1/* $OpenBSD: sandbox-systrace.c,v 1.14 2015/01/20 23:14:00 deraadt Exp $ */
2/*
3 * Copyright (c) 2011 Damien Miller <djm@mindrot.org>
4 *
5 * Permission to use, copy, modify, and distribute this software for any
6 * purpose with or without fee is hereby granted, provided that the above
7 * copyright notice and this permission notice appear in all copies.
8 *
9 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
10 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
11 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
12 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
13 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
14 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
15 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
16 */
17
18#include "includes.h"
19
20#ifdef SANDBOX_SYSTRACE
21
22#include <sys/types.h>
23#include <sys/ioctl.h>
24#include <sys/syscall.h>
25#include <sys/socket.h>
26#include <sys/wait.h>
27
28#include <dev/systrace.h>
29
30#include <errno.h>
31#include <fcntl.h>
32#include <limits.h>
33#include <signal.h>
34#include <stdarg.h>
35#include <stdio.h>
36#include <stdlib.h>
37#include <string.h>
38#include <unistd.h>
39#include <limits.h>
40
41#include "atomicio.h"
42#include "log.h"
43#include "ssh-sandbox.h"
44#include "xmalloc.h"
45
46struct sandbox_policy {
47	int syscall;
48	int action;
49};
50
51/* Permitted syscalls in preauth. Unlisted syscalls get SYSTR_POLICY_KILL */
52static const struct sandbox_policy preauth_policy[] = {
53	{ SYS_open, SYSTR_POLICY_NEVER },
54
55#ifdef SYS_getentropy
56	/* OpenBSD 5.6 and newer use getentropy(2) to seed arc4random(3). */
57	{ SYS_getentropy, SYSTR_POLICY_PERMIT },
58#else
59	/* Previous releases used sysctl(3)'s kern.arnd variable. */
60	{ SYS___sysctl, SYSTR_POLICY_PERMIT },
61#endif
62
63#ifdef SYS_sendsyslog
64 	{ SYS_sendsyslog, SYSTR_POLICY_PERMIT },
65#endif
66	{ SYS_close, SYSTR_POLICY_PERMIT },
67	{ SYS_exit, SYSTR_POLICY_PERMIT },
68	{ SYS_getpid, SYSTR_POLICY_PERMIT },
69	{ SYS_gettimeofday, SYSTR_POLICY_PERMIT },
70	{ SYS_clock_gettime, SYSTR_POLICY_PERMIT },
71	{ SYS_madvise, SYSTR_POLICY_PERMIT },
72	{ SYS_mmap, SYSTR_POLICY_PERMIT },
73	{ SYS_mprotect, SYSTR_POLICY_PERMIT },
74	{ SYS_mquery, SYSTR_POLICY_PERMIT },
75	{ SYS_poll, SYSTR_POLICY_PERMIT },
76	{ SYS_munmap, SYSTR_POLICY_PERMIT },
77	{ SYS_read, SYSTR_POLICY_PERMIT },
78	{ SYS_select, SYSTR_POLICY_PERMIT },
79	{ SYS_shutdown, SYSTR_POLICY_PERMIT },
80	{ SYS_sigprocmask, SYSTR_POLICY_PERMIT },
81	{ SYS_write, SYSTR_POLICY_PERMIT },
82	{ -1, -1 }
83};
84
85struct ssh_sandbox {
86	int systrace_fd;
87	pid_t child_pid;
88	void (*osigchld)(int);
89};
90
91struct ssh_sandbox *
92ssh_sandbox_init(struct monitor *monitor)
93{
94	struct ssh_sandbox *box;
95
96	debug3("%s: preparing systrace sandbox", __func__);
97	box = xcalloc(1, sizeof(*box));
98	box->systrace_fd = -1;
99	box->child_pid = 0;
100	box->osigchld = signal(SIGCHLD, SIG_IGN);
101
102	return box;
103}
104
105void
106ssh_sandbox_child(struct ssh_sandbox *box)
107{
108	debug3("%s: ready", __func__);
109	signal(SIGCHLD, box->osigchld);
110	if (kill(getpid(), SIGSTOP) != 0)
111		fatal("%s: kill(%d, SIGSTOP)", __func__, getpid());
112	debug3("%s: started", __func__);
113}
114
115static void
116ssh_sandbox_parent(struct ssh_sandbox *box, pid_t child_pid,
