xref: /openssh-portable/sandbox-systrace.c (revision 1c5b4bc8)
1 /* $OpenBSD: sandbox-systrace.c,v 1.18 2015/10/02 01:39:26 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 
46 struct sandbox_policy {
47 	int syscall;
48 	int action;
49 };
50 
51 /* Permitted syscalls in preauth. Unlisted syscalls get SYSTR_POLICY_KILL */
52 static const struct sandbox_policy preauth_policy[] = {
53 	{ SYS_exit, SYSTR_POLICY_PERMIT },
54 #ifdef SYS_kbind
55 	{ SYS_kbind, SYSTR_POLICY_PERMIT },
56 #endif
57 
58 	{ SYS_getpid, SYSTR_POLICY_PERMIT },
59 	{ SYS_getpgid, SYSTR_POLICY_PERMIT },
60 	{ SYS_clock_gettime, SYSTR_POLICY_PERMIT },
61 	{ SYS_gettimeofday, SYSTR_POLICY_PERMIT },
62 	{ SYS_nanosleep, SYSTR_POLICY_PERMIT },
63 	{ SYS_sigprocmask, SYSTR_POLICY_PERMIT },
64 
65 #ifdef SYS_getentropy
66 	/* OpenBSD 5.6 and newer use getentropy(2) to seed arc4random(3). */
67 	{ SYS_getentropy, SYSTR_POLICY_PERMIT },
68 #else
69 	/* Previous releases used sysctl(3)'s kern.arnd variable. */
70 	{ SYS___sysctl, SYSTR_POLICY_PERMIT },
71 #endif
72 #ifdef SYS_sendsyslog
73 	{ SYS_sendsyslog, SYSTR_POLICY_PERMIT },
74 #endif
75 
76 	{ SYS_madvise, SYSTR_POLICY_PERMIT },
77 	{ SYS_mmap, SYSTR_POLICY_PERMIT },
78 	{ SYS_mprotect, SYSTR_POLICY_PERMIT },
79 	{ SYS_mquery, SYSTR_POLICY_PERMIT },
80 	{ SYS_munmap, SYSTR_POLICY_PERMIT },
81 
82 	{ SYS_poll, SYSTR_POLICY_PERMIT },
83 	{ SYS_select, SYSTR_POLICY_PERMIT },
84 	{ SYS_read, SYSTR_POLICY_PERMIT },
85 	{ SYS_write, SYSTR_POLICY_PERMIT },
86 	{ SYS_shutdown, SYSTR_POLICY_PERMIT },
87 	{ SYS_close, SYSTR_POLICY_PERMIT },
88 
89 	{ SYS_open, SYSTR_POLICY_NEVER },
90 
91 	{ -1, -1 }
92 };
93 
94 struct ssh_sandbox {
95 	int systrace_fd;
96 	pid_t child_pid;
97 	void (*osigchld)(int);
98 };
99 
100 struct ssh_sandbox *
101 ssh_sandbox_init(struct monitor *monitor)
102 {
103 	struct ssh_sandbox *box;
104 
105 	debug3("%s: preparing systrace sandbox", __func__);
106 	box = xcalloc(1, sizeof(*box));
107 	box->systrace_fd = -1;
108 	box->child_pid = 0;
109 	box->osigchld = signal(SIGCHLD, SIG_IGN);
110 
111 	return box;
112 }
113 
114 void
115 ssh_sandbox_child(struct ssh_sandbox *box)
116 {
117 	debug3("%s: ready", __func__);
118 	signal(SIGCHLD, box->osigchld);
119 	if (kill(getpid(), SIGSTOP) != 0)
120 		fatal("%s: kill(%d, SIGSTOP)", __func__, getpid());
121 	debug3("%s: started", __func__);
122 }
123 
124 static void
125 ssh_sandbox_parent(struct ssh_sandbox *box, pid_t child_pid,
126     const struct sandbox_policy *allowed_syscalls)
127 {
128 	int dev_systrace, i, j, found, status;
129 	pid_t pid;
130 	struct systrace_policy policy;
131 
132 	/* Wait for the child to send itself a SIGSTOP */
133 	debug3("%s: wait for child %ld", __func__, (long)child_pid);
134 	do {
135 		pid = waitpid(child_pid, &status, WUNTRACED);
136 	} while (pid == -1 && errno == EINTR);
137 	signal(SIGCHLD, box->osigchld);
138 	if (!WIFSTOPPED(status)) {
139 		if (WIFSIGNALED(status))
