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Darren Tuckerb759c9c2013-06-02 07:46:16 +10001/* $OpenBSD: sandbox-systrace.c,v 1.7 2013/06/01 13:15:52 dtucker 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
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>
Darren Tucker3b4b2d32012-07-02 18:54:31 +100027#include <sys/wait.h>
Damien Miller69ff1df2011-06-23 08:30:03 +100028
29#include <dev/systrace.h>
30
31#include <errno.h>
32#include <fcntl.h>
33#include <limits.h>
Darren Tucker3b4b2d32012-07-02 18:54:31 +100034#include <signal.h>
Damien Miller69ff1df2011-06-23 08:30:03 +100035#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"
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[] = {
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 },
Darren Tuckerb759c9c2013-06-02 07:46:16 +100060 { SYS_clock_gettime, SYSTR_POLICY_PERMIT },
Damien Miller35e48192011-08-06 06:16:23 +100061 { SYS_madvise, SYSTR_POLICY_PERMIT },
62 { SYS_mmap, SYSTR_POLICY_PERMIT },
63 { SYS_mprotect, SYSTR_POLICY_PERMIT },
Damien Miller560de922012-06-30 08:33:53 +100064 { SYS_mquery, SYSTR_POLICY_PERMIT },
Damien Miller35e48192011-08-06 06:16:23 +100065 { SYS_poll, SYSTR_POLICY_PERMIT },
66 { SYS_munmap, SYSTR_POLICY_PERMIT },
67 { SYS_read, SYSTR_POLICY_PERMIT },
68 { SYS_select, SYSTR_POLICY_PERMIT },
69 { SYS_sigprocmask, SYSTR_POLICY_PERMIT },
70 { SYS_write, SYSTR_POLICY_PERMIT },
71 { -1, -1 }
Damien Miller69ff1df2011-06-23 08:30:03 +100072};
73
74struct ssh_sandbox {
Damien Miller69ff1df2011-06-23 08:30:03 +100075 int systrace_fd;
76 pid_t child_pid;
Darren Tucker3b4b2d32012-07-02 18:54:31 +100077 void (*osigchld)(int);
Damien Miller69ff1df2011-06-23 08:30:03 +100078};
79
80struct ssh_sandbox *
81ssh_sandbox_init(void)
82{
83 struct ssh_sandbox *box;
Damien Miller69ff1df2011-06-23 08:30:03 +100084
85 debug3("%s: preparing systrace sandbox", __func__);
86 box = xcalloc(1, sizeof(*box));
Damien Miller69ff1df2011-06-23 08:30:03 +100087 box->systrace_fd = -1;
88 box->child_pid = 0;
Darren Tucker3b4b2d32012-07-02 18:54:31 +100089 box->osigchld = signal(SIGCHLD, SIG_IGN);
Damien Miller69ff1df2011-06-23 08:30:03 +100090
91 return box;
92}
93
94void
95ssh_sandbox_child(struct ssh_sandbox *box)
96{
Damien Miller69ff1df2011-06-23 08:30:03 +100097 debug3("%s: ready", __func__);
Darren Tucker3b4b2d32012-07-02 18:54:31 +100098 signal(SIGCHLD, box->osigchld);
99 if (kill(getpid(), SIGSTOP) != 0)
100 fatal("%s: kill(%d, SIGSTOP)", __func__, getpid());
Damien Miller69ff1df2011-06-23 08:30:03 +1000101 debug3("%s: started", __func__);
Damien Miller69ff1df2011-06-23 08:30:03 +1000102}
103
104static void
105ssh_sandbox_parent(struct ssh_sandbox *box, pid_t child_pid,
Damien Miller35e48192011-08-06 06:16:23 +1000106 const struct sandbox_policy *allowed_syscalls)
Damien Miller69ff1df2011-06-23 08:30:03 +1000107{
Darren Tucker3b4b2d32012-07-02 18:54:31 +1000108 int dev_systrace, i, j, found, status;
109 pid_t pid;
Damien Miller35e48192011-08-06 06:16:23 +1000110 struct systrace_policy policy;
Damien Miller69ff1df2011-06-23 08:30:03 +1000111
Darren Tucker3b4b2d32012-07-02 18:54:31 +1000112 /* Wait for the child to send itself a SIGSTOP */
Damien Miller69ff1df2011-06-23 08:30:03 +1000113 debug3("%s: wait for child %ld", __func__, (long)child_pid);
Darren Tucker3b4b2d32012-07-02 18:54:31 +1000114 do {
115 pid = waitpid(child_pid, &status, WUNTRACED);
116 } while (pid == -1 && errno == EINTR);
117 signal(SIGCHLD, box->osigchld);
118 if (!WIFSTOPPED(status)) {
119 if (WIFSIGNALED(status))