117    const struct sandbox_policy *allowed_syscalls)
118{
119	int dev_systrace, i, j, found, status;
120	pid_t pid;
121	struct systrace_policy policy;
122
123	/* Wait for the child to send itself a SIGSTOP */
124	debug3("%s: wait for child %ld", __func__, (long)child_pid);
125	do {
126		pid = waitpid(child_pid, &status, WUNTRACED);
127	} while (pid == -1 && errno == EINTR);
128	signal(SIGCHLD, box->osigchld);
129	if (!WIFSTOPPED(status)) {
130		if (WIFSIGNALED(status))
131			fatal("%s: child terminated with signal %d",
132			    __func__, WTERMSIG(status));
133		if (WIFEXITED(status))
134			fatal("%s: child exited with status %d",
135			    __func__, WEXITSTATUS(status));
136		fatal("%s: child not stopped", __func__);
137	}
138	debug3("%s: child %ld stopped", __func__, (long)child_pid);
139	box->child_pid = child_pid;
140
141	/* Set up systracing of child */
142	if ((dev_systrace = open("/dev/systrace", O_RDONLY)) == -1)
143		fatal("%s: open(\"/dev/systrace\"): %s", __func__,
144		    strerror(errno));
145	if (ioctl(dev_systrace, STRIOCCLONE, &box->systrace_fd) == -1)
146		fatal("%s: ioctl(STRIOCCLONE, %d): %s", __func__,
147		    dev_systrace, strerror(errno));
148	close(dev_systrace);
149	debug3("%s: systrace attach, fd=%d", __func__, box->systrace_fd);
150	if (ioctl(box->systrace_fd, STRIOCATTACH, &child_pid) == -1)
151		fatal("%s: ioctl(%d, STRIOCATTACH, %d): %s", __func__,
152		    box->systrace_fd, child_pid, strerror(errno));
153
154	/* Allocate and assign policy */
155	memset(&policy, 0, sizeof(policy));
156	policy.strp_op = SYSTR_POLICY_NEW;
157	policy.strp_maxents = SYS_MAXSYSCALL;
158	if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1)
159		fatal("%s: ioctl(%d, STRIOCPOLICY (new)): %s", __func__,
160		    box->systrace_fd, strerror(errno));
161
162	policy.strp_op = SYSTR_POLICY_ASSIGN;
163	policy.strp_pid = box->child_pid;
164	if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1)
165		fatal("%s: ioctl(%d, STRIOCPOLICY (assign)): %s",
166		    __func__, box->systrace_fd, strerror(errno));
167
168	/* Set per-syscall policy */
169	for (i = 0; i < SYS_MAXSYSCALL; i++) {
170		found = 0;
171		for (j = 0; allowed_syscalls[j].syscall != -1; j++) {
172			if (allowed_syscalls[j].syscall == i) {
173				found = 1;
174				break;
175			}
176		}
177		policy.strp_op = SYSTR_POLICY_MODIFY;
178		policy.strp_code = i;
179		policy.strp_policy = found ?
180		    allowed_syscalls[j].action : SYSTR_POLICY_KILL;
181		if (found)
182			debug3("%s: policy: enable syscall %d", __func__, i);
183		if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1)
184			fatal("%s: ioctl(%d, STRIOCPOLICY (modify)): %s",
185			    __func__, box->systrace_fd, strerror(errno));
186	}
187
188	/* Signal the child to start running */
189	debug3("%s: start child %ld", __func__, (long)child_pid);
190	if (kill(box->child_pid, SIGCONT) != 0)
191		fatal("%s: kill(%d, SIGCONT)", __func__, box->child_pid);
192}
193
194void
195ssh_sandbox_parent_finish(struct ssh_sandbox *box)
196{
197	/* Closing this before the child exits will terminate it */
198	close(box->systrace_fd);
199
200	free(box);
201	debug3("%s: finished", __func__);
202}
203
204void
205ssh_sandbox_parent_preauth(struct ssh_sandbox *box, pid_t child_pid)
206{
207	ssh_sandbox_parent(box, child_pid, preauth_policy);
208}
209
210#endif /* SANDBOX_SYSTRACE */
211