140 			fatal("%s: child terminated with signal %d",
141 			    __func__, WTERMSIG(status));
142 		if (WIFEXITED(status))
143 			fatal("%s: child exited with status %d",
144 			    __func__, WEXITSTATUS(status));
145 		fatal("%s: child not stopped", __func__);
146 	}
147 	debug3("%s: child %ld stopped", __func__, (long)child_pid);
148 	box->child_pid = child_pid;
149 
150 	/* Set up systracing of child */
151 	if ((dev_systrace = open("/dev/systrace", O_RDONLY)) == -1)
152 		fatal("%s: open(\"/dev/systrace\"): %s", __func__,
153 		    strerror(errno));
154 	if (ioctl(dev_systrace, STRIOCCLONE, &box->systrace_fd) == -1)
155 		fatal("%s: ioctl(STRIOCCLONE, %d): %s", __func__,
156 		    dev_systrace, strerror(errno));
157 	close(dev_systrace);
158 	debug3("%s: systrace attach, fd=%d", __func__, box->systrace_fd);
159 	if (ioctl(box->systrace_fd, STRIOCATTACH, &child_pid) == -1)
160 		fatal("%s: ioctl(%d, STRIOCATTACH, %d): %s", __func__,
161 		    box->systrace_fd, child_pid, strerror(errno));
162 
163 	/* Allocate and assign policy */
164 	memset(&policy, 0, sizeof(policy));
165 	policy.strp_op = SYSTR_POLICY_NEW;
166 	policy.strp_maxents = SYS_MAXSYSCALL;
167 	if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1)
168 		fatal("%s: ioctl(%d, STRIOCPOLICY (new)): %s", __func__,
169 		    box->systrace_fd, strerror(errno));
170 
171 	policy.strp_op = SYSTR_POLICY_ASSIGN;
172 	policy.strp_pid = box->child_pid;
173 	if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1)
174 		fatal("%s: ioctl(%d, STRIOCPOLICY (assign)): %s",
175 		    __func__, box->systrace_fd, strerror(errno));
176 
177 	/* Set per-syscall policy */
178 	for (i = 0; i < SYS_MAXSYSCALL; i++) {
179 		found = 0;
180 		for (j = 0; allowed_syscalls[j].syscall != -1; j++) {
181 			if (allowed_syscalls[j].syscall == i) {
182 				found = 1;
183 				break;
184 			}
185 		}
186 		policy.strp_op = SYSTR_POLICY_MODIFY;
187 		policy.strp_code = i;
188 		policy.strp_policy = found ?
189 		    allowed_syscalls[j].action : SYSTR_POLICY_KILL;
190 		if (found)
191 			debug3("%s: policy: enable syscall %d", __func__, i);
192 		if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1)
193 			fatal("%s: ioctl(%d, STRIOCPOLICY (modify)): %s",
194 			    __func__, box->systrace_fd, strerror(errno));
195 	}
196 
197 	/* Signal the child to start running */
198 	debug3("%s: start child %ld", __func__, (long)child_pid);
199 	if (kill(box->child_pid, SIGCONT) != 0)
200 		fatal("%s: kill(%d, SIGCONT)", __func__, box->child_pid);
201 }
202 
203 void
204 ssh_sandbox_parent_finish(struct ssh_sandbox *box)
205 {
206 	/* Closing this before the child exits will terminate it */
207 	close(box->systrace_fd);
208 
209 	free(box);
210 	debug3("%s: finished", __func__);
211 }
212 
213 void
214 ssh_sandbox_parent_preauth(struct ssh_sandbox *box, pid_t child_pid)
215 {
216 	ssh_sandbox_parent(box, child_pid, preauth_policy);
217 }
218 
219 #endif /* SANDBOX_SYSTRACE */
220