120 fatal("%s: child terminated with signal %d",
121 __func__, WTERMSIG(status));
122 if (WIFEXITED(status))
123 fatal("%s: child exited with status %d",
124 __func__, WEXITSTATUS(status));
125 fatal("%s: child not stopped", __func__);
126 }
127 debug3("%s: child %ld stopped", __func__, (long)child_pid);
Damien Miller69ff1df2011-06-23 08:30:03 +1000128 box->child_pid = child_pid;
Damien Miller69ff1df2011-06-23 08:30:03 +1000129
130 /* Set up systracing of child */
131 if ((dev_systrace = open("/dev/systrace", O_RDONLY)) == -1)
132 fatal("%s: open(\"/dev/systrace\"): %s", __func__,
133 strerror(errno));
134 if (ioctl(dev_systrace, STRIOCCLONE, &box->systrace_fd) == -1)
135 fatal("%s: ioctl(STRIOCCLONE, %d): %s", __func__,
136 dev_systrace, strerror(errno));
137 close(dev_systrace);
138 debug3("%s: systrace attach, fd=%d", __func__, box->systrace_fd);
139 if (ioctl(box->systrace_fd, STRIOCATTACH, &child_pid) == -1)
140 fatal("%s: ioctl(%d, STRIOCATTACH, %d): %s", __func__,
141 box->systrace_fd, child_pid, strerror(errno));
142
143 /* Allocate and assign policy */
Damien Miller35e48192011-08-06 06:16:23 +1000144 bzero(&policy, sizeof(policy));
145 policy.strp_op = SYSTR_POLICY_NEW;
146 policy.strp_maxents = SYS_MAXSYSCALL;
147 if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1)
Damien Miller69ff1df2011-06-23 08:30:03 +1000148 fatal("%s: ioctl(%d, STRIOCPOLICY (new)): %s", __func__,
149 box->systrace_fd, strerror(errno));
150
Damien Miller35e48192011-08-06 06:16:23 +1000151 policy.strp_op = SYSTR_POLICY_ASSIGN;
152 policy.strp_pid = box->child_pid;
153 if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1)
Damien Miller69ff1df2011-06-23 08:30:03 +1000154 fatal("%s: ioctl(%d, STRIOCPOLICY (assign)): %s",
155 __func__, box->systrace_fd, strerror(errno));
156
157 /* Set per-syscall policy */
158 for (i = 0; i < SYS_MAXSYSCALL; i++) {
Damien Miller35e48192011-08-06 06:16:23 +1000159 found = 0;
160 for (j = 0; allowed_syscalls[j].syscall != -1; j++) {
161 if (allowed_syscalls[j].syscall == i) {
Damien Miller69ff1df2011-06-23 08:30:03 +1000162 found = 1;
Damien Miller35e48192011-08-06 06:16:23 +1000163 break;
164 }
Damien Miller69ff1df2011-06-23 08:30:03 +1000165 }
Damien Miller35e48192011-08-06 06:16:23 +1000166 policy.strp_op = SYSTR_POLICY_MODIFY;
167 policy.strp_code = i;
168 policy.strp_policy = found ?
169 allowed_syscalls[j].action : SYSTR_POLICY_KILL;
Damien Miller69ff1df2011-06-23 08:30:03 +1000170 if (found)
171 debug3("%s: policy: enable syscall %d", __func__, i);
Damien Miller35e48192011-08-06 06:16:23 +1000172 if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1)
Damien Miller69ff1df2011-06-23 08:30:03 +1000173 fatal("%s: ioctl(%d, STRIOCPOLICY (modify)): %s",
174 __func__, box->systrace_fd, strerror(errno));
175 }
176
177 /* Signal the child to start running */
178 debug3("%s: start child %ld", __func__, (long)child_pid);
Darren Tucker3b4b2d32012-07-02 18:54:31 +1000179 if (kill(box->child_pid, SIGCONT) != 0)
180 fatal("%s: kill(%d, SIGCONT)", __func__, box->child_pid);
Damien Miller69ff1df2011-06-23 08:30:03 +1000181}
182
183void
184ssh_sandbox_parent_finish(struct ssh_sandbox *box)
185{
186 /* Closing this before the child exits will terminate it */
187 close(box->systrace_fd);
188
189 free(box);
190 debug3("%s: finished", __func__);
191}
192
193void
194ssh_sandbox_parent_preauth(struct ssh_sandbox *box, pid_t child_pid)
195{
196 ssh_sandbox_parent(box, child_pid, preauth_policy);
197}
198
199#endif /* SANDBOX_SYSTRACE */