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 */
15
16#include <errno.h>
17#include <linux/audit.h>
18#include <linux/filter.h>
19#include <linux/seccomp.h>
20#include <linux/unistd.h>
21#include <stdio.h>
22#include <stddef.h>
23#include <stdlib.h>
24#include <sys/prctl.h>
25#include <unistd.h>
26
27static int install_filter(int nr, int arch, int error)
28{
29	struct sock_filter filter[] = {
30		BPF_STMT(BPF_LD+BPF_W+BPF_ABS,
31			 (offsetof(struct seccomp_data, arch))),
32		BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, arch, 0, 3),
33		BPF_STMT(BPF_LD+BPF_W+BPF_ABS,
34			 (offsetof(struct seccomp_data, nr))),
35		BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, nr, 0, 1),
36		BPF_STMT(BPF_RET+BPF_K,
37			 SECCOMP_RET_ERRNO|(error & SECCOMP_RET_DATA)),
38		BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW),
39	};
40	struct sock_fprog prog = {
41		.len = (unsigned short)(sizeof(filter)/sizeof(filter[0])),
42		.filter = filter,
43	};
 
 
 
 
44	if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
45		perror("prctl(NO_NEW_PRIVS)");
46		return 1;
47	}
48	if (prctl(PR_SET_SECCOMP, 2, &prog)) {
49		perror("prctl(PR_SET_SECCOMP)");
50		return 1;
51	}
52	return 0;
53}
54
55int main(int argc, char **argv)
56{
57	if (argc < 5) {
58		fprintf(stderr, "Usage:\n"
59			"dropper <syscall_nr> <arch> <errno> <prog> [<args>]\n"
60			"Hint:	AUDIT_ARCH_I386: 0x%X\n"
61			"	AUDIT_ARCH_X86_64: 0x%X\n"
 
62			"\n", AUDIT_ARCH_I386, AUDIT_ARCH_X86_64);
63		return 1;
64	}
65	if (install_filter(strtol(argv[1], NULL, 0), strtol(argv[2], NULL, 0),
66			   strtol(argv[3], NULL, 0)))
67		return 1;
68	execv(argv[4], &argv[4]);
69	printf("Failed to execv\n");
70	return 255;
71}

 1// SPDX-License-Identifier: GPL-2.0
 2/*
 3 * Naive system call dropper built on seccomp_filter.
 4 *
 5 * Copyright (c) 2012 The Chromium OS Authors <chromium-os-dev@chromium.org>
 6 * Author: Will Drewry <wad@chromium.org>
 7 *
 8 * The code may be used by anyone for any purpose,
 9 * and can serve as a starting point for developing
10 * applications using prctl(PR_SET_SECCOMP, 2, ...).
11 *
12 * When run, returns the specified errno for the specified
13 * system call number against the given architecture.
14 *
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 arch, int nr, 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 (error == -1) {
46		struct sock_filter kill = BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_KILL);
47		filter[4] = kill;
48	}
49	if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
50		perror("prctl(NO_NEW_PRIVS)");
51		return 1;
52	}
53	if (prctl(PR_SET_SECCOMP, 2, &prog)) {
54		perror("prctl(PR_SET_SECCOMP)");
55		return 1;
56	}
57	return 0;
58}
59
60int main(int argc, char **argv)
61{
62	if (argc < 5) {
63		fprintf(stderr, "Usage:\n"
64			"dropper <arch> <syscall_nr> <errno> <prog> [<args>]\n"
65			"Hint:	AUDIT_ARCH_I386: 0x%X\n"
66			"	AUDIT_ARCH_X86_64: 0x%X\n"
67			"	errno == -1 means SECCOMP_RET_KILL\n"
68			"\n", AUDIT_ARCH_I386, AUDIT_ARCH_X86_64);
69		return 1;
70	}
71	if (install_filter(strtol(argv[1], NULL, 0), strtol(argv[2], NULL, 0),
72			   strtol(argv[3], NULL, 0)))
73		return 1;
74	execv(argv[4], &argv[4]);
75	printf("Failed to execv\n");
76	return 255;
77}