362 lines
8.5 KiB
C
362 lines
8.5 KiB
C
/* $OpenBSD: privsep.c,v 1.21 2012/08/07 20:13:18 matthieu Exp $ */
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/*
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* Copyright 2001 Niels Provos <provos@citi.umich.edu>
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* All rights reserved.
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*
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* Copyright (c) 2002 Matthieu Herrb
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* - Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* - Redistributions in binary form must reproduce the above
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* copyright notice, this list of conditions and the following
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* disclaimer in the documentation and/or other materials provided
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* with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*/
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#ifdef HAVE_DIX_CONFIG_H
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#include <dix-config.h>
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#endif
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#include <sys/param.h>
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#include <sys/uio.h>
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#include <sys/types.h>
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#include <sys/socket.h>
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#include <sys/stat.h>
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#include <err.h>
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#include <errno.h>
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#include <fcntl.h>
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#include <signal.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <unistd.h>
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#include "os.h"
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enum cmd_types {
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PRIV_OPEN_DEVICE,
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PRIV_SIG_PARENT,
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};
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/* Command parameters */
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typedef struct priv_cmd {
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int cmd;
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int _pad;
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union {
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struct _open {
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char path[MAXPATHLEN];
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} open;
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} arg;
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} priv_cmd_t;
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static int priv_fd = -1;
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static pid_t parent_pid = -1;
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struct okdev {
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const char *const name;
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int flags;
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} allowed_devices[] = {
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/* Serial devices */
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{"/dev/wsmouse", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/wsmouse0", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/wsmouse1", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/wsmouse2", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/wsmouse3", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/uhid0", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/uhid1", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/uhid2", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/uhid3", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/tty00", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/tty01", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/tty02", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/tty03", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/tty04", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/ttya", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/ttyb", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/ttyc", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/ttyd", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/wskbd", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/wskbd0", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/wskbd1", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/wskbd2", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/wskbd3", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/ttyC0", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/ttyC1", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/ttyC2", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/ttyC3", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/ttyC4", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/ttyC5", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/ttyC6", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/ttyC7", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/ttyD0", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/ttyD1", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/ttyD2", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/ttyD3", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/ttyD4", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/ttyD5", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/ttyD6", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/ttyD7", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/pci", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/agp0", O_RDWR | O_NONBLOCK | O_EXCL},
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{"/dev/drm0", O_RDWR },
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{"/dev/amdmsr", O_RDWR | O_EXCL},
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{NULL, 0}
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};
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/* return 1 if allowed to open said path */
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static struct okdev *
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open_ok(const char *path)
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{
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struct okdev *p;
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struct stat sb;
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for (p = allowed_devices; p->name != NULL; p++) {
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if (strcmp(path, p->name) == 0) {
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if (stat(path, &sb) < 0) {
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/* path is valid, but doesn't exist */
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return NULL;
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}
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if (sb.st_mode & S_IFCHR) {
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/* File is a character device */
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return p;
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}
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}
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}
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/* path is not valid */
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return NULL;
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}
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static void
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send_fd(int s, int fd)
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{
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struct msghdr msg;
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union {
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struct cmsghdr hdr;
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char buf[CMSG_SPACE(sizeof(int))];
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} cmsgbuf;
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struct cmsghdr *cmsg;
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struct iovec vec;
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int result = 0;
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ssize_t n;
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memset(&msg, 0, sizeof(msg));
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if (fd >= 0) {
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msg.msg_control = &cmsgbuf.buf;
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msg.msg_controllen = sizeof(cmsgbuf.buf);
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cmsg = CMSG_FIRSTHDR(&msg);
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cmsg->cmsg_len = CMSG_LEN(sizeof(int));
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cmsg->cmsg_level = SOL_SOCKET;
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cmsg->cmsg_type = SCM_RIGHTS;
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*(int *)CMSG_DATA(cmsg) = fd;
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} else {
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result = errno;
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}
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vec.iov_base = &result;
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vec.iov_len = sizeof(int);
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msg.msg_iov = &vec;
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msg.msg_iovlen = 1;
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if ((n = sendmsg(s, &msg, 0)) == -1)
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warn("%s: sendmsg(%d)", __func__, s);
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if (n != sizeof(int))
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warnx("%s: sendmsg: expected sent 1 got %ld",
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__func__, (long)n);
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}
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static int
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receive_fd(int s)
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{
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struct msghdr msg;
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union {
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struct cmsghdr hdr;
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char buf[CMSG_SPACE(sizeof(int))];
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} cmsgbuf;
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struct cmsghdr *cmsg;
