Annotation of src/usr.bin/ssh/sandbox-systrace.c, Revision 1.13
1.13 ! djm 1: /* $OpenBSD: sandbox-systrace.c,v 1.12 2014/07/11 08:09:54 deraadt Exp $ */
1.1 djm 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 <sys/types.h>
19: #include <sys/param.h>
20: #include <sys/ioctl.h>
21: #include <sys/syscall.h>
22: #include <sys/socket.h>
1.6 markus 23: #include <sys/wait.h>
1.1 djm 24:
25: #include <dev/systrace.h>
26:
27: #include <errno.h>
28: #include <fcntl.h>
29: #include <limits.h>
1.6 markus 30: #include <signal.h>
1.1 djm 31: #include <stdarg.h>
32: #include <stdio.h>
33: #include <stdlib.h>
34: #include <string.h>
35: #include <unistd.h>
36:
37: #include "atomicio.h"
38: #include "log.h"
1.3 djm 39: #include "ssh-sandbox.h"
1.1 djm 40: #include "xmalloc.h"
41:
1.4 djm 42: struct sandbox_policy {
43: int syscall;
44: int action;
45: };
46:
47: /* Permitted syscalls in preauth. Unlisted syscalls get SYSTR_POLICY_KILL */
48: static const struct sandbox_policy preauth_policy[] = {
49: { SYS_open, SYSTR_POLICY_NEVER },
50:
1.11 matthew 51: #ifdef SYS_getentropy
52: /* OpenBSD 5.6 and newer use getentropy(2) to seed arc4random(3). */
53: { SYS_getentropy, SYSTR_POLICY_PERMIT },
54: #else
55: /* Previous releases used sysctl(3)'s kern.arnd variable. */
1.4 djm 56: { SYS___sysctl, SYSTR_POLICY_PERMIT },
1.11 matthew 57: #endif
1.13 ! djm 58: #ifdef SYS_sendsyslog
1.12 deraadt 59: { SYS_sendsyslog, SYSTR_POLICY_PERMIT },
1.13 ! djm 60: #endif
1.4 djm 61: { SYS_close, SYSTR_POLICY_PERMIT },
62: { SYS_exit, SYSTR_POLICY_PERMIT },
63: { SYS_getpid, SYSTR_POLICY_PERMIT },
64: { SYS_gettimeofday, SYSTR_POLICY_PERMIT },
1.7 dtucker 65: { SYS_clock_gettime, SYSTR_POLICY_PERMIT },
1.4 djm 66: { SYS_madvise, SYSTR_POLICY_PERMIT },
67: { SYS_mmap, SYSTR_POLICY_PERMIT },
68: { SYS_mprotect, SYSTR_POLICY_PERMIT },
1.5 dtucker 69: { SYS_mquery, SYSTR_POLICY_PERMIT },
1.4 djm 70: { SYS_poll, SYSTR_POLICY_PERMIT },
71: { SYS_munmap, SYSTR_POLICY_PERMIT },
72: { SYS_read, SYSTR_POLICY_PERMIT },
73: { SYS_select, SYSTR_POLICY_PERMIT },
1.8 djm 74: { SYS_shutdown, SYSTR_POLICY_PERMIT },
1.4 djm 75: { SYS_sigprocmask, SYSTR_POLICY_PERMIT },
76: { SYS_write, SYSTR_POLICY_PERMIT },
77: { -1, -1 }
1.1 djm 78: };
79:
80: struct ssh_sandbox {
81: int systrace_fd;
82: pid_t child_pid;
1.6 markus 83: void (*osigchld)(int);
1.1 djm 84: };
85:
86: struct ssh_sandbox *
87: ssh_sandbox_init(void)
88: {
89: struct ssh_sandbox *box;
90:
91: debug3("%s: preparing systrace sandbox", __func__);
92: box = xcalloc(1, sizeof(*box));
93: box->systrace_fd = -1;
94: box->child_pid = 0;
1.6 markus 95: box->osigchld = signal(SIGCHLD, SIG_IGN);
1.1 djm 96:
97: return box;
98: }
99:
100: void
101: ssh_sandbox_child(struct ssh_sandbox *box)
102: {
103: debug3("%s: ready", __func__);
1.6 markus 104: signal(SIGCHLD, box->osigchld);
105: if (kill(getpid(), SIGSTOP) != 0)
106: fatal("%s: kill(%d, SIGSTOP)", __func__, getpid());
1.1 djm 107: debug3("%s: started", __func__);
108: }
109:
110: static void
111: ssh_sandbox_parent(struct ssh_sandbox *box, pid_t child_pid,
1.4 djm 112: const struct sandbox_policy *allowed_syscalls)
1.1 djm 113: {
1.6 markus 114: int dev_systrace, i, j, found, status;
115: pid_t pid;
1.4 djm 116: struct systrace_policy policy;
1.1 djm 117:
1.6 markus 118: /* Wait for the child to send itself a SIGSTOP */
