File: enosys.c

package info (click to toggle)
util-linux 2.41-5
  • links: PTS, VCS
  • area: main
  • in suites: sid, trixie
  • size: 95,208 kB
  • sloc: ansic: 179,016; sh: 22,689; yacc: 1,284; makefile: 528; xml: 422; python: 316; lex: 89; ruby: 75; csh: 37; exp: 19; sed: 16; perl: 15; sql: 9
file content (306 lines) | stat: -rw-r--r-- 8,928 bytes parent folder | download | duplicates (2)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
/*
 * Copyright (C) 2023 Thomas Weißschuh <thomas@t-8ch.de>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it would be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

#include <stddef.h>
#include <stdbool.h>
#include <getopt.h>

#include <linux/unistd.h>
#include <linux/audit.h>
#include <sys/prctl.h>
#include <sys/syscall.h>
#include <sys/ioctl.h>

#include "c.h"
#include "exitcodes.h"
#include "nls.h"
#include "bitops.h"
#include "audit-arch.h"
#include "list.h"
#include "xalloc.h"
#include "strutils.h"
#include "seccomp.h"
#include "all-io.h"

#define IS_LITTLE_ENDIAN (__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__)

#define syscall_nr (offsetof(struct seccomp_data, nr))
#define syscall_arch (offsetof(struct seccomp_data, arch))
#define _syscall_arg(n) (offsetof(struct seccomp_data, args[n]))
#define syscall_arg_lower32(n) (_syscall_arg(n) + 4 * !IS_LITTLE_ENDIAN)
#define syscall_arg_upper32(n) (_syscall_arg(n) + 4 * IS_LITTLE_ENDIAN)

struct syscall {
	const char *const name;
	long number;
};

/* When the alias arrays are empty the compiler emits -Wtype-limits warnings.
 * Avoid those by going through this function. */
static inline bool lt(size_t a, size_t b)
{
	return a < b;
}

static const struct syscall syscalls[] = {
#define UL_SYSCALL(name, nr) { name, nr },
#include "syscalls.h"
#undef UL_SYSCALL
};

static const struct syscall errnos[] = {
#define UL_ERRNO(name, nr) { name, nr },
#include "errnos.h"
#undef UL_ERRNO
};

static const struct syscall ioctls[] = {
	{ "FIOCLEX", FIOCLEX },
};

static void __attribute__((__noreturn__)) usage(void)
{
	FILE *out = stdout;

	fputs(USAGE_HEADER, out);
	fprintf(out, _(" %s [options] -- <command>\n"), program_invocation_short_name);

	fputs(USAGE_OPTIONS, out);
	fputs(_(" -s, --syscall           syscall to block\n"), out);
	fputs(_(" -i, --ioctl             ioctl to block\n"), out);
	fputs(_(" -l, --list              list known syscalls\n"), out);
	fputs(_(" -d, --dump[=<file>]     dump seccomp bytecode\n"), out);

	fputs(USAGE_SEPARATOR, out);
	fprintf(out, USAGE_HELP_OPTIONS(25));

	fprintf(out, USAGE_MAN_TAIL("enosys(1)"));

	exit(EXIT_SUCCESS);
}

struct blocked_number {
	struct list_head head;
	long number;
	int ret;
};

static struct blocked_number *parse_block(const char *s, int ret, const struct syscall entities[], size_t n_entities)
{
	struct blocked_number *blocked;
	const char *name, *error_name;
	long blocked_number;
	char *colon;
	bool found;
	size_t i;

	colon = strchr(s, ':');
	if (colon) {
		name = xstrndup(s, colon - s);
		error_name = colon + 1;

		found = 0;
		for (i = 0; i < ARRAY_SIZE(errnos); i++) {
			if (strcmp(error_name, errnos[i].name) == 0) {
				ret = errnos[i].number;
				found = 1;
				break;
			}
		}
		if (!found)
			ret = str2num_or_err(
					colon + 1, 10, _("Unknown errno"), 0, INT_MAX);
	} else {
		name = s;
	}

	found = 0;
	for (i = 0; i < n_entities; i++) {
		if (strcmp(name, entities[i].name) == 0) {
			blocked_number = entities[i].number;
			found = 1;
			break;
		}
	}
	if (!found)
		blocked_number = str2num_or_err(
				name, 10, _("Unknown syscall"), 0, LONG_MAX);

	blocked = xmalloc(sizeof(*blocked));
	blocked->number = blocked_number;
	blocked->ret = ret;

	if (name != s)
		free((char *)name);

	return blocked;
}

int main(int argc, char **argv)
{
	int c;
	size_t i;
	FILE *dump = NULL;
	static const struct option longopts[] = {
		{ "syscall",    required_argument, NULL, 's' },
		{ "ioctl",      required_argument, NULL, 'i' },
		{ "list",       no_argument,       NULL, 'l' },
		{ "list-ioctl", no_argument,       NULL, 'm' },
		{ "dump",       optional_argument, NULL, 'd' },
		{ "version",    no_argument,       NULL, 'V' },
		{ "help",       no_argument,       NULL, 'h' },
		{ 0 }
	};

	struct blocked_number *blocked;
	struct list_head *loop_ctr;
	struct list_head blocked_syscalls;
	bool blocking_execve = false;
	INIT_LIST_HEAD(&blocked_syscalls);
	struct list_head blocked_ioctls;
	INIT_LIST_HEAD(&blocked_ioctls);

