1 /* $OpenBSD: sandbox-systrace.c,v 1.16 2015/06/29 22:35:12 djm 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_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 { SYS_madvise, SYSTR_POLICY_PERMIT }, 67 { SYS_mmap, SYSTR_POLICY_PERMIT }, 68 { SYS_mprotect, SYSTR_POLICY_PERMIT }, 69 { SYS_mquery, SYSTR_POLICY_PERMIT }, 70 { SYS_munmap, SYSTR_POLICY_PERMIT }, 71 { SYS_open, SYSTR_POLICY_NEVER }, 72 { SYS_poll, SYSTR_POLICY_PERMIT }, 73 { SYS_read, SYSTR_POLICY_PERMIT }, 74 { SYS_select, SYSTR_POLICY_PERMIT }, 75 #ifdef SYS_sendsyslog 76 { SYS_sendsyslog, SYSTR_POLICY_PERMIT }, 77 #endif 78 { SYS_shutdown, SYSTR_POLICY_PERMIT }, 79 { SYS_sigprocmask, SYSTR_POLICY_PERMIT }, 80 { SYS_write, SYSTR_POLICY_PERMIT }, 81 { -1, -1 } 82 }; 83 84 struct ssh_sandbox { 85 int systrace_fd; 86 pid_t child_pid; 87 void (*osigchld)(int); 88 }; 89 90 struct ssh_sandbox * 91 ssh_sandbox_init(struct monitor *monitor) 92 { 93 struct ssh_sandbox *box; 94 95 debug3("%s: preparing systrace sandbox", __func__); 96 box = xcalloc(1, sizeof(*box)); 97 box->systrace_fd = -1; 98 box->child_pid = 0; 99 box->osigchld = signal(SIGCHLD, SIG_IGN); 100 101 return box; 102 } 103 104 void 105 ssh_sandbox_child(struct ssh_sandbox *box) 106 { 107 debug3("%s: ready", __func__); 108 signal(SIGCHLD, box->osigchld); 109 if (kill(getpid(), SIGSTOP) != 0) 110 fatal("%s: kill(%d, SIGSTOP)", __func__, getpid()); 111 debug3("%s: started", __func__); 112 } 113 114 static void 115 ssh_sandbox_parent(struct ssh_sandbox *box, pid_t child_pid, 116 const struct sandbox_policy *allowed_syscalls) 117 { 118 int dev_systrace, i, j, found, status; 119 pid_t pid; 120 struct systrace_policy policy; 121 122 /* Wait for the child to send itself a SIGSTOP */ 123 debug3("%s: wait for child %ld", __func__, (long)child_pid); 124 do { 125 pid = waitpid(child_pid, &status, WUNTRACED); 126 } while (pid == -1 && errno == EINTR); 127 signal(SIGCHLD, box->osigchld); 128 if (!WIFSTOPPED(status)) { 129 if (WIFSIGNALED(status)) 130 fatal("%s: child terminated with signal %d", 131 __func__, WTERMSIG(status)); 132 if (WIFEXITED(status)) 133 fatal("%s: child exited with status %d", 134 __func__, WEXITSTATUS(status)); 135 fatal("%s: child not stopped", __func__); 136 } 137 debug3("%s: child %ld stopped", __func__, (long)child_pid); 138 box->child_pid = child_pid; 139 140 /* Set up systracing of child */ 141 if ((dev_systrace = open("/dev/systrace", O_RDONLY)) == -1) 142 fatal("%s: open(\"/dev/systrace\"): %s", __func__, 143 strerror(errno)); 144 if (ioctl(dev_systrace, STRIOCCLONE, &box->systrace_fd) == -1) 145 fatal("%s: ioctl(STRIOCCLONE, %d): %s", __func__, 146 dev_systrace, strerror(errno)); 147 close(dev_systrace); 148 debug3("%s: systrace attach, fd=%d", __func__, box->systrace_fd); 149 if (ioctl(box->systrace_fd, STRIOCATTACH, &child_pid) == -1) 150 fatal("%s: ioctl(%d, STRIOCATTACH, %d): %s", __func__, 151 box->systrace_fd, child_pid, strerror(errno)); 152 153 /* Allocate and assign policy */ 154 memset(&policy, 0, sizeof(policy)); 155 policy.strp_op = SYSTR_POLICY_NEW; 156 policy.strp_maxents = SYS_MAXSYSCALL; 157 if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1) 158 fatal("%s: ioctl(%d, STRIOCPOLICY (new)): %s", __func__, 159 box->systrace_fd, strerror(errno)); 160 161 policy.strp_op = SYSTR_POLICY_ASSIGN; 162 policy.strp_pid = box->child_pid; 163 if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1) 164 fatal("%s: ioctl(%d, STRIOCPOLICY (assign)): %s", 165 __func__, box->systrace_fd, strerror(errno)); 166 167 /* Set per-syscall policy */ 168 for (i = 0; i < SYS_MAXSYSCALL; i++) { 169 found = 0; 170 for (j = 0; allowed_syscalls[j].syscall != -1; j++) { 171 if (allowed_syscalls[j].syscall == i) { 172 found = 1; 173 break; 174 } 175 } 176 policy.strp_op = SYSTR_POLICY_MODIFY; 177 policy.strp_code = i; 178 policy.strp_policy = found ? 179 allowed_syscalls[j].action : SYSTR_POLICY_KILL; 180 if (found) 181 debug3("%s: policy: enable syscall %d", __func__, i); 182 if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1) 183 fatal("%s: ioctl(%d, STRIOCPOLICY (modify)): %s", 184 __func__, box->systrace_fd, strerror(errno)); 185 } 186 187 /* Signal the child to start running */ 188 debug3("%s: start child %ld", __func__, (long)child_pid); 189 if (kill(box->child_pid, SIGCONT) != 0) 190 fatal("%s: kill(%d, SIGCONT)", __func__, box->child_pid); 191 } 192 193 void 194 ssh_sandbox_parent_finish(struct ssh_sandbox *box) 195 { 196 /* Closing this before the child exits will terminate it */ 197 close(box->systrace_fd); 198 199 free(box); 200 debug3("%s: finished", __func__); 201 } 202 203 void 204 ssh_sandbox_parent_preauth(struct ssh_sandbox *box, pid_t child_pid) 205 { 206 ssh_sandbox_parent(box, child_pid, preauth_policy); 207 } 208 209 #endif /* SANDBOX_SYSTRACE */ 210