1321807Sbapt/* $OpenBSD: sandbox-systrace.c,v 1.18 2015/10/02 01:39:26 deraadt Exp $ */ 2321807Sbapt/* 3321807Sbapt * Copyright (c) 2011 Damien Miller <djm@mindrot.org> 4321807Sbapt * 5321807Sbapt * Permission to use, copy, modify, and distribute this software for any 6321807Sbapt * purpose with or without fee is hereby granted, provided that the above 7321807Sbapt * copyright notice and this permission notice appear in all copies. 8321807Sbapt * 9321807Sbapt * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 10321807Sbapt * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 11321807Sbapt * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR 12321807Sbapt * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 13321807Sbapt * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN 14321807Sbapt * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 15321807Sbapt * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 16321807Sbapt */ 17321807Sbapt 18321807Sbapt#include "includes.h" 19321807Sbapt 20321807Sbapt#ifdef SANDBOX_SYSTRACE 21321807Sbapt 22321807Sbapt#include <sys/types.h> 23321807Sbapt#include <sys/ioctl.h> 24321807Sbapt#include <sys/syscall.h> 25321807Sbapt#include <sys/socket.h> 26321807Sbapt#include <sys/wait.h> 27321807Sbapt 28321807Sbapt#include <dev/systrace.h> 29321807Sbapt 30321807Sbapt#include <errno.h> 31321807Sbapt#include <fcntl.h> 32321807Sbapt#include <limits.h> 33321807Sbapt#include <signal.h> 34321807Sbapt#include <stdarg.h> 35321807Sbapt#include <stdio.h> 36321807Sbapt#include <stdlib.h> 37321807Sbapt#include <string.h> 38321807Sbapt#include <unistd.h> 39321807Sbapt#include <limits.h> 40321807Sbapt 41321807Sbapt#include "atomicio.h" 42321807Sbapt#include "log.h" 43321807Sbapt#include "ssh-sandbox.h" 44321807Sbapt#include "xmalloc.h" 45321807Sbapt 46321807Sbaptstruct sandbox_policy { 47321807Sbapt int syscall; 48321807Sbapt int action; 49321807Sbapt}; 50321807Sbapt 51321807Sbapt/* Permitted syscalls in preauth. Unlisted syscalls get SYSTR_POLICY_KILL */ 52321807Sbaptstatic const struct sandbox_policy preauth_policy[] = { 53321807Sbapt { SYS_exit, SYSTR_POLICY_PERMIT }, 54321807Sbapt#ifdef SYS_kbind 55321807Sbapt { SYS_kbind, SYSTR_POLICY_PERMIT }, 56321807Sbapt#endif 57321807Sbapt 58321807Sbapt { SYS_getpid, SYSTR_POLICY_PERMIT }, 59321807Sbapt { SYS_getpgid, SYSTR_POLICY_PERMIT }, 60321807Sbapt { SYS_clock_gettime, SYSTR_POLICY_PERMIT }, 61321807Sbapt { SYS_gettimeofday, SYSTR_POLICY_PERMIT }, 62321807Sbapt { SYS_sigprocmask, SYSTR_POLICY_PERMIT }, 63321807Sbapt 64321807Sbapt#ifdef SYS_getentropy 65321807Sbapt /* OpenBSD 5.6 and newer use getentropy(2) to seed arc4random(3). */ 66321807Sbapt { SYS_getentropy, SYSTR_POLICY_PERMIT }, 67321807Sbapt#else 68321807Sbapt /* Previous releases used sysctl(3)'s kern.arnd variable. */ 69321807Sbapt { SYS___sysctl, SYSTR_POLICY_PERMIT }, 70321807Sbapt#endif 71321807Sbapt#ifdef SYS_sendsyslog 72321807Sbapt { SYS_sendsyslog, SYSTR_POLICY_PERMIT }, 73321807Sbapt#endif 74321807Sbapt 75321807Sbapt { SYS_madvise, SYSTR_POLICY_PERMIT }, 76321807Sbapt { SYS_mmap, SYSTR_POLICY_PERMIT }, 77321807Sbapt { SYS_mprotect, SYSTR_POLICY_PERMIT }, 78321807Sbapt { SYS_mquery, SYSTR_POLICY_PERMIT }, 79321807Sbapt { SYS_munmap, SYSTR_POLICY_PERMIT }, 80321807Sbapt 81321807Sbapt { SYS_poll, SYSTR_POLICY_PERMIT }, 82321807Sbapt { SYS_select, SYSTR_POLICY_PERMIT }, 83321807Sbapt { SYS_read, SYSTR_POLICY_PERMIT }, 84321807Sbapt { SYS_write, SYSTR_POLICY_PERMIT }, 85321807Sbapt { SYS_shutdown, SYSTR_POLICY_PERMIT }, 86321807Sbapt { SYS_close, SYSTR_POLICY_PERMIT }, 87321807Sbapt 88321807Sbapt { SYS_open, SYSTR_POLICY_NEVER }, 89321807Sbapt 90321807Sbapt { -1, -1 } 91321807Sbapt}; 92321807Sbapt 93321807Sbaptstruct ssh_sandbox { 94321807Sbapt int systrace_fd; 95321807Sbapt pid_t child_pid; 96321807Sbapt void (*osigchld)(int); 97321807Sbapt}; 98321807Sbapt 99321807Sbaptstruct ssh_sandbox * 100321807Sbaptssh_sandbox_init(struct monitor *monitor) 101321807Sbapt{ 102321807Sbapt struct ssh_sandbox *box; 103321807Sbapt 