	setlocale(LC_ALL, "");
	bindtextdomain(PACKAGE, LOCALEDIR);
	textdomain(PACKAGE);

	while ((c = getopt_long (argc, argv, "+Vhs:i:lmd::", longopts, NULL)) != -1) {
		switch (c) {
		case 's':
			blocked = parse_block(optarg, ENOSYS, syscalls, ARRAY_SIZE(syscalls));
			list_add(&blocked->head, &blocked_syscalls);
			if (blocked->number == __NR_execve)
				blocking_execve = true;

			break;
		case 'i':
			blocked = parse_block(optarg, ENOTTY, ioctls, ARRAY_SIZE(ioctls));
			list_add(&blocked->head, &blocked_ioctls);

			break;
		case 'l':
			for (i = 0; lt(i, ARRAY_SIZE(syscalls)); i++)
				printf("%5ld %s\n", syscalls[i].number, syscalls[i].name);
			return EXIT_SUCCESS;
		case 'm':
			for (i = 0; lt(i, ARRAY_SIZE(ioctls)); i++)
				printf("%5ld %s\n", ioctls[i].number, ioctls[i].name);
			return EXIT_SUCCESS;
		case 'd':
			if (optarg) {
				if (*optarg == '=')
					optarg++;
				dump = fopen(optarg, "w");
				if (!dump)
					err(EXIT_FAILURE, _("Could not open %s"), optarg);
			} else {
				dump = stdout;
			}
			break;
		case 'V':
			print_version(EXIT_SUCCESS);
		case 'h':
			usage();
		default:
			errtryhelp(EXIT_FAILURE);
		}
	}

	if (!dump && optind >= argc)
		errtryhelp(EXIT_FAILURE);

	struct sock_filter filter[BPF_MAXINSNS];
	struct sock_filter *f = filter;

#define INSTR(_instruction)                                        \
	if (f == &filter[ARRAY_SIZE(filter)])                      \
		errx(EXIT_FAILURE, _("filter too big")); \
	*f++ = (struct sock_filter) _instruction

	INSTR(BPF_STMT(BPF_LD | BPF_W | BPF_ABS, syscall_arch));
	INSTR(BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, SECCOMP_ARCH_NATIVE, 1, 0));
	INSTR(BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_TRAP));

	/* Blocking "execve" normally would also block our own call to
	 * it and the end of main. To distinguish between our execve
	 * and the execve to be blocked, compare the environ pointer.
	 *
	 * See https://lore.kernel.org/all/CAAnLoWnS74dK9Wq4EQ-uzQ0qCRfSK-dLqh+HCais-5qwDjrVzg@mail.gmail.com/
	 */
	if (blocking_execve) {
		INSTR(BPF_STMT(BPF_LD | BPF_W | BPF_ABS, syscall_nr));
		INSTR(BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, __NR_execve, 0, 5));
		INSTR(BPF_STMT(BPF_LD | BPF_W | BPF_ABS, syscall_arg_lower32(2)));
		INSTR(BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, (uint64_t)(uintptr_t) environ, 0, 3));
		INSTR(BPF_STMT(BPF_LD | BPF_W | BPF_ABS, syscall_arg_upper32(2)));
		INSTR(BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, (uint64_t)(uintptr_t) environ >> 32, 0, 1));
		INSTR(BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW));
	}

	INSTR(BPF_STMT(BPF_LD | BPF_W | BPF_ABS, syscall_nr));

	list_for_each(loop_ctr, &blocked_syscalls) {
		blocked = list_entry(loop_ctr, struct blocked_number, head);

		INSTR(BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, blocked->number, 0, 1));
		INSTR(BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ERRNO | blocked->ret));
	}

	if (!list_empty(&blocked_ioctls)) {
		INSTR(BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, __NR_ioctl, 1, 0));
		INSTR(BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW));

		list_for_each(loop_ctr, &blocked_ioctls) {
			blocked = list_entry(loop_ctr, struct blocked_number, head);

			INSTR(BPF_STMT(BPF_LD | BPF_W | BPF_ABS, syscall_arg_lower32(1)));
			INSTR(BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, (uint64_t) blocked->number, 0, 3));
			INSTR(BPF_STMT(BPF_LD | BPF_W | BPF_ABS, syscall_arg_upper32(1)));
			INSTR(BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, (uint64_t) blocked->number >> 32, 0, 1));
			INSTR(BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ERRNO | blocked->ret));
		}
	}

	INSTR(BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW));

	if (dump) {
		if (fwrite_all(filter, (f - filter) * sizeof(filter[0]), 1, dump))
			err(EXIT_FAILURE, _("Could not dump seccomp filter"));
		return EXIT_SUCCESS;
	}

	struct sock_fprog prog = {
		.len    = f - filter,
		.filter = filter,
	};

	/* *SET* below will return EINVAL when either the filter is invalid or
	 * seccomp is not supported. To distinguish those cases do a *GET* here
	 */
	if (prctl(PR_GET_SECCOMP) == -1 && errno == EINVAL)
		err(EXIT_NOTSUPP, _("Seccomp non-functional"));

	if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0))
		err_nosys(EXIT_FAILURE, _("Could not run prctl(PR_SET_NO_NEW_PRIVS)"));

	if (ul_set_seccomp_filter_spec_allow(&prog))
		err_nosys(EXIT_FAILURE, _("Could not seccomp filter"));

	if (execvp(argv[optind], argv + optind))
		err(EXIT_NOTSUPP, _("Could not exec"));
}