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 * 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 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 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 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 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