1*4882a593Smuzhiyun // SPDX-License-Identifier: GPL-2.0
2*4882a593Smuzhiyun /*
3*4882a593Smuzhiyun * Naive system call dropper built on seccomp_filter.
4*4882a593Smuzhiyun *
5*4882a593Smuzhiyun * Copyright (c) 2012 The Chromium OS Authors <chromium-os-dev@chromium.org>
6*4882a593Smuzhiyun * Author: Will Drewry <wad@chromium.org>
7*4882a593Smuzhiyun *
8*4882a593Smuzhiyun * The code may be used by anyone for any purpose,
9*4882a593Smuzhiyun * and can serve as a starting point for developing
10*4882a593Smuzhiyun * applications using prctl(PR_SET_SECCOMP, 2, ...).
11*4882a593Smuzhiyun *
12*4882a593Smuzhiyun * When run, returns the specified errno for the specified
13*4882a593Smuzhiyun * system call number against the given architecture.
14*4882a593Smuzhiyun *
15*4882a593Smuzhiyun */
16*4882a593Smuzhiyun
17*4882a593Smuzhiyun #include <errno.h>
18*4882a593Smuzhiyun #include <linux/audit.h>
19*4882a593Smuzhiyun #include <linux/filter.h>
20*4882a593Smuzhiyun #include <linux/seccomp.h>
21*4882a593Smuzhiyun #include <linux/unistd.h>
22*4882a593Smuzhiyun #include <stdio.h>
23*4882a593Smuzhiyun #include <stddef.h>
24*4882a593Smuzhiyun #include <stdlib.h>
25*4882a593Smuzhiyun #include <sys/prctl.h>
26*4882a593Smuzhiyun #include <unistd.h>
27*4882a593Smuzhiyun
install_filter(int nr,int arch,int error)28*4882a593Smuzhiyun static int install_filter(int nr, int arch, int error)
29*4882a593Smuzhiyun {
30*4882a593Smuzhiyun struct sock_filter filter[] = {
31*4882a593Smuzhiyun BPF_STMT(BPF_LD+BPF_W+BPF_ABS,
32*4882a593Smuzhiyun (offsetof(struct seccomp_data, arch))),
33*4882a593Smuzhiyun BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, arch, 0, 3),
34*4882a593Smuzhiyun BPF_STMT(BPF_LD+BPF_W+BPF_ABS,
35*4882a593Smuzhiyun (offsetof(struct seccomp_data, nr))),
36*4882a593Smuzhiyun BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, nr, 0, 1),
37*4882a593Smuzhiyun BPF_STMT(BPF_RET+BPF_K,
38*4882a593Smuzhiyun SECCOMP_RET_ERRNO|(error & SECCOMP_RET_DATA)),
39*4882a593Smuzhiyun BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW),
40*4882a593Smuzhiyun };
41*4882a593Smuzhiyun struct sock_fprog prog = {
42*4882a593Smuzhiyun .len = (unsigned short)(sizeof(filter)/sizeof(filter[0])),
43*4882a593Smuzhiyun .filter = filter,
44*4882a593Smuzhiyun };
45*4882a593Smuzhiyun if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
46*4882a593Smuzhiyun perror("prctl(NO_NEW_PRIVS)");
47*4882a593Smuzhiyun return 1;
48*4882a593Smuzhiyun }
49*4882a593Smuzhiyun if (prctl(PR_SET_SECCOMP, 2, &prog)) {
50*4882a593Smuzhiyun perror("prctl(PR_SET_SECCOMP)");
51*4882a593Smuzhiyun return 1;
52*4882a593Smuzhiyun }
53*4882a593Smuzhiyun return 0;
54*4882a593Smuzhiyun }
55*4882a593Smuzhiyun
main(int argc,char ** argv)56*4882a593Smuzhiyun int main(int argc, char **argv)
57*4882a593Smuzhiyun {
58*4882a593Smuzhiyun if (argc < 5) {
59*4882a593Smuzhiyun fprintf(stderr, "Usage:\n"
60*4882a593Smuzhiyun "dropper <syscall_nr> <arch> <errno> <prog> [<args>]\n"
61*4882a593Smuzhiyun "Hint: AUDIT_ARCH_I386: 0x%X\n"
62*4882a593Smuzhiyun " AUDIT_ARCH_X86_64: 0x%X\n"
63*4882a593Smuzhiyun "\n", AUDIT_ARCH_I386, AUDIT_ARCH_X86_64);
64*4882a593Smuzhiyun return 1;
65*4882a593Smuzhiyun }
66*4882a593Smuzhiyun if (install_filter(strtol(argv[1], NULL, 0), strtol(argv[2], NULL, 0),
67*4882a593Smuzhiyun strtol(argv[3], NULL, 0)))
68*4882a593Smuzhiyun return 1;
69*4882a593Smuzhiyun execv(argv[4], &argv[4]);
70*4882a593Smuzhiyun printf("Failed to execv\n");
71*4882a593Smuzhiyun return 255;
72*4882a593Smuzhiyun }
73