sandbox-systrace.c revision 262566
1/* $OpenBSD: sandbox-systrace.c,v 1.7 2013/06/01 13:15:52 dtucker 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 46struct sandbox_policy { 47 int syscall; 48 int action; 49}; 50 51/* Permitted syscalls in preauth. Unlisted syscalls get SYSTR_POLICY_KILL */ 52static 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_sigprocmask, SYSTR_POLICY_PERMIT }, 70 { SYS_write, SYSTR_POLICY_PERMIT }, 71 { -1, -1 } 72}; 73 74struct ssh_sandbox { 75 int systrace_fd; 76 pid_t child_pid; 77 void (*osigchld)(int); 78}; 79 80struct ssh_sandbox * 81ssh_sandbox_init(struct monitor *monitor) 82{ 83 struct ssh_sandbox *box; 84 85 debug3("%s: preparing systrace sandbox", __func__); 86 box = xcalloc(1, sizeof(*box)); 87 box->systrace_fd = -1; 88 box->child_pid = 0; 89 box->osigchld = signal(SIGCHLD, SIG_IGN); 90 91 return box; 92} 93 94void 95ssh_sandbox_child(struct ssh_sandbox *box) 96{ 97 debug3("%s: ready", __func__); 98 signal(SIGCHLD, box->osigchld); 99 if (kill(getpid(), SIGSTOP) != 0) 100 fatal("%s: kill(%d, SIGSTOP)", __func__, getpid()); 101 debug3("%s: started", __func__); 102} 103 104static void 105ssh_sandbox_parent(struct ssh_sandbox *box, pid_t child_pid, 106 const struct sandbox_policy *allowed_syscalls) 107{ 108 int dev_systrace, i, j, found, status; 109 pid_t pid; 110 struct systrace_policy policy; 111 112 /* Wait for the child to send itself a SIGSTOP */ 113 debug3("%s: wait for child %ld", __func__, (long)child_pid); 114 do { 115 pid = waitpid(child_pid, &status, WUNTRACED); 116 } while (pid == -1 && errno == EINTR); 117 signal(SIGCHLD, box->osigchld); 118 if (!WIFSTOPPED(status)) { 119 if (WIFSIGNALED(status)) 120 fatal("%s: child terminated with signal %d", 121 __func__, WTERMSIG(status)); 122 if (WIFEXITED(status)) 123 fatal("%s: child exited with status %d", 124 __func__, WEXITSTATUS(status)); 125 fatal("%s: child not stopped", __func__); 126 } 127 debug3("%s: child %ld stopped", __func__, (long)child_pid); 128 box->child_pid = child_pid; 129 130 /* Set up systracing of child */ 131 if ((dev_systrace = open("/dev/systrace", O_RDONLY)) == -1) 132 fatal("%s: open(\"/dev/systrace\"): %s", __func__, 133 strerror(errno)); 134 if (ioctl(dev_systrace, STRIOCCLONE, &box->systrace_fd) == -1) 135 fatal("%s: ioctl(STRIOCCLONE, %d): %s", __func__, 136 dev_systrace, strerror(errno)); 137 close(dev_systrace); 138 debug3("%s: systrace attach, fd=%d", __func__, box->systrace_fd); 139 if (ioctl(box->systrace_fd, STRIOCATTACH, &child_pid) == -1) 140 fatal("%s: ioctl(%d, STRIOCATTACH, %d): %s", __func__, 141 box->systrace_fd, child_pid, strerror(errno)); 142 143 /* Allocate and assign policy */ 144 bzero(&policy, sizeof(policy)); 145 policy.strp_op = SYSTR_POLICY_NEW; 146 policy.strp_maxents = SYS_MAXSYSCALL; 147 if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1) 148 fatal("%s: ioctl(%d, STRIOCPOLICY (new)): %s", __func__, 149 box->systrace_fd, strerror(errno)); 150 151 policy.strp_op = SYSTR_POLICY_ASSIGN; 152 policy.strp_pid = box->child_pid; 153 if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1) 154 fatal("%s: ioctl(%d, STRIOCPOLICY (assign)): %s", 155 __func__, box->systrace_fd, strerror(errno)); 156 157 /* Set per-syscall policy */ 158 for (i = 0; i < SYS_MAXSYSCALL; i++) { 159 found = 0; 160 for (j = 0; allowed_syscalls[j].syscall != -1; j++) { 161 if (allowed_syscalls[j].syscall == i) { 162 found = 1; 163 break; 164 } 165 } 166 policy.strp_op = SYSTR_POLICY_MODIFY; 167 policy.strp_code = i; 168 policy.strp_policy = found ? 169 allowed_syscalls[j].action : SYSTR_POLICY_KILL; 170 if (found) 171 debug3("%s: policy: enable syscall %d", __func__, i); 172 if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1) 173 fatal("%s: ioctl(%d, STRIOCPOLICY (modify)): %s", 174 __func__, box->systrace_fd, strerror(errno)); 175 } 176 177 /* Signal the child to start running */ 178 debug3("%s: start child %ld", __func__, (long)child_pid); 179 if (kill(box->child_pid, SIGCONT) != 0) 180 fatal("%s: kill(%d, SIGCONT)", __func__, box->child_pid); 181} 182 183void 184ssh_sandbox_parent_finish(struct ssh_sandbox *box) 185{ 186 /* Closing this before the child exits will terminate it */ 187 close(box->systrace_fd); 188 189 free(box); 190 debug3("%s: finished", __func__); 191} 192 193void 194ssh_sandbox_parent_preauth(struct ssh_sandbox *box, pid_t child_pid) 195{ 196 ssh_sandbox_parent(box, child_pid, preauth_policy); 197} 198 199#endif /* SANDBOX_SYSTRACE */ 200