1/* $OpenBSD: sandbox-systrace.c,v 1.6 2012/06/30 14:35:09 markus 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/param.h>
24#include <sys/ioctl.h>
25#include <sys/syscall.h>
26#include <sys/socket.h>
27#include <sys/wait.h>
28
29#include <dev/systrace.h>
30
31#include <errno.h>
32#include <fcntl.h>
33#include <limits.h>
34#include <signal.h>
35#include <stdarg.h>
36#include <stdio.h>
37#include <stdlib.h>
38#include <string.h>
39#include <unistd.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	{ SYS___sysctl, SYSTR_POLICY_PERMIT },
56	{ SYS_close, SYSTR_POLICY_PERMIT },
57	{ SYS_exit, SYSTR_POLICY_PERMIT },
58	{ SYS_getpid, SYSTR_POLICY_PERMIT },
59	{ SYS_gettimeofday, SYSTR_POLICY_PERMIT },
60	{ SYS_madvise, SYSTR_POLICY_PERMIT },
61	{ SYS_mmap, SYSTR_POLICY_PERMIT },
62	{ SYS_mprotect, SYSTR_POLICY_PERMIT },
63	{ SYS_mquery, SYSTR_POLICY_PERMIT },
64	{ SYS_poll, SYSTR_POLICY_PERMIT },
65	{ SYS_munmap, SYSTR_POLICY_PERMIT },
66	{ SYS_read, SYSTR_POLICY_PERMIT },
67	{ SYS_select, SYSTR_POLICY_PERMIT },
68	{ SYS_sigprocmask, SYSTR_POLICY_PERMIT },
69	{ SYS_write, SYSTR_POLICY_PERMIT },
70	{ -1, -1 }
71};
72
73struct ssh_sandbox {
74	int systrace_fd;
75	pid_t child_pid;
76	void (*osigchld)(int);
77};
78
79struct ssh_sandbox *
80ssh_sandbox_init(void)
81{
82	struct ssh_sandbox *box;
83
84	debug3("%s: preparing systrace sandbox", __func__);
85	box = xcalloc(1, sizeof(*box));
86	box->systrace_fd = -1;
87	box->child_pid = 0;
88	box->osigchld = signal(SIGCHLD, SIG_IGN);
89
90	return box;
91}
92
93void
94ssh_sandbox_child(struct ssh_sandbox *box)
95{
96	debug3("%s: ready", __func__);
97	signal(SIGCHLD, box->osigchld);
98	if (kill(getpid(), SIGSTOP) != 0)
99		fatal("%s: kill(%d, SIGSTOP)", __func__, getpid());
100	debug3("%s: started", __func__);
101}
102
103static void
104ssh_sandbox_parent(struct ssh_sandbox *box, pid_t child_pid,
105    const struct sandbox_policy *allowed_syscalls)
106{
107	int dev_systrace, i, j, found, status;
108	pid_t pid;
109	struct systrace_policy policy;
110
111	/* Wait for the child to send itself a SIGSTOP */
112	debug3("%s: wait for child %ld", __func__, (long)child_pid);
113	do {
114		pid = waitpid(child_pid, &status, WUNTRACED);
115	} while (pid == -1 && errno == EINTR);
116	signal(SIGCHLD, box->osigchld);
117	if (!WIFSTOPPED(status)) {
118		if (WIFSIGNALED(status))
119			fatal("%s: child terminated with signal %d",
120			    __func__, WTERMSIG(status));
121		if (WIFEXITED(status))
122			fatal("%s: child exited with status %d",
123			    __func__, WEXITSTATUS(status));
124		fatal("%s: child not stopped", __func__);
125	}
126	debug3("%s: child %ld stopped", __func__, (long)child_pid);
127	box->child_pid = child_pid;
128
129	/* Set up systracing of child */
130	if ((dev_systrace = open("/dev/systrace", O_RDONLY)) == -1)
131		fatal("%s: open(\"/dev/systrace\"): %s", __func__,
132		    strerror(errno));
133	if (ioctl(dev_systrace, STRIOCCLONE, &box->systrace_fd) == -1)
134		fatal("%s: ioctl(STRIOCCLONE, %d): %s", __func__,
135		    dev_systrace, strerror(errno));
136	close(dev_systrace);
137	debug3("%s: systrace attach, fd=%d", __func__, box->systrace_fd);
138	if (ioctl(box->systrace_fd, STRIOCATTACH, &child_pid) == -1)
139		fatal("%s: ioctl(%d, STRIOCATTACH, %d): %s", __func__,
140		    box->systrace_fd, child_pid, strerror(errno));
141
142	/* Allocate and assign policy */
143	bzero(&policy, sizeof(policy));
144	policy.strp_op = SYSTR_POLICY_NEW;
145	policy.strp_maxents = SYS_MAXSYSCALL;
146	if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1)
147		fatal("%s: ioctl(%d, STRIOCPOLICY (new)): %s", __func__,
148		    box->systrace_fd, strerror(errno));
149
150	policy.strp_op = SYSTR_POLICY_ASSIGN;
151	policy.strp_pid = box->child_pid;
152	if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1)
153		fatal("%s: ioctl(%d, STRIOCPOLICY (assign)): %s",
154		    __func__, box->systrace_fd, strerror(errno));
155
156	/* Set per-syscall policy */
157	for (i = 0; i < SYS_MAXSYSCALL; i++) {
158		found = 0;
159		for (j = 0; allowed_syscalls[j].syscall != -1; j++) {
160			if (allowed_syscalls[j].syscall == i) {
161				found = 1;
162				break;
163			}
164		}
165		policy.strp_op = SYSTR_POLICY_MODIFY;
166		policy.strp_code = i;
167		policy.strp_policy = found ?
168		    allowed_syscalls[j].action : SYSTR_POLICY_KILL;
169		if (found)
170			debug3("%s: policy: enable syscall %d", __func__, i);
171		if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1)
172			fatal("%s: ioctl(%d, STRIOCPOLICY (modify)): %s",
173			    __func__, box->systrace_fd, strerror(errno));
174	}
175
176	/* Signal the child to start running */
177	debug3("%s: start child %ld", __func__, (long)child_pid);
178	if (kill(box->child_pid, SIGCONT) != 0)
179		fatal("%s: kill(%d, SIGCONT)", __func__, box->child_pid);
180}
181
182void
183ssh_sandbox_parent_finish(struct ssh_sandbox *box)
184{
185	/* Closing this before the child exits will terminate it */
186	close(box->systrace_fd);
187
188	free(box);
189	debug3("%s: finished", __func__);
190}
191
192void
193ssh_sandbox_parent_preauth(struct ssh_sandbox *box, pid_t child_pid)
194{
195	ssh_sandbox_parent(box, child_pid, preauth_policy);
196}
197
198#endif /* SANDBOX_SYSTRACE */
199