Implement root wrapper to allow using privileged TCP ports

while not running the whole VLC as root - closes #440

Makefile.am

@@ -446,6 +446,7 @@ SOURCES_libvlc_common = \
 	src/network/tcp.c \
 	src/network/udp.c \
 	src/network/httpd.c \
+	src/network/rootwrap.c \
 	src/network/tls.c \
 	src/misc/charset.c \
 	src/misc/md5.c \

src/network/rootwrap.c

+/*****************************************************************************
+ * rootwrap.c
+ *****************************************************************************
+ * Copyright © 2005 Rémi Denis-Courmont
+ * $Id$
+ *
+ * Author: Rémi Denis-Courmont <rem # videolan.org>
+ *
+ * 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., 59 Temple Place - Suite 330, Boston, MA  02111, USA.
+ *****************************************************************************/
+
+#if HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+#ifdef HAVE_GETEUID
+# define ENABLE_ROOTWRAP 1
+#endif
+
+#ifdef ENABLE_ROOTWRAP
+
+#include <stdlib.h> /* exit() */
+#include <stdio.h>
+
+#include <sys/types.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <sys/socket.h>
+#include <sys/resource.h> /* getrlimit() */
+#include <sys/wait.h>
+#include <sys/un.h>
+#include <pwd.h> /* getpwnam(), getpwuid() */
+#include <grp.h> /* setgroups() */
+#include <errno.h>
+#include <netinet/in.h>
+#include <pthread.h>
+
+/*#ifndef HAVE_CLEARENV
+extern char **environ;
+
+static int clearenv (void)
+{
+    environ = NULL;
+    return 0;
+}
+#endif*/
+
+/**
+ * Converts username to UID.
+ */
+static uid_t parse_user (const char *name)
+{
+    struct passwd *pw;
+
+    pw = getpwnam (name);
+    if (pw == NULL)
+        return 0;
+
+    return pw->pw_uid;
+}
+
+
+/**
+ * Tries to find a real non-root user ID
+ */
+static uid_t guess_user (void)
+{
+    const char *name;
+    uid_t uid;
+
+    /* Try real UID */
+    uid = getuid ();
+    if (uid)
+        return uid;
+
+    /* Try sudo */
+    name = getenv ("SUDO_USER");
+    if (name != NULL)
+    {
+        uid = parse_user (name);
+        if (uid != 0)
+            return uid;
+    }
+
+    /* Try VLC_USER */
+    name = getenv ("VLC_USER");
+    if (name != NULL)
+    {
+        uid = parse_user (name);
+        if (uid != 0)
+            return uid;
+    }
+
+    /* Try vlc */
+    uid = parse_user ("vlc");
+    if (uid != 0)
+        return uid;
+
+    /* Try nobody */
+    uid = parse_user ("nobody");
+    if (uid != 0)
+        return uid;
+
+    return 65534;
+}
+
+
+/**
+ * Returns the main GID associated with a given UID.
+ */
+static gid_t guess_gid (uid_t uid)
+{
+    struct passwd *pw;
+
+    pw = getpwuid (uid);
+    if (pw != NULL)
+        return pw->pw_gid;
+    return 65534;
+}
+
+
+static int is_allowed_port (uint16_t port)
+{
+    port = ntohs (port);
+
+    return (port == 80) || (port == 443) || (port == 554);
+}
+
+
+static int send_err (int fd, int err)
+{
+    return send (fd, &err, sizeof (err), 0) == sizeof (err) ? 0 : -1;
+}
+
+/**
+ * Ugly POSIX(?) code to pass 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, 0) == sizeof (val) ? 0 : -1;
+}
+
+
+/**
+ * Background process run as root to open privileged TCP ports.
+ */
+static void rootprocess (int fd)
+{
+    struct sockaddr_storage ss;
+
+    /* TODO:
+     *  - use libcap if available,
+     *  - call chroot
+     */
+    while (recv (fd, &ss, sizeof (ss), 0) == sizeof (ss))
+    {
+        unsigned len;
+        int sock;
+
+        switch (ss.ss_family)
+        {
+            case AF_INET:
+                if (!is_allowed_port (((struct sockaddr_in *)&ss)->sin_port))
+                {
+                    if (send_err (fd, EACCES))
+                        return;
+                    continue;
+                }
+                len = sizeof (struct sockaddr_in);
+                break;
+
+#ifdef AF_INET6
+            case AF_INET6:
+                if (!is_allowed_port (((struct sockaddr_in6 *)&ss)->sin6_port))
+                {
+                    if (send_err (fd, EACCES))
+                        return;
+                    continue;
+                }
+                len = sizeof (struct sockaddr_in6);
+                break;
+#endif
+
+            default:
+                if (send_err (fd, EAFNOSUPPORT))
+                    return;
+                continue;
+        }
+
+        sock = socket (ss.ss_family, SOCK_STREAM, IPPROTO_TCP);
+        if (sock != -1)
+        {
+            const int val = 1;
+
+            setsockopt (sock, SOL_SOCKET, SO_REUSEADDR, &val, sizeof (val));
+            if (ss.ss_family == AF_INET6)
+                setsockopt (sock, SOL_IPV6, IPV6_V6ONLY, &val, sizeof (val));
