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vlc/bin/rootwrap.c

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/*****************************************************************************
* rootwrap.c
*****************************************************************************
* Copyright © 2005-2008 Rémi Denis-Courmont
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
*****************************************************************************/
#ifdef HAVE_CONFIG_H
# include <config.h>
#endif
#define _XPG4_2 /* ancilliary data on Solaris */
#include <stdlib.h> /* exit() */
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <sys/uio.h>
#include <sys/resource.h> /* getrlimit() */
#ifdef RLIMIT_RTPRIO
#include <sched.h>
#endif
#include <errno.h>
#include <netinet/in.h>
#if defined (AF_INET6) && !defined (IPV6_V6ONLY)
# warning Uho, your IPv6 support is broken and has been disabled. Fix your C library.
# undef AF_INET6
#endif
#ifndef AF_LOCAL
# define AF_LOCAL AF_UNIX
#endif
#if !defined(MSG_NOSIGNAL) && defined(SO_NOSIGPIPE)
# define MSG_NOSIGNAL 0
#endif
/* Required yet non-standard cmsg functions */
#ifndef CMSG_ALIGN
# define CMSG_ALIGN(len) (((len) + sizeof(intptr_t)-1) & ~(sizeof(intptr_t)-1))
#endif
#ifndef CMSG_SPACE
# define CMSG_SPACE(len) (CMSG_ALIGN(sizeof(struct cmsghdr)) + CMSG_ALIGN(len))
#endif
#ifndef CMSG_LEN
# define CMSG_LEN(len) (CMSG_ALIGN(sizeof(struct cmsghdr)) + (len))
#endif
static inline int is_allowed_port (uint16_t port)
{
port = ntohs (port);
return (port == 80) || (port == 443) || (port == 554);
}
static inline int send_err (int fd, int err)
{
return send(fd, &err, sizeof (err), MSG_NOSIGNAL) == sizeof (err) ? 0 : -1;
}
/**
* Send a file descriptor to another process
*/
static int send_fd (int p, int fd)
{
struct msghdr hdr;
struct iovec iov;
struct cmsghdr *cmsg;
char buf[CMSG_SPACE (sizeof (fd))];
int val = 0;
hdr.msg_name = NULL;
hdr.msg_namelen = 0;
hdr.msg_iov = &iov;
hdr.msg_iovlen = 1;
hdr.msg_control = buf;
hdr.msg_controllen = sizeof (buf);
iov.iov_base = &val;
iov.iov_len = sizeof (val);
cmsg = CMSG_FIRSTHDR (&hdr);
cmsg->cmsg_level = SOL_SOCKET;
cmsg->cmsg_type = SCM_RIGHTS;
cmsg->cmsg_len = CMSG_LEN (sizeof (fd));
memcpy (CMSG_DATA (cmsg), &fd, sizeof (fd));
hdr.msg_controllen = cmsg->cmsg_len;
return sendmsg(p, &hdr, MSG_NOSIGNAL) == sizeof (val) ? 0 : -1;
}
/**
* Background process run as root to open privileged TCP ports.
*/
static void rootprocess (int fd)
{
union
{
struct sockaddr sa;
struct sockaddr_storage ss;
struct sockaddr_in sin;
#ifdef AF_INET6
struct sockaddr_in6 sin6;
#endif
} addr;
while (recv (fd, &addr.ss, sizeof (addr.ss), 0) == sizeof (addr.ss))
{
unsigned len;
int sock;
int family;
switch (addr.sa.sa_family)
{
case AF_INET:
if (!is_allowed_port (addr.sin.sin_port))
{
if (send_err (fd, EACCES))
return;
continue;
}
len = sizeof (struct sockaddr_in);
family = PF_INET;
break;
#ifdef AF_INET6
case AF_INET6:
if (!is_allowed_port (addr.sin6.sin6_port))
{
if (send_err (fd, EACCES))
return;
continue;
}
len = sizeof (struct sockaddr_in6);
family = PF_INET6;
break;
#endif
default:
if (send_err (fd, EAFNOSUPPORT))
return;
continue;
}
sock = socket (family, SOCK_STREAM, IPPROTO_TCP);
if (sock != -1)
{
setsockopt (sock, SOL_SOCKET, SO_REUSEADDR, &(int){ 1 }, sizeof (int));
#ifdef AF_INET6
if (addr.sa.sa_family == AF_INET6)
setsockopt (sock, IPPROTO_IPV6, IPV6_V6ONLY, &(int){ 1 }, sizeof (int));
#endif
if (bind (sock, &addr.sa, len) == 0)
{
send_fd (fd, sock);
close (sock);
continue;
}
close (sock);
}
send_err (fd, errno);
}
}
/* TODO?
* - use libcap if available,
* - call chroot
*/
int main (int argc, char *argv[])
{
/* Support for dynamically opening RTSP, HTTP and HTTP/SSL ports */
int pair[2];
if (socketpair (AF_LOCAL, SOCK_STREAM, 0, pair))
return 1;
if (pair[0] < 3)
goto error; /* we want 0, 1 and 2 open */
#ifdef SO_NOSIGPIPE
setsockopt(pair[1], SOL_SOCKET, SO_NOSIGPIPE, &(int){ 1 }, sizeof (int));
#endif
pid_t pid = fork ();
switch (pid)
{
case -1:
goto error;
case 0:
{
int null = open ("/dev/null", O_RDWR);
if (null != -1)
{
dup2 (null, 0);
dup2 (null, 1);
dup2 (null, 2);
close (null);
}
close (pair[0]);
setsid ();
rootprocess (pair[1]);
exit (0);
}
}
close (pair[1]);
pair[1] = -1;
char buf[21];
snprintf (buf, sizeof (buf), "%d", pair[0]);
setenv ("VLC_ROOTWRAP_SOCK", buf, 1);
/* Support for real-time priorities */
#ifdef RLIMIT_RTPRIO
struct rlimit rlim;
rlim.rlim_max = rlim.rlim_cur = sched_get_priority_min (SCHED_RR) + 24;
setrlimit (RLIMIT_RTPRIO, &rlim);
#endif
uid_t uid = getuid ();
if (uid == 0)
{
const char *sudo = getenv ("SUDO_UID");
if (sudo)
uid = atoi (sudo);
}
if (uid == 0)
{
fputs("Cannot determine unprivileged user for VLC!\n", stderr);
exit (1);
}
setuid (uid);
if (!setuid (0)) /* sanity check: we cannot get root back */
exit (1);
/* Yeah, the user can execute just about anything from here.
* But we've dropped privileges, so it does not matter. */
if (strlen (argv[0]) < sizeof ("-wrapper"))
goto error;
argv[0][strlen (argv[0]) - strlen ("-wrapper")] = '\0';
(void)argc;
if (execvp (argv[0], argv))
perror (argv[0]);
error:
close (pair[0]);
if (pair[1] != -1)
close (pair[1]);
return 1;
}
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