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struct iovec vec;
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ssize_t n;
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int result;
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int fd;
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memset(&msg, 0, sizeof(msg));
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vec.iov_base = &result;
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vec.iov_len = sizeof(int);
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msg.msg_iov = &vec;
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msg.msg_iovlen = 1;
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msg.msg_control = &cmsgbuf.buf;
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msg.msg_controllen = sizeof(cmsgbuf.buf);
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do
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n = recvmsg(s, &msg, 0);
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while (n == -1 && errno == EINTR);
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if (n != sizeof(int)) {
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warnx("%s: recvmsg: expected received 1 got %ld",
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__func__, (long)n);
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return -1;
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}
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if (result == 0) {
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cmsg = CMSG_FIRSTHDR(&msg);
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if (cmsg == NULL) {
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warnx("%s: no message header", __func__);
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return -1;
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}
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if (cmsg->cmsg_type != SCM_RIGHTS)
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warnx("%s: expected type %d got %d", __func__,
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SCM_RIGHTS, cmsg->cmsg_type);
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fd = (*(int *)CMSG_DATA(cmsg));
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return fd;
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} else {
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errno = result;
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return -1;
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}
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}
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int
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priv_init(uid_t uid, gid_t gid)
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{
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int i, fd;
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pid_t pid;
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int socks[2];
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priv_cmd_t cmd;
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struct okdev *dev;
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parent_pid = getppid();
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/* Create sockets */
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if (socketpair(AF_LOCAL, SOCK_STREAM, PF_UNSPEC, socks) == -1) {
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return -1;
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}
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pid = fork();
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if (pid < 0) {
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/* can't fork */
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return -1;
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}
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if (pid != 0) {
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/* Father - drop privileges and return */
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if (setgroups(1, &gid) == -1)
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return -1;
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if (setegid(gid) == -1)
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return -1;
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if (setgid(gid) == -1)
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return -1;
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if (seteuid(uid) == -1)
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return -1;
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if (setuid(uid) == -1)
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return -1;
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close(socks[0]);
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priv_fd = socks[1];
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return 0;
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}
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/* son */
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for (i = 1; i <= _NSIG; i++)
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signal(i, SIG_DFL);
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setproctitle("[priv]");
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close(socks[1]);
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while (1) {
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if (read(socks[0], &cmd, sizeof(cmd)) == 0) {
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exit(0);
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}
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switch (cmd.cmd) {
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case PRIV_OPEN_DEVICE:
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if ((dev = open_ok(cmd.arg.open.path)) != NULL) {
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fd = open(cmd.arg.open.path, dev->flags);
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} else {
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fd = -1;
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errno = EPERM;
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}
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send_fd(socks[0], fd);
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if (fd >= 0)
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close(fd);
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break;
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case PRIV_SIG_PARENT:
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kill(parent_pid, SIGUSR1);
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break;
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default:
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errx(1, "%s: unknown command %d", __func__, cmd.cmd);
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break;
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}
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}
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_exit(1);
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}
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/* Open file */
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int
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priv_open_device(const char *path)
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{
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priv_cmd_t cmd;
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struct okdev *dev;
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if (priv_fd != -1) {
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cmd.cmd = PRIV_OPEN_DEVICE;
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strlcpy(cmd.arg.open.path, path, MAXPATHLEN);
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write(priv_fd, &cmd, sizeof(cmd));
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return receive_fd(priv_fd);
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} else {
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if ((dev = open_ok(path)) != NULL)
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return open(path, dev->flags);
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else {
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errno = EPERM;
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return -1;
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}
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}
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}
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/* send signal to parent process */
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int
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priv_signal_parent(void)
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{
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priv_cmd_t cmd;
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if (priv_fd != -1) {
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if (parent_pid == -1) {
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warnx("parent_pid == -1");
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return -1;
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}
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cmd.cmd = PRIV_SIG_PARENT;
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write(priv_fd, &cmd, sizeof(cmd));
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return 0;
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} else
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return kill(getppid(), SIGUSR1);
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}
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#ifdef TEST
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/* This is not a complete regression test */
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int
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main(int argc, char *argv[])
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{
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int fd;
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if (priv_init(getuid(), getgid()) < 0) {
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err(1, "priv_init");
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}
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fd = priv_open_device("/dev/wsmouse");
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if (fd < 0) {
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err(1, "priv_open_device");
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}
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write(fd, "test\n", 5);
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close(fd);
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exit(0);
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}
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#endif
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