bin/rootwrap.c

   1 /*****************************************************************************
   2  * rootwrap.c
   3  *****************************************************************************
   4  * Copyright © 2005-2008 Rémi Denis-Courmont
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License as published by
   8  * the Free Software Foundation; either version 2 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program; if not, write to the Free Software
  18  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
  19  *****************************************************************************/
  20
  21 #ifdef HAVE_CONFIG_H
  22 # include <config.h>
  23 #endif
  24 #define _XPG4_2 /* ancilliary data on Solaris */
  25
  26 #include <stdlib.h> /* exit() */
  27 #include <stdio.h>
  28 #include <string.h>
  29
  30 #include <sys/types.h>
  31 #include <unistd.h>
  32 #include <fcntl.h>
  33 #include <sys/stat.h>
  34 #include <sys/socket.h>
  35 #include <sys/uio.h>
  36 #include <sys/resource.h> /* getrlimit() */
  37 #ifdef RLIMIT_RTPRIO
  38 #include <sched.h>
  39 #endif
  40 #include <errno.h>
  41 #include <netinet/in.h>
  42
  43 #if defined (AF_INET6) && !defined (IPV6_V6ONLY)
  44 # warning Uho, your IPv6 support is broken and has been disabled. Fix your C library.
  45 # undef AF_INET6
  46 #endif
  47 #ifndef AF_LOCAL
  48 # define AF_LOCAL AF_UNIX
  49 #endif
  50 #if !defined(MSG_NOSIGNAL) && defined(SO_NOSIGPIPE)
  51 # define MSG_NOSIGNAL 0
  52 #endif
  53 /* Required yet non-standard cmsg functions */
  54 #ifndef CMSG_ALIGN
  55 # define CMSG_ALIGN(len) (((len) + sizeof(intptr_t)-1) & ~(sizeof(intptr_t)-1))
  56 #endif
  57 #ifndef CMSG_SPACE
  58 # define CMSG_SPACE(len) (CMSG_ALIGN(sizeof(struct cmsghdr)) + CMSG_ALIGN(len))
  59 #endif
  60 #ifndef CMSG_LEN
  61 # define CMSG_LEN(len) (CMSG_ALIGN(sizeof(struct cmsghdr)) + (len))
  62 #endif
  63
  64 static inline int is_allowed_port (uint16_t port)
  65 {
  66     port = ntohs (port);
  67     return (port == 80) || (port == 443) || (port == 554);
  68 }
  69
  70
  71 static inline int send_err (int fd, int err)
  72 {
  73     return send(fd, &err, sizeof (err), MSG_NOSIGNAL) == sizeof (err) ? 0 : -1;
  74 }
  75
  76 /**
  77  * Send a file descriptor to another process
  78  */
  79 static int send_fd (int p, int fd)
  80 {
  81     struct msghdr hdr;
  82     struct iovec iov;
  83     struct cmsghdr *cmsg;
  84     char buf[CMSG_SPACE (sizeof (fd))];
  85     int val = 0;
  86
  87     hdr.msg_name = NULL;
  88     hdr.msg_namelen = 0;
  89     hdr.msg_iov = &iov;
  90     hdr.msg_iovlen = 1;
  91     hdr.msg_control = buf;
  92     hdr.msg_controllen = sizeof (buf);
  93
  94     iov.iov_base = &val;
  95     iov.iov_len = sizeof (val);
  96
  97     cmsg = CMSG_FIRSTHDR (&hdr);
  98     cmsg->cmsg_level = SOL_SOCKET;
  99     cmsg->cmsg_type = SCM_RIGHTS;
 100     cmsg->cmsg_len = CMSG_LEN (sizeof (fd));
 101     memcpy (CMSG_DATA (cmsg), &fd, sizeof (fd));
 102     hdr.msg_controllen = cmsg->cmsg_len;
 103
 104     return sendmsg(p, &hdr, MSG_NOSIGNAL) == sizeof (val) ? 0 : -1;
 105 }
 106
 107
 108 /**
 109  * Background process run as root to open privileged TCP ports.
