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 #if HAVE_CONFIG_H
  22 # include <config.h>
  23 #endif
  24
  25 #include <stdlib.h> /* exit() */
  26 #include <stdio.h>
  27 #include <string.h>
  28
  29 #include <sys/types.h>
  30 #include <unistd.h>
  31 #include <fcntl.h>
  32 #include <sys/stat.h>
  33 #include <sys/socket.h>
  34 #include <sys/uio.h>
  35 #include <sys/resource.h> /* getrlimit() */
  36 #include <sched.h>
  37 #include <errno.h>
  38 #include <netinet/in.h>
  39
  40 #if defined (AF_INET6) && !defined (IPV6_V6ONLY)
  41 # warning Uho, your IPv6 support is broken and has been disabled. Fix your C library.
  42 # undef AF_INET6
  43 #endif
  44
  45 #ifndef AF_LOCAL
  46 # define AF_LOCAL AF_UNIX
  47 #endif
  48 /* Required yet non-standard cmsg functions */
  49 #ifndef CMSG_ALIGN
  50 # define CMSG_ALIGN(len) (((len) + sizeof(intptr_t)-1) & ~(sizeof(intptr_t)-1))
  51 #endif
  52 #ifndef CMSG_SPACE
  53 # define CMSG_SPACE(len) (CMSG_ALIGN(sizeof(struct cmsghdr)) + CMSG_ALIGN(len))
  54 #endif
  55 #ifndef CMSG_LEN
  56 # define CMSG_LEN(len) (CMSG_ALIGN(sizeof(struct cmsghdr)) + (len))
  57 #endif
  58
  59 static inline int is_allowed_port (uint16_t port)
  60 {
  61     port = ntohs (port);
  62     return (port == 80) || (port == 443) || (port == 554);
  63 }
  64
  65
  66 static inline int send_err (int fd, int err)
  67 {
  68     return send (fd, &err, sizeof (err), 0) == sizeof (err) ? 0 : -1;
  69 }
  70
  71 /**
  72  * Send a file descriptor to another process
  73  */
  74 static int send_fd (int p, int fd)
  75 {
  76     struct msghdr hdr;
  77     struct iovec iov;
  78     struct cmsghdr *cmsg;
  79     char buf[CMSG_SPACE (sizeof (fd))];
  80     int val = 0;
  81
  82     hdr.msg_name = NULL;
  83     hdr.msg_namelen = 0;
  84     hdr.msg_iov = &iov;
  85     hdr.msg_iovlen = 1;
  86     hdr.msg_control = buf;
  87     hdr.msg_controllen = sizeof (buf);
  88
  89     iov.iov_base = &val;
  90     iov.iov_len = sizeof (val);
  91
  92     cmsg = CMSG_FIRSTHDR (&hdr);
  93     cmsg->cmsg_level = SOL_SOCKET;
  94     cmsg->cmsg_type = SCM_RIGHTS;
  95     cmsg->cmsg_len = CMSG_LEN (sizeof (fd));
  96     memcpy (CMSG_DATA (cmsg), &fd, sizeof (fd));
  97     hdr.msg_controllen = cmsg->cmsg_len;
  98
  99     return sendmsg (p, &hdr, 0) == sizeof (val) ? 0 : -1;
 100 }
 101
 102
 103 /**
 104  * Background process run as root to open privileged TCP ports.
