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/* $OpenBSD: sandbox-systrace.c,v 1.12 2014/07/11 08:09:54 deraadt Exp $ */
/*
* Copyright (c) 2011 Damien Miller <djm@mindrot.org>
*
* Permission to use, copy, modify, and distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
#include <sys/types.h>
#include <sys/param.h>
#include <sys/ioctl.h>
#include <sys/syscall.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <dev/systrace.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <signal.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include "atomicio.h"
#include "log.h"
#include "ssh-sandbox.h"
#include "xmalloc.h"
struct sandbox_policy {
int syscall;
int action;
};
/* Permitted syscalls in preauth. Unlisted syscalls get SYSTR_POLICY_KILL */
static const struct sandbox_policy preauth_policy[] = {
{ SYS_open, SYSTR_POLICY_NEVER },
#ifdef SYS_getentropy
/* OpenBSD 5.6 and newer use getentropy(2) to seed arc4random(3). */
{ SYS_getentropy, SYSTR_POLICY_PERMIT },
#else
/* Previous releases used sysctl(3)'s kern.arnd variable. */
{ SYS___sysctl, SYSTR_POLICY_PERMIT },
#endif
{ SYS_sendsyslog, SYSTR_POLICY_PERMIT },
{ SYS_close, SYSTR_POLICY_PERMIT },
{ SYS_exit, SYSTR_POLICY_PERMIT },
{ SYS_getpid, SYSTR_POLICY_PERMIT },
{ SYS_gettimeofday, SYSTR_POLICY_PERMIT },
{ SYS_clock_gettime, SYSTR_POLICY_PERMIT },
{ SYS_madvise, SYSTR_POLICY_PERMIT },
{ SYS_mmap, SYSTR_POLICY_PERMIT },
{ SYS_mprotect, SYSTR_POLICY_PERMIT },
{ SYS_mquery, SYSTR_POLICY_PERMIT },
{ SYS_poll, SYSTR_POLICY_PERMIT },
{ SYS_munmap, SYSTR_POLICY_PERMIT },
{ SYS_read, SYSTR_POLICY_PERMIT },
{ SYS_select, SYSTR_POLICY_PERMIT },
{ SYS_shutdown, SYSTR_POLICY_PERMIT },
{ SYS_sigprocmask, SYSTR_POLICY_PERMIT },
{ SYS_write, SYSTR_POLICY_PERMIT },
{ -1, -1 }
};
struct ssh_sandbox {
int systrace_fd;
pid_t child_pid;
void (*osigchld)(int);
};
struct ssh_sandbox *
ssh_sandbox_init(void)
{
struct ssh_sandbox *box;
debug3("%s: preparing systrace sandbox", __func__);
box = xcalloc(1, sizeof(*box));
box->systrace_fd = -1;
box->child_pid = 0;
box->osigchld = signal(SIGCHLD, SIG_IGN);
return box;
}
void
ssh_sandbox_child(struct ssh_sandbox *box)
{
debug3("%s: ready", __func__);
signal(SIGCHLD, box->osigchld);
if (kill(getpid(), SIGSTOP) != 0)
fatal("%s: kill(%d, SIGSTOP)", __func__, getpid());
debug3("%s: started", __func__);
}
static void
ssh_sandbox_parent(struct ssh_sandbox *box, pid_t child_pid,
const struct sandbox_policy *allowed_syscalls)
{
int dev_systrace, i, j, found, status;
pid_t pid;
struct systrace_policy policy;
/* Wait for the child to send itself a SIGSTOP */
debug3("%s: wait for child %ld", __func__, (long)child_pid);
do {
pid = waitpid(child_pid, &status, WUNTRACED);
} while (pid == -1 && errno == EINTR);
signal(SIGCHLD, box->osigchld);
if (!WIFSTOPPED(status)) {
if (WIFSIGNALED(status))
fatal("%s: child terminated with signal %d",
__func__, WTERMSIG(status));
if (WIFEXITED(status))
fatal("%s: child exited with status %d",
__func__, WEXITSTATUS(status));
fatal("%s: child not stopped", __func__);
}
debug3("%s: child %ld stopped", __func__, (long)child_pid);
box->child_pid = child_pid;
/* Set up systracing of child */
if ((dev_systrace = open("/dev/systrace", O_RDONLY)) == -1)
fatal("%s: open(\"/dev/systrace\"): %s", __func__,
strerror(errno));
if (ioctl(dev_systrace, STRIOCCLONE, &box->systrace_fd) == -1)
fatal("%s: ioctl(STRIOCCLONE, %d): %s", __func__,
dev_systrace, strerror(errno));
close(dev_systrace);
debug3("%s: systrace attach, fd=%d", __func__, box->systrace_fd);
if (ioctl(box->systrace_fd, STRIOCATTACH, &child_pid) == -1)
fatal("%s: ioctl(%d, STRIOCATTACH, %d): %s", __func__,
box->systrace_fd, child_pid, strerror(errno));
/* Allocate and assign policy */
memset(&policy, 0, sizeof(policy));
policy.strp_op = SYSTR_POLICY_NEW;
policy.strp_maxents = SYS_MAXSYSCALL;
if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1)
fatal("%s: ioctl(%d, STRIOCPOLICY (new)): %s", __func__,
box->systrace_fd, strerror(errno));
policy.strp_op = SYSTR_POLICY_ASSIGN;
policy.strp_pid = box->child_pid;
if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1)
fatal("%s: ioctl(%d, STRIOCPOLICY (assign)): %s",
__func__, box->systrace_fd, strerror(errno));
/* Set per-syscall policy */
for (i = 0; i < SYS_MAXSYSCALL; i++) {
found = 0;
for (j = 0; allowed_syscalls[j].syscall != -1; j++) {
if (allowed_syscalls[j].syscall == i) {
found = 1;
break;
}
}
policy.strp_op = SYSTR_POLICY_MODIFY;
policy.strp_code = i;
policy.strp_policy = found ?
allowed_syscalls[j].action : SYSTR_POLICY_KILL;
if (found)
debug3("%s: policy: enable syscall %d", __func__, i);
if (ioctl(box->systrace_fd, STRIOCPOLICY, &policy) == -1)
fatal("%s: ioctl(%d, STRIOCPOLICY (modify)): %s",
__func__, box->systrace_fd, strerror(errno));
}
/* Signal the child to start running */
debug3("%s: start child %ld", __func__, (long)child_pid);
if (kill(box->child_pid, SIGCONT) != 0)
fatal("%s: kill(%d, SIGCONT)", __func__, box->child_pid);
}
void
ssh_sandbox_parent_finish(struct ssh_sandbox *box)
{
/* Closing this before the child exits will terminate it */
close(box->systrace_fd);
free(box);
debug3("%s: finished", __func__);
}
void
ssh_sandbox_parent_preauth(struct ssh_sandbox *box, pid_t child_pid)
{
ssh_sandbox_parent(box, child_pid, preauth_policy);
}
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