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deraadt@openbsd.orgc61b42f2015-10-02 01:39:26 +00001/* $OpenBSD: sandbox-systrace.c,v 1.18 2015/10/02 01:39:26 deraadt Exp $ */
Damien Miller69ff1df2011-06-23 08:30:03 +10002/*
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
Damien Miller0dc74512015-10-05 18:33:05 -070018#include "includes.h"
19
20#ifdef SANDBOX_SYSTRACE
21
Damien Miller69ff1df2011-06-23 08:30:03 +100022#include <sys/types.h>
Damien Miller69ff1df2011-06-23 08:30:03 +100023#include <sys/ioctl.h>
24#include <sys/syscall.h>
25#include <sys/socket.h>
Darren Tucker3b4b2d32012-07-02 18:54:31 +100026#include <sys/wait.h>
Damien Miller69ff1df2011-06-23 08:30:03 +100027
28#include <dev/systrace.h>
29
30#include <errno.h>
31#include <fcntl.h>
32#include <limits.h>
Darren Tucker3b4b2d32012-07-02 18:54:31 +100033#include <signal.h>
Damien Miller69ff1df2011-06-23 08:30:03 +100034#include <stdarg.h>
35#include <stdio.h>
36#include <stdlib.h>
37#include <string.h>
38#include <unistd.h>
deraadt@openbsd.org087266e2015-01-20 23:14:00 +000039#include <limits.h>
Damien Miller69ff1df2011-06-23 08:30:03 +100040
41#include "atomicio.h"
42#include "log.h"
Damien Millerdcbd41e2011-06-23 19:45:51 +100043#include "ssh-sandbox.h"
Damien Miller69ff1df2011-06-23 08:30:03 +100044#include "xmalloc.h"
45
Damien Miller35e48192011-08-06 06:16:23 +100046struct 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[] = {
deraadt@openbsd.org7cc44ef2015-05-18 15:06:05 +000053 { SYS_exit, SYSTR_POLICY_PERMIT },
deraadt@openbsd.orgc61b42f2015-10-02 01:39:26 +000054#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_sigprocmask, SYSTR_POLICY_PERMIT },
63
Damien Miller84a89162014-07-02 12:47:48 +100064#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. */
Damien Miller35e48192011-08-06 06:16:23 +100069 { SYS___sysctl, SYSTR_POLICY_PERMIT },
Damien Miller84a89162014-07-02 12:47:48 +100070#endif
Darren Tucker996b24c2015-10-29 20:57:34 +110071#ifdef SYS_sendsyslog
deraadt@openbsd.orgc61b42f2015-10-02 01:39:26 +000072 { SYS_sendsyslog, SYSTR_POLICY_PERMIT },
Darren Tucker996b24c2015-10-29 20:57:34 +110073#endif
deraadt@openbsd.orgc61b42f2015-10-02 01:39:26 +000074
Damien Miller35e48192011-08-06 06:16:23 +100075 { SYS_madvise, SYSTR_POLICY_PERMIT },
76 { SYS_mmap, SYSTR_POLICY_PERMIT },
77 { SYS_mprotect, SYSTR_POLICY_PERMIT },
Damien Miller560de922012-06-30 08:33:53 +100078 { SYS_mquery, SYSTR_POLICY_PERMIT },
Damien Miller35e48192011-08-06 06:16:23 +100079 { SYS_munmap, SYSTR_POLICY_PERMIT },
deraadt@openbsd.orgc61b42f2015-10-02 01:39:26 +000080
deraadt@openbsd.org7cc44ef2015-05-18 15:06:05 +000081 { SYS_poll, SYSTR_POLICY_PERMIT },
Damien Miller35e48192011-08-06 06:16:23 +100082 { SYS_select, SYSTR_POLICY_PERMIT },
deraadt@openbsd.orgc61b42f2015-10-02 01:39:26 +000083 { SYS_read, SYSTR_POLICY_PERMIT },
Damien Miller35e48192011-08-06 06:16:23 +100084 { SYS_write, SYSTR_POLICY_PERMIT },
deraadt@openbsd.orgc61b42f2015-10-02 01:39:26 +000085 { SYS_shutdown, SYSTR_POLICY_PERMIT },
86 { SYS_close, SYSTR_POLICY_PERMIT },
87
88 { SYS_open, SYSTR_POLICY_NEVER },
89
Damien Miller35e48192011-08-06 06:16:23 +100090 { -1, -1 }
Damien Miller69ff1df2011-06-23 08:30:03 +100091};
92
93struct ssh_sandbox {
Damien Miller69ff1df2011-06-23 08:30:03 +100094 int systrace_fd;
95 pid_t child_pid;
Darren Tucker3b4b2d32012-07-02 18:54:31 +100096 void (*osigchld)(int);
Damien Miller69ff1df2011-06-23 08:30:03 +100097};
98
99struct ssh_sandbox *
Damien Miller0dc74512015-10-05 18:33:05 -0700100ssh_sandbox_init(struct monitor *monitor)
Damien Miller69ff1df2011-06-23 08:30:03 +1000101{
102 struct ssh_sandbox *box;
Damien Miller69ff1df2011-06-23 08:30:03 +1000103
104 debug3("%s: preparing systrace sandbox", __func__);
105 box = xcalloc(1, sizeof(*box));
Damien Miller69ff1df2011-06-23 08:30:03 +1000106 box->systrace_fd = -1;
