Documentation: prctl/seccomp_filter
[linux-3.10.git] / samples / seccomp / dropper.c
1 /*
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
28 static 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
52 int 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 }