1 /* $OpenBSD: sandbox-systrace.c,v 1.17 2015/07/27 16:29:23 guenther Exp $ */ 2 /* 3 * Copyright (c) 2011 Damien Miller <djm (at) 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_clock_gettime, SYSTR_POLICY_PERMIT }, 54 { SYS_close, SYSTR_POLICY_PERMIT }, 55 { SYS_exit, SYSTR_POLICY_PERMIT }, 56 #ifdef SYS_getentropy 57 /* OpenBSD 5.6 and newer use getentropy(2) to seed arc4random(3). */ 58 { SYS_getentropy, SYSTR_POLICY_PERMIT }, 59 #else 60 /* Previous releases used sysctl(3)'s kern.arnd variable. */ 61 { SYS___sysctl, SYSTR_POLICY_PERMIT }, 62 #endif 63 { SYS_getpid, SYSTR_POLICY_PERMIT }, 64 { SYS_getpgid, SYSTR_POLICY_PERMIT }, 65 { SYS_gettimeofday, SYSTR_POLICY_PERMIT }, 66 #ifdef SYS_kbind 67 { SYS_kbind, SYSTR_POLICY_PERMIT }, 68 #endif 69 { SYS_madvise, SYSTR_POLICY_PERMIT }, 70 { SYS_mmap, SYSTR_POLICY_PERMIT }, 71 { SYS_mprotect, SYSTR_POLICY_PERMIT }, 72 { SYS_mquery, SYSTR_POLICY_PERMIT }, 73 { SYS_munmap, SYSTR_POLICY_PERMIT }, 74 { SYS_open, SYSTR_POLICY_NEVER }, 75 { SYS_poll, SYSTR_POLICY_PERMIT }, 76 { SYS_read, SYSTR_POLICY_PERMIT }, 77 { SYS_select, SYSTR_POLICY_PERMIT }, 78 #ifdef SYS_sendsyslog 79 { SYS_sendsyslog, SYSTR_POLICY_PERMIT }, 80 #endif 81 { SYS_shutdown, SYSTR_POLICY_PERMIT }, 82 { SYS_sigprocmask, SYSTR_POLICY_PERMIT }, 83 { SYS_write, SYSTR_POLICY_PERMIT }, 84 { -1, -1 } 85 }; 86 87 struct ssh_sandbox { 88 int systrace_fd; 89 pid_t child_pid; 90 void (*osigchld)(int); 91 }; 92 93 struct ssh_sandbox * 94 ssh_sandbox_init(struct monitor *monitor) 95 { 96 struct ssh_sandbox *box; 97 98 debug3("%s: preparing systrace sandbox", __func__); 99 box = xcalloc(1, sizeof(*box)); 100 box->systrace_fd = -1; 101 box->child_pid = 0; 102 box->osigchld = signal(SIGCHLD, SIG_IGN); 103 104 return box; 105 } 106 107 void 108 ssh_sandbox_child(struct ssh_sandbox *box) 109 { 110 debug3("%s: ready", __func__); 111 signal(SIGCHLD, box->osigchld); 112 if (kill(getpid(), SIGSTOP) != 0) 113 fatal("%s: kill(%d, SIGSTOP)", __func__, getpid()); 114 debug3("%s: started", __func__); 115 } 116 117 static void 118 ssh_sandbox_parent(struct ssh_sandbox *box, pid_t child_pid, 119 const struct sandbox_policy *allowed_syscalls) 120 { 121 int dev_systrace, i, j, found, status; 122 pid_t pid; 123 struct systrace_policy policy; 124 125 /* Wait for the child to send itself a SIGSTOP */ 126 debug3("%s: wait for child %ld", __func__, (long)child_pid); 127 do { 128 pid = waitpid(child_pid, &status, WUNTRACED); 129 } while (pid == -1 && errno == EINTR); 130 signal(SIGCHLD, box->osigchld); 131 if (!WIFSTOPPED(status)) { 132 if (WIFSIGNALED(status)) 133 fatal("%s: child terminated with signal %d", 134 __func__, WTERMSIG(status)); 135 if (WIFEXITED(status)) 136 fatal("%s: child exited with status %d", 137 __func__, WEXITSTATUS(status)); 138 fatal("%s: child not stopped", __func__); 139 } 140 debug3("%s: child %ld stopped", __func__, (long)child_pid); 141 box->child_pid = child_pid; 142 143 /* Set up systracing of child */ 144 if ((dev_systrace = open("/dev/systrace", O_RDONLY)) == -1) 145 fatal("%s: open(\"/dev/systrace\"): %s", __func__, 146 strerror(errno)); 147 if (ioctl(dev_systrace, STRIOCCLONE, &box->systrace_fd) == -1) 148 fatal("%s: ioctl(STRIOCCLONE, %d): %s", __func__, 149 dev_systrace, strerror(errno)); 150 close(dev_systrace); 151 debug3("%s: systrace attach, fd=%d", __func__, box->systrace_fd); 152 if (ioctl(box->systrace_fd, STRIOCATTACH, &child_pid) == -1) 153 fatal("%s: ioctl(%d, STRIOCATTACH, %d): %s", __func__, 154 box->systrace_fd, child_pid, strerror(errno)); 155 156 /* Allocate and assign policy */ 157 memset(&policy, 0, sizeof(policy)); 158 policy.strp_op = SYSTR_POLICY_NEW; 159 policy.strp_maxents = SYS_MAXSYSCALL; 160 if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1) 161 fatal("%s: ioctl(%d, STRIOCPOLICY (new)): %s", __func__, 162 box->systrace_fd, strerror(errno)); 163 164 policy.strp_op = SYSTR_POLICY_ASSIGN; 165 policy.strp_pid = box->child_pid; 166 if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1) 167 fatal("%s: ioctl(%d, STRIOCPOLICY (assign)): %s", 168 __func__, box->systrace_fd, strerror(errno)); 169 170 /* Set per-syscall policy */ 171 for (i = 0; i < SYS_MAXSYSCALL; i++) { 172 found = 0; 173 for (j = 0; allowed_syscalls[j].syscall != -1; j++) { 174 if (allowed_syscalls[j].syscall == i) { 175 found = 1; 176 break; 177 } 178 } 179 policy.strp_op = SYSTR_POLICY_MODIFY; 180 policy.strp_code = i; 181 policy.strp_policy = found ? 182 allowed_syscalls[j].action : SYSTR_POLICY_KILL; 183 if (found) 184 debug3("%s: policy: enable syscall %d", __func__, i); 185 if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1) 186 fatal("%s: ioctl(%d, STRIOCPOLICY (modify)): %s", 187 __func__, box->systrace_fd, strerror(errno)); 188 } 189 190 /* Signal the child to start running */ 191 debug3("%s: start child %ld", __func__, (long)child_pid); 192 if (kill(box->child_pid, SIGCONT) != 0) 193 fatal("%s: kill(%d, SIGCONT)", __func__, box->child_pid); 194 } 195 196 void 197 ssh_sandbox_parent_finish(struct ssh_sandbox *box) 198 { 199 /* Closing this before the child exits will terminate it */ 200 close(box->systrace_fd); 201 202 free(box); 203 debug3("%s: finished", __func__); 204 } 205 206 void 207 ssh_sandbox_parent_preauth(struct ssh_sandbox *box, pid_t child_pid) 208 { 209 ssh_sandbox_parent(box, child_pid, preauth_policy); 210 } 211 212 #endif /* SANDBOX_SYSTRACE */ 213