+
+            if (bind (sock, (struct sockaddr *)&ss, len) == 0)
+            {
+                send_fd (fd, sock);
+                close (sock);
+                continue;
+            }
+        }
+        send_err (fd, errno);
+    }
+}
+
+static int rootwrap_sock = -1;
+static pid_t rootwrap_pid = -1;
+
+static void close_rootwrap (void)
+{
+    close (rootwrap_sock);
+    waitpid (rootwrap_pid, NULL, 0);
+}
+
+void rootwrap (void)
+{
+    struct rlimit lim;
+    int fd, pair[2];
+    uid_t u;
+    gid_t g;
+
+    u = geteuid ();
+    /* Are we running with root privileges? */
+    if (u != 0)
+    {
+        setuid (u);
+        return;
+    }
+
+    /* Make sure 0, 1 and 2 are opened, and only these. */
+    if (getrlimit (RLIMIT_NOFILE, &lim))
+        exit (1);
+
+    for (fd = 3; ((unsigned)fd) < lim.rlim_cur; fd++)
+        close (fd);
+
+    fd = dup (2);
+    if (fd <= 2)
+        exit (1);
+    close (fd);
+
+    fputs ("Starting VLC root wrapper...", stderr);
+
+    u = guess_user ();
+    fprintf (stderr, " using UID %u", (unsigned)u);
+
+    g = guess_gid (u);
+    fprintf (stderr, ", using GID %u\n", (unsigned)g);
+
+    /* GID */
+    setgid (g);
+    setgroups (0, NULL);
+
+    if (socketpair (AF_LOCAL, SOCK_STREAM, 0, pair))
+    {
+        perror ("socketpair");
+        goto nofork;
+    }
+
+    switch (rootwrap_pid = fork ())
+    {
+        case -1:
+            perror ("fork");
+            close (pair[0]);
+            close (pair[1]);
+            break;
+
+        case 0:
+            close (0);
+            close (1);
+            close (2);
+            close (pair[0]);
+            rootprocess (pair[1]);
+            exit (0);
+
+        default:
+            close (pair[1]);
+            rootwrap_sock = pair[0];
+            break;
+    }
+
+nofork:
+    /* UID */
+    setuid (u);
+
+    atexit (close_rootwrap);
+}
+
+
+/**
+ * Ugly POSIX(?) code to receive a file descriptor from another process
+ */
+static int recv_fd (int p)
+{
+    struct msghdr hdr;
+    struct iovec iov;
+    struct cmsghdr *cmsg;
+    int val, fd;
+    char buf[CMSG_SPACE (sizeof (fd))];
+
+    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);
+
+    if (recvmsg (p, &hdr, 0) != sizeof (val))
+        return -1;
+
+    for (cmsg = CMSG_FIRSTHDR (&hdr); cmsg != NULL;
+         cmsg = CMSG_NXTHDR (&hdr, cmsg))
+    {
+        if ((cmsg->cmsg_level == SOL_SOCKET)
+         && (cmsg->cmsg_type = SCM_RIGHTS)
+         && (cmsg->cmsg_len >= CMSG_LEN (sizeof (fd))))
+        {
+            memcpy (&fd, CMSG_DATA (cmsg), sizeof (fd));
+            return fd;
+        }
+    }
+
+    return -1;
+}
+
+/**
+ * Tries to obtain a bound TCP socket from the root process
+ */
+int rootwrap_bind (int family, int socktype, int protocol,
+                   const struct sockaddr *addr, size_t alen)
+{
+    /* can't use libvlc */
+    static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
+
+    struct sockaddr_storage ss;
+    int fd;
+
+    if (rootwrap_sock == -1)
+    {
+        errno = EACCES;
+        return -1;
+    }
+
+    switch (family)
+    {
+        case AF_INET:
+            if (alen < sizeof (struct sockaddr_in))
+            {
+                errno = EINVAL;
+                return -1;
+            }
+            break;
+
+#ifdef AF_INET6
+        case AF_INET6:
+            if (alen < sizeof (struct sockaddr_in6))
+            {
+                errno = EINVAL;
+                return -1;
+            }
+            break;
+#endif
+
+        default:
+            errno = EAFNOSUPPORT;
+            return -1;
+    }
+
+    if (family != addr->sa_family)
+    {
+        errno = EAFNOSUPPORT;
+        return -1;
+    }
+
+    /* Only TCP is implemented at the moment */
+    if ((socktype != SOCK_STREAM)
+     || (protocol && (protocol != IPPROTO_TCP)))
+    {
+        errno = EACCES;
+        return -1;
+    }
+
+    memset (&ss, 0, sizeof (ss));
+    memcpy (&ss, addr, alen > sizeof (ss) ? sizeof (ss) : alen);
+
+    pthread_mutex_lock (&mutex);
+    if (send (rootwrap_sock, &ss, sizeof (ss), 0) != sizeof (ss))
+        return -1;
+
+    fd = recv_fd (rootwrap_sock);
+    pthread_mutex_unlock (&mutex);
+
+    if (fd != -1)
+    {
+        int val;
+
+        val = fcntl (fd, F_GETFL, 0);
+        fcntl (fd, F_SETFL, ((val != -1) ? val : 0) | O_NONBLOCK);
+    }
+
+    return fd;
+}
+
+#else
+# include <stddef.h>
+
+struct sockaddr;
+
+void rootwrap (void)
+{
+}
+
+int rootwrap_bind (int family, int socktype, int protocol,
+                   const struct sockaddr *addr, size_t alen)
+{
+    return -1;
+}
+
+#endif /* ENABLE_ROOTWRAP */