 110  */
 111 static void rootprocess (int fd)
 112 {
 113     union
 114     {
 115         struct sockaddr         sa;
 116         struct sockaddr_storage ss;
 117         struct sockaddr_in      sin;
 118 #ifdef AF_INET6
 119         struct sockaddr_in6     sin6;
 120 #endif
 121     } addr;
 122
 123     while (recv (fd, &addr.ss, sizeof (addr.ss), 0) == sizeof (addr.ss))
 124     {
 125         unsigned len;
 126         int sock;
 127         int family;
 128
 129         switch (addr.sa.sa_family)
 130         {
 131             case AF_INET:
 132                 if (!is_allowed_port (addr.sin.sin_port))
 133                 {
 134                     if (send_err (fd, EACCES))
 135                         return;
 136                     continue;
 137                 }
 138                 len = sizeof (struct sockaddr_in);
 139                 family = PF_INET;
 140                 break;
 141
 142 #ifdef AF_INET6
 143             case AF_INET6:
 144                 if (!is_allowed_port (addr.sin6.sin6_port))
 145                 {
 146                     if (send_err (fd, EACCES))
 147                         return;
 148                     continue;
 149                 }
 150                 len = sizeof (struct sockaddr_in6);
 151                 family = PF_INET6;
 152                 break;
 153 #endif
 154
 155             default:
 156                 if (send_err (fd, EAFNOSUPPORT))
 157                     return;
 158                 continue;
 159         }
 160
 161         sock = socket (family, SOCK_STREAM, IPPROTO_TCP);
 162         if (sock != -1)
 163         {
 164             const int val = 1;
 165
 166             setsockopt (sock, SOL_SOCKET, SO_REUSEADDR, &val, sizeof (val));
 167 #ifdef AF_INET6
 168             if (addr.sa.sa_family == AF_INET6)
 169                 setsockopt (sock, IPPROTO_IPV6, IPV6_V6ONLY, &val, sizeof (val));
 170 #endif
 171             if (bind (sock, &addr.sa, len) == 0)
 172             {
 173                 send_fd (fd, sock);
 174                 close (sock);
 175                 continue;
 176             }
 177             close (sock);
 178         }
 179         send_err (fd, errno);
 180     }
 181 }
 182
 183 /* TODO?
 184  *  - use libcap if available,
 185  *  - call chroot
 186  */
 187
 188 int main (int argc, char *argv[])
 189 {
 190     /* Support for dynamically opening RTSP, HTTP and HTTP/SSL ports */
 191     int pair[2];
 192
 193     if (socketpair (AF_LOCAL, SOCK_STREAM, 0, pair))
 194         return 1;
 195     if (pair[0] < 3)
 196         goto error; /* we want 0, 1 and 2 open */
 197
 198 #ifdef SO_NOSIGPIPE
 199     setsockopt(pair[1], SOL_SOCKET, SO_NOSIGPIPE, &(int){ 1 }, sizeof (int));
 200 #endif
 201
 202     pid_t pid = fork ();
 203     switch (pid)
 204     {
 205         case -1:
 206             goto error;
 207
 208         case 0:
 209         {
 210             int null = open ("/dev/null", O_RDWR);
 211             if (null != -1)
 212             {
 213                 dup2 (null, 0);
 214                 dup2 (null, 1);
 215                 dup2 (null, 2);
 216                 close (null);
 217             }
 218             close (pair[0]);
 219             setsid ();
 220             rootprocess (pair[1]);
 221             exit (0);
 222         }
 223     }
 224
 225     close (pair[1]);
 226     pair[1] = -1;
 227
 228     char buf[21];
 229     snprintf (buf, sizeof (buf), "%d", pair[0]);
 230     setenv ("VLC_ROOTWRAP_SOCK", buf, 1);
 231
 232     /* Support for real-time priorities */
 233 #ifdef RLIMIT_RTPRIO
 234     struct rlimit rlim;
 235     rlim.rlim_max = rlim.rlim_cur = sched_get_priority_min (SCHED_RR) + 24;
 236     setrlimit (RLIMIT_RTPRIO, &rlim);
 237 #endif
 238
 239     uid_t uid = getuid ();
 240     if (uid == 0)
 241     {
 242         const char *sudo = getenv ("SUDO_UID");
 243         if (sudo)
 244             uid = atoi (sudo);
 245     }
 246     if (uid == 0)
 247     {
 248         fputs("Cannot determine unprivileged user for VLC!\n", stderr);
 249         exit (1);
 250     }
 251     setuid (uid);
 252
 253     if (!setuid (0)) /* sanity check: we cannot get root back */
 254         exit (1);
 255
 256     /* Yeah, the user can execute just about anything from here.
 257      * But we've dropped privileges, so it does not matter. */
 258     if (strlen (argv[0]) < sizeof ("-wrapper"))
 259         goto error;
 260     argv[0][strlen (argv[0]) - strlen ("-wrapper")] = '\0';
 261
 262     (void)argc;
 263     if (execvp (argv[0], argv))
 264         perror (argv[0]);
 265
 266 error:
 267     close (pair[0]);
 268     if (pair[1] != -1)
 269         close (pair[1]);
 270     return 1;
 271 }