159 lines
3.8 KiB
C
159 lines
3.8 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* Copyright (c) 2022 SUSE LLC <rpalethorpe@suse.com>
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*/
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/*\
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* [Description]
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*
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* ringbuf_submit takes a pointer to a ringbuf record, but not the
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* size of this record. The verifier only validates offset ptrs[1] passed
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* to functions if the function has a size parameter. So we can
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* perform a wide range of ptr arithmetic on this record ptr.
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*
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* ringbuf_submit updates some data (i.e. the length) in the
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* ringbuf header which is calculated from the record ptr. So this can
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* be used to corrupt memory.
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*
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* This test does not try to cause a crash. Howver it does run the
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* eBPF if it can. This will result in an instant crash or memory
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* corruption which may later cause a crash.
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*
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* This test is adapted from a full reproducer which can be found here:
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* https://github.com/tr3ee/CVE-2021-4204
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*
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* It's recommended to disable unprivileged eBPF by setting
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* /proc/sys/kernel/unprivileged_bpf_disabled. Also there is a
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* specific fix for this issue:
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*
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* commit 64620e0a1e712a778095bd35cbb277dc2259281f
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* Author: Daniel Borkmann <daniel@iogearbox.net>
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* Date: Tue Jan 11 14:43:41 2022 +0000
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*
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* bpf: Fix out of bounds access for ringbuf helpers
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*
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* [1]: Depending on the ptr/reg type
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*/
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#include <stdio.h>
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#include <string.h>
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#include <inttypes.h>
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#include "config.h"
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#include "tst_test.h"
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#include "tst_taint.h"
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#include "tst_capability.h"
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#include "lapi/bpf.h"
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#include "bpf_common.h"
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#define BUFSIZE 8192
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static const char MSG[] = "Ahoj!";
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static char *msg;
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static int map_fd;
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static uint32_t *key;
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static uint64_t *val;
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static char *log;
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static union bpf_attr *attr;
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static int load_prog(void)
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{
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int ret;
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const struct bpf_insn prog_insn[] = {
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// r0 = bpf_ringbuf_reserve(ctx->ringbuf_fd, 0xff0, 0)
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BPF_LD_MAP_FD(BPF_REG_1, map_fd),
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BPF_MOV64_IMM(BPF_REG_2, 0xff0),
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BPF_MOV64_IMM(BPF_REG_3, 0x00),
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BPF_EMIT_CALL(BPF_FUNC_ringbuf_reserve),
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// if (r0 == NULL) exit(2)
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BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 2),
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BPF_MOV64_IMM(BPF_REG_0, 2),
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BPF_EXIT_INSN(),
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// r0 = BPF_FUNC_ringbuf_submit(r0-(0x3008-0x38), BPF_RB_NO_WAKEUP)
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BPF_ALU64_IMM(BPF_SUB, BPF_REG_0, (0x3008-0x38)),
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BPF_MOV64_REG(BPF_REG_1, BPF_REG_0),
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BPF_MOV64_IMM(BPF_REG_2, 1),
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BPF_EMIT_CALL(BPF_FUNC_ringbuf_submit),
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/* exit(0) */
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BPF_MOV64_IMM(BPF_REG_0, 0),
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BPF_EXIT_INSN()
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};
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bpf_init_prog_attr(attr, prog_insn, sizeof(prog_insn), log, BUFSIZE);
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ret = TST_RETRY_FUNC(bpf(BPF_PROG_LOAD, attr, sizeof(*attr)),
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TST_RETVAL_GE0);
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if (ret >= 0)
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return ret;
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if (ret != -1)
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tst_brk(TBROK, "Invalid bpf() return value: %d", ret);
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if (log[0] != 0)
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tst_printf("%s\n", log);
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return ret;
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}
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static void setup(void)
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{
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rlimit_bump_memlock();
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memcpy(msg, MSG, sizeof(MSG));
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}
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static void run(void)
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{
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int prog_fd;
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map_fd = bpf_map_create(&(union bpf_attr){
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.map_type = BPF_MAP_TYPE_RINGBUF,
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.key_size = 0,
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.value_size = 0,
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.max_entries = getpagesize()
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});
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tst_res(TINFO, "Trying to load eBPF with OOB write");
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prog_fd = load_prog();
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if (prog_fd == -1) {
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tst_res(TPASS, "Failed verification");
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return;
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}
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tst_res(TFAIL, "Loaded program with OOB write");
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tst_res(TINFO, "Running eBPF with OOB");
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bpf_run_prog(prog_fd, msg, sizeof(MSG));
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tst_res(TINFO, "Ran eBPF");
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SAFE_CLOSE(prog_fd);
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}
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static struct tst_test test = {
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.setup = setup,
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.test_all = run,
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.min_kver = "5.8",
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.taint_check = TST_TAINT_W | TST_TAINT_D,
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.caps = (struct tst_cap []) {
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TST_CAP(TST_CAP_DROP, CAP_SYS_ADMIN),
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TST_CAP(TST_CAP_DROP, CAP_BPF),
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{}
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},
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.bufs = (struct tst_buffers []) {
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{&key, .size = sizeof(*key)},
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{&val, .size = sizeof(*val)},
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{&log, .size = BUFSIZE},
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{&attr, .size = sizeof(*attr)},
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{&msg, .size = sizeof(MSG)},
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{}
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},
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.tags = (const struct tst_tag[]) {
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{"linux-git", "64620e0a1e71"},
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{"CVE", "CVE-2021-4204"},
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{}
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}
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};
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