src/network/tcp.c

@@ -50,6 +50,8 @@ static int SocksHandshakeTCP( vlc_object_t *,
                               const char *psz_host, int i_port );
 extern int net_Socket( vlc_object_t *p_this, int i_family, int i_socktype,
                        int i_protocol );
+extern int rootwrap_bind (int family, int socktype, int protocol,
+                          const struct sockaddr *addr, size_t alen);
 
 /*****************************************************************************
  * __net_ConnectTCP:
@@ -302,13 +304,30 @@ int *__net_ListenTCP( vlc_object_t *p_this, const char *psz_host, int i_port )
         {
 #if defined(WIN32) || defined(UNDER_CE)
             msg_Warn( p_this, "cannot bind socket (%i)", WSAGetLastError( ) );
+            net_Close( fd );
+            continue;
 #else
-            msg_Warn( p_this, "cannot bind socket (%s)", strerror( errno ) );
-#endif
+            int saved_errno;
+
+            saved_errno = errno;
             net_Close( fd );
+            fd = rootwrap_bind( ptr->ai_family, ptr->ai_socktype,
+                                ptr->ai_protocol, ptr->ai_addr,
+                                ptr->ai_addrlen );
+            if( fd != -1 )
+            {
+                msg_Dbg( p_this, "got socket %d from rootwrap", fd );
+            }
+            else
+            {
+                msg_Warn( p_this, "cannot bind socket (%s)",
+                          strerror( saved_errno ) );
                 continue;
             }
+#endif
+        }
 
+        msg_Dbg( p_this, "using socket %d from rootwrap", fd );
         /* Listen */
         if( listen( fd, 100 ) == -1 )
         {

src/vlc.c

@@ -45,6 +45,8 @@
 static void SigHandler  ( int i_signal );
 #endif
 
+extern void rootwrap( void );
+
 /*****************************************************************************
  * main: parse command line, start interface and spawn threads.
  *****************************************************************************/
@@ -73,6 +75,8 @@ int main( int i_argc, char *ppsz_argv[] )
     }
 #endif
 
+    rootwrap ();
+    
     /* Create a libvlc structure */
     i_ret = VLC_Create();
     if( i_ret < 0 )