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// SPDX-License-Identifier: GPL-2.0-only
/*
* Copyright (c) 2018 Jann Horn <jannh@google.com>
* Copyright (c) 2020 SUSE LLC <mdoucha@suse.cz>
*/
/*
* CVE 2018-18445
*
* Check that eBPF verifier correctly handles 32-bit arithmetic, in particular
* the right bit shift instruction. It is an error if the BPF program passes
* verification regardless of whether it then causes any actual damage. Kernel
* bug fixed in:
*
* commit b799207e1e1816b09e7a5920fbb2d5fcf6edd681
* Author: Jann Horn <jannh@google.com>
* Date: Fri Oct 5 18:17:59 2018 +0200
*
* bpf: 32-bit RSH verification must truncate input before the ALU op
*/
#include <stdio.h>
#include <string.h>
#include "config.h"
#include "tst_test.h"
#include "tst_taint.h"
#include "tst_capability.h"
#include "bpf_common.h"
#define BUFSIZE 8192
#define CHECK_BPF_RET(x) ((x) >= 0 || ((x) == -1 && errno != EACCES))
static const char MSG[] = "Ahoj!";
static char *msg;
static char *log;
static union bpf_attr *attr;
static int load_prog(int fd)
{
int ret;
struct bpf_insn insn[] = {
BPF_MOV64_IMM(BPF_REG_8, 2),
BPF_ALU64_IMM(BPF_LSH, BPF_REG_8, 31),
BPF_ALU32_IMM(BPF_RSH, BPF_REG_8, 31),
BPF_ALU32_IMM(BPF_SUB, BPF_REG_8, 2),
// store r8 into map
BPF_LD_MAP_FD(BPF_REG_1, fd),
BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -4),
BPF_ST_MEM(BPF_W, BPF_REG_2, 0, 0),
BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem),
BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 1),
BPF_EXIT_INSN(),
BPF_ALU64_REG(BPF_ADD, BPF_REG_0, BPF_REG_8),
BPF_STX_MEM(BPF_DW, BPF_REG_0, BPF_REG_8, 0),
BPF_MOV64_IMM(BPF_REG_0, 0),
BPF_EXIT_INSN()
};
bpf_init_prog_attr(attr, insn, sizeof(insn), log, BUFSIZE);
ret = TST_RETRY_FUNC(bpf(BPF_PROG_LOAD, attr, sizeof(*attr)),
CHECK_BPF_RET);
if (ret >= 0) {
tst_res(TINFO, "Verification log:");
fputs(log, stderr);
return ret;
}
if (ret < -1)
tst_brk(TBROK, "Invalid bpf() return value %d", ret);
if (!*log)
tst_brk(TBROK | TERRNO, "Failed to load BPF program");
tst_res(TPASS | TERRNO, "BPF program failed verification");
return ret;
}
static void setup(void)
{
rlimit_bump_memlock();
memcpy(msg, MSG, sizeof(MSG));
}
static void run(void)
{
int map_fd, prog_fd;
map_fd = bpf_map_array_create(1);
prog_fd = load_prog(map_fd);
if (prog_fd >= 0) {
tst_res(TFAIL, "Malicious eBPF code passed verification. "
"Now let's try crashing the kernel.");
bpf_run_prog(prog_fd, msg, sizeof(MSG));
}
if (prog_fd >= 0)
SAFE_CLOSE(prog_fd);
SAFE_CLOSE(map_fd);
}
static struct tst_test test = {
.setup = setup,
.test_all = run,
.min_kver = "3.18",
.taint_check = TST_TAINT_W | TST_TAINT_D,
.caps = (struct tst_cap []) {
TST_CAP(TST_CAP_DROP, CAP_SYS_ADMIN),
{}
},
.bufs = (struct tst_buffers []) {
{&log, .size = BUFSIZE},
{&attr, .size = sizeof(*attr)},
{&msg, .size = sizeof(MSG)},
{}
},
.tags = (const struct tst_tag[]) {
{"linux-git", "b799207e1e18"},
{"CVE", "2018-18445"},
{}
}
};
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