104321807Sbapt debug3("%s: preparing systrace sandbox", __func__); 105321807Sbapt box = xcalloc(1, sizeof(*box)); 106321807Sbapt box->systrace_fd = -1; 107321807Sbapt box->child_pid = 0; 108321807Sbapt box->osigchld = signal(SIGCHLD, SIG_IGN); 109321807Sbapt 110321807Sbapt return box; 111321807Sbapt} 112321807Sbapt 113321807Sbaptvoid 114321807Sbaptssh_sandbox_child(struct ssh_sandbox *box) 115321807Sbapt{ 116321807Sbapt debug3("%s: ready", __func__); 117321807Sbapt signal(SIGCHLD, box->osigchld); 118321807Sbapt if (kill(getpid(), SIGSTOP) != 0) 119321807Sbapt fatal("%s: kill(%d, SIGSTOP)", __func__, getpid()); 120321807Sbapt debug3("%s: started", __func__); 121321807Sbapt} 122 123static void 124ssh_sandbox_parent(struct ssh_sandbox *box, pid_t child_pid, 125 const struct sandbox_policy *allowed_syscalls) 126{ 127 int dev_systrace, i, j, found, status; 128 pid_t pid; 129 struct systrace_policy policy; 130 131 /* Wait for the child to send itself a SIGSTOP */ 132 debug3("%s: wait for child %ld", __func__, (long)child_pid); 133 do { 134 pid = waitpid(child_pid, &status, WUNTRACED); 135 } while (pid == -1 && errno == EINTR); 136 signal(SIGCHLD, box->osigchld); 137 if (!WIFSTOPPED(status)) { 138 if (WIFSIGNALED(status)) 139 fatal("%s: child terminated with signal %d", 140 __func__, WTERMSIG(status)); 141 if (WIFEXITED(status)) 142 fatal("%s: child exited with status %d", 143 __func__, WEXITSTATUS(status)); 144 fatal("%s: child not stopped", __func__); 145 } 146 debug3("%s: child %ld stopped", __func__, (long)child_pid); 147 box->child_pid = child_pid; 148 149 /* Set up systracing of child */ 150 if ((dev_systrace = open("/dev/systrace", O_RDONLY)) == -1) 151 fatal("%s: open(\"/dev/systrace\"): %s", __func__, 152 strerror(errno)); 153 if (ioctl(dev_systrace, STRIOCCLONE, &box->systrace_fd) == -1) 154 fatal("%s: ioctl(STRIOCCLONE, %d): %s", __func__, 155 dev_systrace, strerror(errno)); 156 close(dev_systrace); 157 debug3("%s: systrace attach, fd=%d", __func__, box->systrace_fd); 158 if (ioctl(box->systrace_fd, STRIOCATTACH, &child_pid) == -1) 159 fatal("%s: ioctl(%d, STRIOCATTACH, %d): %s", __func__, 160 box->systrace_fd, child_pid, strerror(errno)); 161 162 /* Allocate and assign policy */ 163 memset(&policy, 0, sizeof(policy)); 164 policy.strp_op = SYSTR_POLICY_NEW; 165 policy.strp_maxents = SYS_MAXSYSCALL; 166 if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1) 167 fatal("%s: ioctl(%d, STRIOCPOLICY (new)): %s", __func__, 168 box->systrace_fd, strerror(errno)); 169 170 policy.strp_op = SYSTR_POLICY_ASSIGN; 171 policy.strp_pid = box->child_pid; 172 if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1) 173 fatal("%s: ioctl(%d, STRIOCPOLICY (assign)): %s", 174 __func__, box->systrace_fd, strerror(errno)); 175 176 /* Set per-syscall policy */ 177 for (i = 0; i < SYS_MAXSYSCALL; i++) { 178 found = 0; 179 for (j = 0; allowed_syscalls[j].syscall != -1; j++) { 180 if (allowed_syscalls[j].syscall == i) { 181 found = 1; 182 break; 183 } 184 } 185 policy.strp_op = SYSTR_POLICY_MODIFY; 186 policy.strp_code = i; 187 policy.strp_policy = found ? 188 allowed_syscalls[j].action : SYSTR_POLICY_KILL; 189 if (found) 190 debug3("%s: policy: enable syscall %d", __func__, i); 191 if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1) 192 fatal("%s: ioctl(%d, STRIOCPOLICY (modify)): %s", 193 __func__, box->systrace_fd, strerror(errno)); 194 } 195 196 /* Signal the child to start running */ 197 debug3("%s: start child %ld", __func__, (long)child_pid); 198 if (kill(box->child_pid, SIGCONT) != 0) 199 fatal("%s: kill(%d, SIGCONT)", __func__, box->child_pid); 200} 201 202void 203ssh_sandbox_parent_finish(struct ssh_sandbox *box) 204{ 205 /* Closing this before the child exits will terminate it */ 206 close(box->systrace_fd); 207 208 free(box); 209 debug3("%s: finished", __func__); 210} 211 212void 213ssh_sandbox_parent_preauth(struct ssh_sandbox *box, pid_t child_pid) 214{ 215 ssh_sandbox_parent(box, child_pid, preauth_policy); 216} 217 218#endif /* SANDBOX_SYSTRACE */ 219