctl(inet4, SIOCSIFFLAGS, &ifr4) < 0) {
ALOGE("Cannot activate %s: %s", ifr4.ifr_name, strerror(errno));
goto error;
}
/* Set MTU if it is specified */
ifr4.ifr_mtu = mtu;
if (mtu > 0 && ioctl(inet4, SIOCSIFMTU, &ifr4) < 0) {
ALOGE("Cannot set MTU on %s: %s", ifr4.ifr_name, strerror(errno));
goto error;
}
return tun;
error:
close(tun);
return -1;
}
static jint(*orig_register_natives)(JNIEnv *, jclass, const JNINativeMethod *, jint);
static jint register_natives(JNIEnv *env, jclass clazz, const JNINativeMethod *methods, jint num_methods)
{
static jmethodID class_getname = env->GetMethodID(env->FindClass("java/lang/Class"), "getName", "()Ljava/lang/String;");
jstring name_string = static_cast<jstring>(env->CallObjectMethod(clazz, class_getname));
const char *name = env->GetStringUTFChars(name_string, nullptr);
bool is_vpn = !strcmp(name, "com.android.server.connectivity.Vpn");
env->ReleaseStringUTFChars(name_string, name);
if (!is_vpn)
goto out;
for (jint i = 0; i < num_methods; ++i) {
if (strcmp(methods[i].name, "jniCreate"))
continue;
orig_create = reinterpret_cast<decltype(orig_create)>(methods[i].fnPtr);
JNINativeMethod *new_methods = new JNINativeMethod[num_methods];
memcpy(new_methods, methods, num_methods * sizeof(*new_methods));
new_methods[i].fnPtr = reinterpret_cast<decltype(new_methods[i].fnPtr)>(create);
methods = new_methods;
break;
}
out:
return orig_register_natives(env, clazz, methods, num_methods);
}
class TunFlags : public zygisk::ModuleBase
{
public:
void onLoad(Api *api, JNIEnv *env) override
{
this->api = api;
this->env = env;
}
void postServerSpecialize(const ServerSpecializeArgs *args) override
{
orig_register_natives = env->functions->RegisterNatives;
JNINativeInterface *new_functions = new JNINativeInterface;
*new_functions = *env->functions;
new_functions->RegisterNatives = register_natives;
env->functions = new_functions;
}
private:
Api *api;
JNIEnv *env;
};
REGISTER_ZYGISK_MODULE(TunFlags)
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