1 /* $OpenBSD: sandbox-systrace.c,v 1.14 2015/01/20 23:14:00 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_open, SYSTR_POLICY_NEVER },
54
55 #ifdef SYS_getentropy
56 /* OpenBSD 5.6 and newer use getentropy(2) to seed arc4random(3). */
57 { SYS_getentropy, SYSTR_POLICY_PERMIT },
58 #else
59 /* Previous releases used sysctl(3)'s kern.arnd variable. */
60 { SYS___sysctl, SYSTR_POLICY_PERMIT },
61 #endif
62
63 #ifdef SYS_sendsyslog
64 { SYS_sendsyslog, SYSTR_POLICY_PERMIT },
65 #endif
66 { SYS_close, SYSTR_POLICY_PERMIT },
67 { SYS_exit, SYSTR_POLICY_PERMIT },
68 { SYS_getpid, SYSTR_POLICY_PERMIT },
69 { SYS_gettimeofday, SYSTR_POLICY_PERMIT },
70 { SYS_clock_gettime, SYSTR_POLICY_PERMIT },
71 { SYS_madvise, SYSTR_POLICY_PERMIT },
72 { SYS_mmap, SYSTR_POLICY_PERMIT },
73 { SYS_mprotect, SYSTR_POLICY_PERMIT },
74 { SYS_mquery, SYSTR_POLICY_PERMIT },
75 { SYS_poll, SYSTR_POLICY_PERMIT },
76 { SYS_munmap, SYSTR_POLICY_PERMIT },
77 { SYS_read, SYSTR_POLICY_PERMIT },
78 { SYS_select, SYSTR_POLICY_PERMIT },
79 { SYS_shutdown, SYSTR_POLICY_PERMIT },
80 { SYS_sigprocmask, SYSTR_POLICY_PERMIT },
81 { SYS_write, SYSTR_POLICY_PERMIT },
82 { -1, -1 }
83 };
84
85 struct ssh_sandbox {
86 int systrace_fd;
87 pid_t child_pid;
88 void (*osigchld)(int);
89 };
90
91 struct ssh_sandbox *
ssh_sandbox_init(struct monitor * monitor)92 ssh_sandbox_init(struct monitor *monitor)
93 {
94 struct ssh_sandbox *box;
95
96 debug3("%s: preparing systrace sandbox", __func__);
97 box = xcalloc(1, sizeof(*box));
98 box->systrace_fd = -1;
99 box->child_pid = 0;
100 box->osigchld = signal(SIGCHLD, SIG_IGN);
101
102 return box;
103 }
104
105 void
ssh_sandbox_child(struct ssh_sandbox * box)106 ssh_sandbox_child(struct ssh_sandbox *box)
107 {
108 debug3("%s: ready", __func__);
109 signal(SIGCHLD, box->osigchld);
110 if (kill(getpid(), SIGSTOP) != 0)
111 fatal("%s: kill(%d, SIGSTOP)", __func__, getpid());
112 debug3("%s: started", __func__);
113 }
114
115 static void
ssh_sandbox_parent(struct ssh_sandbox * box,pid_t child_pid,const struct sandbox_policy * allowed_syscalls)116 ssh_sandbox_parent(struct ssh_sandbox *box, pid_t child_pid,
117 const struct sandbox_policy *allowed_syscalls)
118 {
119 int dev_systrace, i, j, found, status;
120 pid_t pid;
121 struct systrace_policy policy;
122
123 /* Wait for the child to send itself a SIGSTOP */
124 debug3("%s: wait for child %ld", __func__, (long)child_pid);
125 do {
126 pid = waitpid(child_pid, &status, WUNTRACED);
127 } while (pid == -1 && errno == EINTR);
128 signal(SIGCHLD, box->osigchld);
129 if (!WIFSTOPPED(status)) {
130 if (WIFSIGNALED(status))
131 fatal("%s: child terminated with signal %d",
132 __func__, WTERMSIG(status));
133 if (WIFEXITED(status))
134 fatal("%s: child exited with status %d",
135 __func__, WEXITSTATUS(status));
136 fatal("%s: child not stopped", __func__);
137 }
138 debug3("%s: child %ld stopped", __func__, (long)child_pid);
139 box->child_pid = child_pid;
140
141 /* Set up systracing of child */
142 if ((dev_systrace = open("/dev/systrace", O_RDONLY)) == -1)
143 fatal("%s: open(\"/dev/systrace\"): %s", __func__,
144 strerror(errno));
145 if (ioctl(dev_systrace, STRIOCCLONE, &box->systrace_fd) == -1)
146 fatal("%s: ioctl(STRIOCCLONE, %d): %s", __func__,
147 dev_systrace, strerror(errno));
148 close(dev_systrace);
149 debug3("%s: systrace attach, fd=%d", __func__, box->systrace_fd);
150 if (ioctl(box->systrace_fd, STRIOCATTACH, &child_pid) == -1)
151 fatal("%s: ioctl(%d, STRIOCATTACH, %d): %s", __func__,
152 box->systrace_fd, child_pid, strerror(errno));
153
154 /* Allocate and assign policy */
155 memset(&policy, 0, sizeof(policy));
156 policy.strp_op = SYSTR_POLICY_NEW;
157 policy.strp_maxents = SYS_MAXSYSCALL;
158 if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1)
159 fatal("%s: ioctl(%d, STRIOCPOLICY (new)): %s", __func__,
160 box->systrace_fd, strerror(errno));
161
162 policy.strp_op = SYSTR_POLICY_ASSIGN;
163 policy.strp_pid = box->child_pid;
164 if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1)
165 fatal("%s: ioctl(%d, STRIOCPOLICY (assign)): %s",
166 __func__, box->systrace_fd, strerror(errno));
167
168 /* Set per-syscall policy */
169 for (i = 0; i < SYS_MAXSYSCALL; i++) {
170 found = 0;
171 for (j = 0; allowed_syscalls[j].syscall != -1; j++) {
172 if (allowed_syscalls[j].syscall == i) {
173 found = 1;
174 break;
175 }
176 }
177 policy.strp_op = SYSTR_POLICY_MODIFY;
178 policy.strp_code = i;
179 policy.strp_policy = found ?
180 allowed_syscalls[j].action : SYSTR_POLICY_KILL;
181 if (found)
182 debug3("%s: policy: enable syscall %d", __func__, i);
183 if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1)
184 fatal("%s: ioctl(%d, STRIOCPOLICY (modify)): %s",
185 __func__, box->systrace_fd, strerror(errno));
186 }
187
188 /* Signal the child to start running */
189 debug3("%s: start child %ld", __func__, (long)child_pid);
190 if (kill(box->child_pid, SIGCONT) != 0)
191 fatal("%s: kill(%d, SIGCONT)", __func__, box->child_pid);
192 }
193
194 void
ssh_sandbox_parent_finish(struct ssh_sandbox * box)195 ssh_sandbox_parent_finish(struct ssh_sandbox *box)
196 {
197 /* Closing this before the child exits will terminate it */
198 close(box->systrace_fd);
199
200 free(box);
201 debug3("%s: finished", __func__);
202 }
203
204 void
ssh_sandbox_parent_preauth(struct ssh_sandbox * box,pid_t child_pid)205 ssh_sandbox_parent_preauth(struct ssh_sandbox *box, pid_t child_pid)
206 {
207 ssh_sandbox_parent(box, child_pid, preauth_policy);
208 }
209
210 #endif /* SANDBOX_SYSTRACE */
211