1 /* $OpenBSD: sandbox-systrace.c,v 1.9 2014/01/31 16:39:19 tedu 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/param.h>
24 #include <sys/ioctl.h>
25 #include <sys/syscall.h>
26 #include <sys/socket.h>
27 #include <sys/wait.h>
28
29 #include <dev/systrace.h>
30
31 #include <errno.h>
32 #include <fcntl.h>
33 #include <limits.h>
34 #include <signal.h>
35 #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"
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 { 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 },
60 { SYS_clock_gettime, SYSTR_POLICY_PERMIT },
61 { SYS_madvise, SYSTR_POLICY_PERMIT },
62 { SYS_mmap, SYSTR_POLICY_PERMIT },
63 { SYS_mprotect, SYSTR_POLICY_PERMIT },
64 { SYS_mquery, SYSTR_POLICY_PERMIT },
65 { 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_shutdown, SYSTR_POLICY_PERMIT },
70 { SYS_sigprocmask, SYSTR_POLICY_PERMIT },
71 { SYS_write, SYSTR_POLICY_PERMIT },
72 { -1, -1 }
73 };
74
75 struct ssh_sandbox {
76 int systrace_fd;
77 pid_t child_pid;
78 void (*osigchld)(int);
79 };
80
81 struct ssh_sandbox *
ssh_sandbox_init(struct monitor * monitor)82 ssh_sandbox_init(struct monitor *monitor)
83 {
84 struct ssh_sandbox *box;
85
86 debug3("%s: preparing systrace sandbox", __func__);
87 box = xcalloc(1, sizeof(*box));
88 box->systrace_fd = -1;
89 box->child_pid = 0;
90 box->osigchld = signal(SIGCHLD, SIG_IGN);
91
92 return box;
93 }
94
95 void
ssh_sandbox_child(struct ssh_sandbox * box)96 ssh_sandbox_child(struct ssh_sandbox *box)
97 {
98 debug3("%s: ready", __func__);
99 signal(SIGCHLD, box->osigchld);
100 if (kill(getpid(), SIGSTOP) != 0)
101 fatal("%s: kill(%d, SIGSTOP)", __func__, getpid());
102 debug3("%s: started", __func__);
103 }
104
105 static void
ssh_sandbox_parent(struct ssh_sandbox * box,pid_t child_pid,const struct sandbox_policy * allowed_syscalls)106 ssh_sandbox_parent(struct ssh_sandbox *box, pid_t child_pid,
107 const struct sandbox_policy *allowed_syscalls)
108 {
109 int dev_systrace, i, j, found, status;
110 pid_t pid;
111 struct systrace_policy policy;
112
113 /* Wait for the child to send itself a SIGSTOP */
114 debug3("%s: wait for child %ld", __func__, (long)child_pid);
115 do {
116 pid = waitpid(child_pid, &status, WUNTRACED);
117 } while (pid == -1 && errno == EINTR);
118 signal(SIGCHLD, box->osigchld);
119 if (!WIFSTOPPED(status)) {
120 if (WIFSIGNALED(status))
121 fatal("%s: child terminated with signal %d",
122 __func__, WTERMSIG(status));
123 if (WIFEXITED(status))
124 fatal("%s: child exited with status %d",
125 __func__, WEXITSTATUS(status));
126 fatal("%s: child not stopped", __func__);
127 }
128 debug3("%s: child %ld stopped", __func__, (long)child_pid);
129 box->child_pid = child_pid;
130
131 /* Set up systracing of child */
132 if ((dev_systrace = open("/dev/systrace", O_RDONLY)) == -1)
133 fatal("%s: open(\"/dev/systrace\"): %s", __func__,
134 strerror(errno));
135 if (ioctl(dev_systrace, STRIOCCLONE, &box->systrace_fd) == -1)
136 fatal("%s: ioctl(STRIOCCLONE, %d): %s", __func__,
137 dev_systrace, strerror(errno));
138 close(dev_systrace);
139 debug3("%s: systrace attach, fd=%d", __func__, box->systrace_fd);
140 if (ioctl(box->systrace_fd, STRIOCATTACH, &child_pid) == -1)
141 fatal("%s: ioctl(%d, STRIOCATTACH, %d): %s", __func__,
142 box->systrace_fd, child_pid, strerror(errno));
143
144 /* Allocate and assign policy */
145 memset(&policy, 0, sizeof(policy));
146 policy.strp_op = SYSTR_POLICY_NEW;
147 policy.strp_maxents = SYS_MAXSYSCALL;
148 if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1)
149 fatal("%s: ioctl(%d, STRIOCPOLICY (new)): %s", __func__,
150 box->systrace_fd, strerror(errno));
151
152 policy.strp_op = SYSTR_POLICY_ASSIGN;
153 policy.strp_pid = box->child_pid;
154 if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1)
155 fatal("%s: ioctl(%d, STRIOCPOLICY (assign)): %s",
156 __func__, box->systrace_fd, strerror(errno));
157
158 /* Set per-syscall policy */
159 for (i = 0; i < SYS_MAXSYSCALL; i++) {
160 found = 0;
161 for (j = 0; allowed_syscalls[j].syscall != -1; j++) {
162 if (allowed_syscalls[j].syscall == i) {
163 found = 1;
164 break;
165 }
166 }
167 policy.strp_op = SYSTR_POLICY_MODIFY;
168 policy.strp_code = i;
169 policy.strp_policy = found ?
170 allowed_syscalls[j].action : SYSTR_POLICY_KILL;
171 if (found)
172 debug3("%s: policy: enable syscall %d", __func__, i);
173 if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1)
174 fatal("%s: ioctl(%d, STRIOCPOLICY (modify)): %s",
175 __func__, box->systrace_fd, strerror(errno));
176 }
177
178 /* Signal the child to start running */
179 debug3("%s: start child %ld", __func__, (long)child_pid);
180 if (kill(box->child_pid, SIGCONT) != 0)
181 fatal("%s: kill(%d, SIGCONT)", __func__, box->child_pid);
182 }
183
184 void
ssh_sandbox_parent_finish(struct ssh_sandbox * box)185 ssh_sandbox_parent_finish(struct ssh_sandbox *box)
186 {
187 /* Closing this before the child exits will terminate it */
188 close(box->systrace_fd);
189
190 free(box);
191 debug3("%s: finished", __func__);
192 }
193
194 void
ssh_sandbox_parent_preauth(struct ssh_sandbox * box,pid_t child_pid)195 ssh_sandbox_parent_preauth(struct ssh_sandbox *box, pid_t child_pid)
196 {
197 ssh_sandbox_parent(box, child_pid, preauth_policy);
198 }
199
200 #endif /* SANDBOX_SYSTRACE */
201