xref: /openssh-portable/sandbox-systrace.c (revision 3bf2a6ac)
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 
40 #include "atomicio.h"
41 #include "log.h"
42 #include "ssh-sandbox.h"
43 #include "xmalloc.h"
44 
45 struct sandbox_policy {
46 	int syscall;
47 	int action;
48 };
49 
50 /* Permitted syscalls in preauth. Unlisted syscalls get SYSTR_POLICY_KILL */
51 static const struct sandbox_policy preauth_policy[] = {
52 	{ SYS_exit, SYSTR_POLICY_PERMIT },
53 #ifdef SYS_kbind
54 	{ SYS_kbind, SYSTR_POLICY_PERMIT },
55 #endif
56 
57 	{ SYS_getpid, SYSTR_POLICY_PERMIT },
58 	{ SYS_getpgid, SYSTR_POLICY_PERMIT },
59 	{ SYS_clock_gettime, SYSTR_POLICY_PERMIT },
60 	{ SYS_gettimeofday, SYSTR_POLICY_PERMIT },
61 	{ SYS_nanosleep, SYSTR_POLICY_PERMIT },
62 	{ SYS_sigprocmask, SYSTR_POLICY_PERMIT },
63 
64 #ifdef SYS_getentropy
65 	/* OpenBSD 5.6 and newer use getentropy(2) to seed arc4random(3). */
66 	{ SYS_getentropy, SYSTR_POLICY_PERMIT },
67 #else
68 	/* Previous releases used sysctl(3)'s kern.arnd variable. */
69 	{ SYS___sysctl, SYSTR_POLICY_PERMIT },
70 #endif
71 #ifdef SYS_sendsyslog
72 	{ SYS_sendsyslog, SYSTR_POLICY_PERMIT },
73 #endif
74 
75 	{ SYS_madvise, SYSTR_POLICY_PERMIT },
76 	{ SYS_mmap, SYSTR_POLICY_PERMIT },
77 	{ SYS_mprotect, SYSTR_POLICY_PERMIT },
78 	{ SYS_mquery, SYSTR_POLICY_PERMIT },
79 	{ SYS_munmap, SYSTR_POLICY_PERMIT },
80 
81 	{ SYS_poll, SYSTR_POLICY_PERMIT },
82 	{ SYS_select, SYSTR_POLICY_PERMIT },
83 	{ SYS_read, SYSTR_POLICY_PERMIT },
84 	{ SYS_write, SYSTR_POLICY_PERMIT },
85 	{ SYS_shutdown, SYSTR_POLICY_PERMIT },
86 	{ SYS_close, SYSTR_POLICY_PERMIT },
87 
88 	{ SYS_open, SYSTR_POLICY_NEVER },
89 
90 	{ -1, -1 }
91 };
92 
93 struct ssh_sandbox {
94 	int systrace_fd;
95 	pid_t child_pid;
96 	void (*osigchld)(int);
97 };
98 
99 struct ssh_sandbox *
ssh_sandbox_init(struct monitor * monitor)100 ssh_sandbox_init(struct monitor *monitor)
101 {
102 	struct ssh_sandbox *box;
103 
104 	debug3("%s: preparing systrace sandbox", __func__);
105 	box = xcalloc(1, sizeof(*box));
106 	box->systrace_fd = -1;
107 	box->child_pid = 0;
108 	box->osigchld = ssh_signal(SIGCHLD, SIG_IGN);
109 
110 	return box;
111 }
112 
113 void
ssh_sandbox_child(struct ssh_sandbox * box)114 ssh_sandbox_child(struct ssh_sandbox *box)
115 {
116 	debug3("%s: ready", __func__);
117 	ssh_signal(SIGCHLD, box->osigchld);
118 	if (kill(getpid(), SIGSTOP) != 0)
119 		fatal("%s: kill(%d, SIGSTOP)", __func__, getpid());
120 	debug3("%s: started", __func__);
121 }
122 
123 static void
ssh_sandbox_parent(struct ssh_sandbox * box,pid_t child_pid,const struct sandbox_policy * allowed_syscalls)124 ssh_sandbox_parent(struct ssh_sandbox *box, pid_t child_pid,
125     const struct sandbox_policy *allowed_syscalls)
126 {
127 	int dev_systrace, i, j, found, status;
128 	pid_t pid;
129 	struct systrace_policy policy;
130 
131 	/* Wait for the child to send itself a SIGSTOP */
132 	debug3("%s: wait for child %ld", __func__, (long)child_pid);
133 	do {
134 		pid = waitpid(child_pid, &status, WUNTRACED);
135 	} while (pid == -1 && errno == EINTR);
136 	ssh_signal(SIGCHLD, box->osigchld);
