blob: c69c347c7011296a477a8ffaff8123b956901556 [file] [log] [blame]
Will Drewry8ac270d2012-04-12 16:48:04 -05001/*
2 * Naive system call dropper built on seccomp_filter.
3 *
4 * Copyright (c) 2012 The Chromium OS Authors <chromium-os-dev@chromium.org>
5 * Author: Will Drewry <wad@chromium.org>
6 *
7 * The code may be used by anyone for any purpose,
8 * and can serve as a starting point for developing
9 * applications using prctl(PR_SET_SECCOMP, 2, ...).
10 *
11 * When run, returns the specified errno for the specified
12 * system call number against the given architecture.
13 *
14 * Run this one as root as PR_SET_NO_NEW_PRIVS is not called.
15 */
16
17#include <errno.h>
18#include <linux/audit.h>
19#include <linux/filter.h>
20#include <linux/seccomp.h>
21#include <linux/unistd.h>
22#include <stdio.h>
23#include <stddef.h>
24#include <stdlib.h>
25#include <sys/prctl.h>
26#include <unistd.h>
27
28static int install_filter(int nr, int arch, int error)
29{
30 struct sock_filter filter[] = {
31 BPF_STMT(BPF_LD+BPF_W+BPF_ABS,
32 (offsetof(struct seccomp_data, arch))),
33 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, arch, 0, 3),
34 BPF_STMT(BPF_LD+BPF_W+BPF_ABS,
35 (offsetof(struct seccomp_data, nr))),
36 BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, nr, 0, 1),
37 BPF_STMT(BPF_RET+BPF_K,
38 SECCOMP_RET_ERRNO|(error & SECCOMP_RET_DATA)),
39 BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW),
40 };
41 struct sock_fprog prog = {
42 .len = (unsigned short)(sizeof(filter)/sizeof(filter[0])),
43 .filter = filter,
44 };
45 if (prctl(PR_SET_SECCOMP, 2, &prog)) {
46 perror("prctl");
47 return 1;
48 }
49 return 0;
50}
51
52int main(int argc, char **argv)
53{
54 if (argc < 5) {
55 fprintf(stderr, "Usage:\n"
56 "dropper <syscall_nr> <arch> <errno> <prog> [<args>]\n"
57 "Hint: AUDIT_ARCH_I386: 0x%X\n"
58 " AUDIT_ARCH_X86_64: 0x%X\n"
59 "\n", AUDIT_ARCH_I386, AUDIT_ARCH_X86_64);
60 return 1;
61 }
62 if (install_filter(strtol(argv[1], NULL, 0), strtol(argv[2], NULL, 0),
63 strtol(argv[3], NULL, 0)))
64 return 1;
65 execv(argv[4], &argv[4]);
66 printf("Failed to execv\n");
67 return 255;
68}