 105  */
 106 static void rootprocess (int fd)
 107 {
 108     struct sockaddr_storage ss;
 109
 110     while (recv (fd, &ss, sizeof (ss), 0) == sizeof (ss))
 111     {
 112         unsigned len;
 113         int sock;
 114
 115         switch (ss.ss_family)
 116         {
 117             case AF_INET:
 118                 if (!is_allowed_port (((struct sockaddr_in *)&ss)->sin_port))
 119                 {
 120                     if (send_err (fd, EACCES))
 121                         return;
 122                     continue;
 123                 }
 124                 len = sizeof (struct sockaddr_in);
 125                 break;
 126
 127 #ifdef AF_INET6
 128             case AF_INET6:
 129                 if (!is_allowed_port (((struct sockaddr_in6 *)&ss)->sin6_port))
 130                 {
 131                     if (send_err (fd, EACCES))
 132                         return;
 133                     continue;
 134                 }
 135                 len = sizeof (struct sockaddr_in6);
 136                 break;
 137 #endif
 138
 139             default:
 140                 if (send_err (fd, EAFNOSUPPORT))
 141                     return;
 142                 continue;
 143         }
 144
 145         sock = socket (ss.ss_family, SOCK_STREAM, IPPROTO_TCP);
 146         if (sock != -1)
 147         {
 148             const int val = 1;
 149
 150             setsockopt (sock, SOL_SOCKET, SO_REUSEADDR, &val, sizeof (val));
 151 #ifdef AF_INET6
 152             if (ss.ss_family == AF_INET6)
 153                 setsockopt (sock, IPPROTO_IPV6, IPV6_V6ONLY, &val, sizeof (val));
 154 #endif
 155             if (bind (sock, (struct sockaddr *)&ss, len) == 0)
 156             {
 157                 send_fd (fd, sock);
 158                 close (sock);
 159                 continue;
 160             }
 161         }
 162         send_err (fd, errno);
 163     }
 164 }
 165
 166 /* TODO?
 167  *  - use libcap if available,
 168  *  - call chroot
 169  */
 170
 171 int main (int argc, char *argv[])
 172 {
 173     /* Support for dynamically opening RTSP, HTTP and HTTP/SSL ports */
 174     int pair[2];
 175
 176     if (socketpair (AF_LOCAL, SOCK_STREAM, 0, pair))
 177         return 1;
 178     if (pair[0] < 3)
 179         goto error; /* we want 0, 1 and 2 open */
 180
 181     pid_t pid = fork ();
 182     switch (pid)
 183     {
 184         case -1:
 185             goto error;
 186
 187         case 0:
 188         {
 189             int null = open ("/dev/null", O_RDWR);
 190             if (null != -1)
 191             {
 192                 dup2 (null, 0);
 193                 dup2 (null, 1);
 194                 dup2 (null, 2);
 195                 close (null);
 196             }
 197             close (pair[0]);
 198             setsid ();
 199             rootprocess (pair[1]);
 200             exit (0);
 201         }
 202     }
 203
 204     close (pair[1]);
 205     pair[1] = -1;
 206
 207     char buf[21];
 208     snprintf (buf, sizeof (buf), "%d", pair[0]);
 209     setenv ("VLC_ROOTWRAP_SOCK", buf, 1);
 210
 211     /* Support for real-time priorities */
 212 #ifdef RLIMIT_RTPRIO
 213     struct rlimit rlim;
 214     rlim.rlim_max = rlim.rlim_cur = sched_get_priority_min (SCHED_RR) + 24;
 215     setrlimit (RLIMIT_RTPRIO, &rlim);
 216 #endif
 217
 218     uid_t uid = getuid ();
 219     if (uid == 0)
 220     {
 221         const char *sudo = getenv ("SUDO_UID");
 222         if (sudo)
 223             uid = atoi (sudo);
 224     }
 225     if (uid == 0)
 226     {
 227         fprintf (stderr, "Cannot determine unprivileged user for VLC!\n");
 228         exit (1);
 229     }
 230     setuid (uid);
 231
 232     if (!setuid (0)) /* sanity check: we cannot get root back */
 233         exit (1);
 234
 235     /* Yeah, the user can execute just about anything from here.
 236      * But we've dropped privileges, so it does not matter. */
 237     if (strlen (argv[0]) < sizeof ("-wrapper"))
 238         goto error;
 239     argv[0][strlen (argv[0]) - strlen ("-wrapper")] = '\0';
 240
 241     (void)argc;
 242     if (execvp (argv[0], argv))
 243         perror (argv[0]);
 244
 245 error:
 246     close (pair[0]);
 247     if (pair[1] != -1)
 248         close (pair[1]);
 249     return 1;
 250 }