1.1 djm 119: debug3("%s: wait for child %ld", __func__, (long)child_pid);
1.6 markus 120: do {
121: pid = waitpid(child_pid, &status, WUNTRACED);
122: } while (pid == -1 && errno == EINTR);
123: signal(SIGCHLD, box->osigchld);
124: if (!WIFSTOPPED(status)) {
125: if (WIFSIGNALED(status))
126: fatal("%s: child terminated with signal %d",
127: __func__, WTERMSIG(status));
128: if (WIFEXITED(status))
129: fatal("%s: child exited with status %d",
130: __func__, WEXITSTATUS(status));
131: fatal("%s: child not stopped", __func__);
132: }
133: debug3("%s: child %ld stopped", __func__, (long)child_pid);
1.1 djm 134: box->child_pid = child_pid;
135:
136: /* Set up systracing of child */
137: if ((dev_systrace = open("/dev/systrace", O_RDONLY)) == -1)
138: fatal("%s: open(\"/dev/systrace\"): %s", __func__,
139: strerror(errno));
140: if (ioctl(dev_systrace, STRIOCCLONE, &box->systrace_fd) == -1)
141: fatal("%s: ioctl(STRIOCCLONE, %d): %s", __func__,
142: dev_systrace, strerror(errno));
143: close(dev_systrace);
144: debug3("%s: systrace attach, fd=%d", __func__, box->systrace_fd);
145: if (ioctl(box->systrace_fd, STRIOCATTACH, &child_pid) == -1)
146: fatal("%s: ioctl(%d, STRIOCATTACH, %d): %s", __func__,
147: box->systrace_fd, child_pid, strerror(errno));
148:
149: /* Allocate and assign policy */
1.9 tedu 150: memset(&policy, 0, sizeof(policy));
1.4 djm 151: policy.strp_op = SYSTR_POLICY_NEW;
152: policy.strp_maxents = SYS_MAXSYSCALL;
153: if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1)
1.1 djm 154: fatal("%s: ioctl(%d, STRIOCPOLICY (new)): %s", __func__,
155: box->systrace_fd, strerror(errno));
156:
1.4 djm 157: policy.strp_op = SYSTR_POLICY_ASSIGN;
158: policy.strp_pid = box->child_pid;
159: if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1)
1.1 djm 160: fatal("%s: ioctl(%d, STRIOCPOLICY (assign)): %s",
161: __func__, box->systrace_fd, strerror(errno));
162:
163: /* Set per-syscall policy */
164: for (i = 0; i < SYS_MAXSYSCALL; i++) {
1.4 djm 165: found = 0;
166: for (j = 0; allowed_syscalls[j].syscall != -1; j++) {
167: if (allowed_syscalls[j].syscall == i) {
1.1 djm 168: found = 1;
1.4 djm 169: break;
170: }
1.1 djm 171: }
1.4 djm 172: policy.strp_op = SYSTR_POLICY_MODIFY;
173: policy.strp_code = i;
174: policy.strp_policy = found ?
175: allowed_syscalls[j].action : SYSTR_POLICY_KILL;
1.1 djm 176: if (found)
177: debug3("%s: policy: enable syscall %d", __func__, i);
1.4 djm 178: if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1)
1.1 djm 179: fatal("%s: ioctl(%d, STRIOCPOLICY (modify)): %s",
180: __func__, box->systrace_fd, strerror(errno));
181: }
182:
183: /* Signal the child to start running */
184: debug3("%s: start child %ld", __func__, (long)child_pid);
1.6 markus 185: if (kill(box->child_pid, SIGCONT) != 0)
186: fatal("%s: kill(%d, SIGCONT)", __func__, box->child_pid);
1.1 djm 187: }
188:
189: void
190: ssh_sandbox_parent_finish(struct ssh_sandbox *box)
191: {
192: /* Closing this before the child exits will terminate it */
193: close(box->systrace_fd);
194:
195: free(box);
196: debug3("%s: finished", __func__);
197: }
198:
199: void
200: ssh_sandbox_parent_preauth(struct ssh_sandbox *box, pid_t child_pid)
201: {
202: ssh_sandbox_parent(box, child_pid, preauth_policy);
203: }
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