107 box->child_pid = 0;
Darren Tucker3b4b2d32012-07-02 18:54:31 +1000108 box->osigchld = signal(SIGCHLD, SIG_IGN);
Damien Miller69ff1df2011-06-23 08:30:03 +1000109
110 return box;
111}
112
113void
114ssh_sandbox_child(struct ssh_sandbox *box)
115{
Damien Miller69ff1df2011-06-23 08:30:03 +1000116 debug3("%s: ready", __func__);
Darren Tucker3b4b2d32012-07-02 18:54:31 +1000117 signal(SIGCHLD, box->osigchld);
118 if (kill(getpid(), SIGSTOP) != 0)
119 fatal("%s: kill(%d, SIGSTOP)", __func__, getpid());
Damien Miller69ff1df2011-06-23 08:30:03 +1000120 debug3("%s: started", __func__);
Damien Miller69ff1df2011-06-23 08:30:03 +1000121}
122
123static void
124ssh_sandbox_parent(struct ssh_sandbox *box, pid_t child_pid,
Damien Miller35e48192011-08-06 06:16:23 +1000125 const struct sandbox_policy *allowed_syscalls)
Damien Miller69ff1df2011-06-23 08:30:03 +1000126{
Darren Tucker3b4b2d32012-07-02 18:54:31 +1000127 int dev_systrace, i, j, found, status;
128 pid_t pid;
Damien Miller35e48192011-08-06 06:16:23 +1000129 struct systrace_policy policy;
Damien Miller69ff1df2011-06-23 08:30:03 +1000130
Darren Tucker3b4b2d32012-07-02 18:54:31 +1000131 /* Wait for the child to send itself a SIGSTOP */
Damien Miller69ff1df2011-06-23 08:30:03 +1000132 debug3("%s: wait for child %ld", __func__, (long)child_pid);
Darren Tucker3b4b2d32012-07-02 18:54:31 +1000133 do {
134 pid = waitpid(child_pid, &status, WUNTRACED);
135 } while (pid == -1 && errno == EINTR);
136 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);
Damien Miller69ff1df2011-06-23 08:30:03 +1000147 box->child_pid = child_pid;
Damien Miller69ff1df2011-06-23 08:30:03 +1000148
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 */
Damien Miller1d2c4562014-02-04 11:18:20 +1100163 memset(&policy, 0, sizeof(policy));
Damien Miller35e48192011-08-06 06:16:23 +1000164 policy.strp_op = SYSTR_POLICY_NEW;
165 policy.strp_maxents = SYS_MAXSYSCALL;
166 if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1)
Damien Miller69ff1df2011-06-23 08:30:03 +1000167 fatal("%s: ioctl(%d, STRIOCPOLICY (new)): %s", __func__,
168 box->systrace_fd, strerror(errno));
169
Damien Miller35e48192011-08-06 06:16:23 +1000170 policy.strp_op = SYSTR_POLICY_ASSIGN;
171 policy.strp_pid = box->child_pid;
172 if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1)
Damien Miller69ff1df2011-06-23 08:30:03 +1000173 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++) {
Damien Miller35e48192011-08-06 06:16:23 +1000178 found = 0;
179 for (j = 0; allowed_syscalls[j].syscall != -1; j++) {
180 if (allowed_syscalls[j].syscall == i) {
Damien Miller69ff1df2011-06-23 08:30:03 +1000181 found = 1;
Damien Miller35e48192011-08-06 06:16:23 +1000182 break;
183 }
Damien Miller69ff1df2011-06-23 08:30:03 +1000184 }
Damien Miller35e48192011-08-06 06:16:23 +1000185 policy.strp_op = SYSTR_POLICY_MODIFY;
186 policy.strp_code = i;
187 policy.strp_policy = found ?
188 allowed_syscalls[j].action : SYSTR_POLICY_KILL;
Damien Miller69ff1df2011-06-23 08:30:03 +1000189 if (found)
190 debug3("%s: policy: enable syscall %d", __func__, i);
Damien Miller35e48192011-08-06 06:16:23 +1000191 if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1)
Damien Miller69ff1df2011-06-23 08:30:03 +1000192 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);
Darren Tucker3b4b2d32012-07-02 18:54:31 +1000198 if (kill(box->child_pid, SIGCONT) != 0)
199 fatal("%s: kill(%d, SIGCONT)", __func__, box->child_pid);
Damien Miller69ff1df2011-06-23 08:30:03 +1000200}
201
202void
203ssh_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
212void
213ssh_sandbox_parent_preauth(struct ssh_sandbox *box, pid_t child_pid)
214{
215 ssh_sandbox_parent(box, child_pid, preauth_policy);
216}
Damien Miller0dc74512015-10-05 18:33:05 -0700217
218#endif /* SANDBOX_SYSTRACE */