137 	if (!WIFSTOPPED(status)) {
138 		if (WIFSIGNALED(status))
139 			fatal("%s: child terminated with signal %d",
140 			    __func__, WTERMSIG(status));
141 		if (WIFEXITED(status))
142 			fatal("%s: child exited with status %d",
143 			    __func__, WEXITSTATUS(status));
144 		fatal("%s: child not stopped", __func__);
145 	}
146 	debug3("%s: child %ld stopped", __func__, (long)child_pid);
147 	box->child_pid = child_pid;
148 
149 	/* Set up systracing of child */
150 	if ((dev_systrace = open("/dev/systrace", O_RDONLY)) == -1)
151 		fatal("%s: open(\"/dev/systrace\"): %s", __func__,
152 		    strerror(errno));
153 	if (ioctl(dev_systrace, STRIOCCLONE, &box->systrace_fd) == -1)
154 		fatal("%s: ioctl(STRIOCCLONE, %d): %s", __func__,
155 		    dev_systrace, strerror(errno));
156 	close(dev_systrace);
157 	debug3("%s: systrace attach, fd=%d", __func__, box->systrace_fd);
158 	if (ioctl(box->systrace_fd, STRIOCATTACH, &child_pid) == -1)
159 		fatal("%s: ioctl(%d, STRIOCATTACH, %d): %s", __func__,
160 		    box->systrace_fd, child_pid, strerror(errno));
161 
162 	/* Allocate and assign policy */
163 	memset(&policy, 0, sizeof(policy));
164 	policy.strp_op = SYSTR_POLICY_NEW;
165 	policy.strp_maxents = SYS_MAXSYSCALL;
166 	if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1)
167 		fatal("%s: ioctl(%d, STRIOCPOLICY (new)): %s", __func__,
168 		    box->systrace_fd, strerror(errno));
169 
170 	policy.strp_op = SYSTR_POLICY_ASSIGN;
171 	policy.strp_pid = box->child_pid;
172 	if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1)
173 		fatal("%s: ioctl(%d, STRIOCPOLICY (assign)): %s",
174 		    __func__, box->systrace_fd, strerror(errno));
175 
176 	/* Set per-syscall policy */
177 	for (i = 0; i < SYS_MAXSYSCALL; i++) {
178 		found = 0;
179 		for (j = 0; allowed_syscalls[j].syscall != -1; j++) {
180 			if (allowed_syscalls[j].syscall == i) {
181 				found = 1;
182 				break;
183 			}
184 		}
185 		policy.strp_op = SYSTR_POLICY_MODIFY;
186 		policy.strp_code = i;
187 		policy.strp_policy = found ?
188 		    allowed_syscalls[j].action : SYSTR_POLICY_KILL;
189 		if (found)
190 			debug3("%s: policy: enable syscall %d", __func__, i);
191 		if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1)
192 			fatal("%s: ioctl(%d, STRIOCPOLICY (modify)): %s",
193 			    __func__, box->systrace_fd, strerror(errno));
194 	}
195 
196 	/* Signal the child to start running */
197 	debug3("%s: start child %ld", __func__, (long)child_pid);
198 	if (kill(box->child_pid, SIGCONT) != 0)
199 		fatal("%s: kill(%d, SIGCONT)", __func__, box->child_pid);
200 }
201 
202 void
ssh_sandbox_parent_finish(struct ssh_sandbox * box)203 ssh_sandbox_parent_finish(struct ssh_sandbox *box)
204 {
205 	/* Closing this before the child exits will terminate it */
206 	close(box->systrace_fd);
207 
208 	free(box);
209 	debug3("%s: finished", __func__);
210 }
211 
212 void
ssh_sandbox_parent_preauth(struct ssh_sandbox * box,pid_t child_pid)213 ssh_sandbox_parent_preauth(struct ssh_sandbox *box, pid_t child_pid)
214 {
215 	ssh_sandbox_parent(box, child_pid, preauth_policy);
216 }
217 
218 #endif /* SANDBOX_SYSTRACE */
219