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3. Virtuald

3.1 Introduction

Every network connection is made up of two IP address/port pairs. The API (Applications Program Interface) for network programming is called the Sockets API. The socket acts like an open file and by reading/writing to it you can send data over a network connection. There is a function call getsockname that will return the IP address of the local socket. Virtuald uses getsockname to determine which IP on the local machine is being accessed. Virtuald reads a config file to retrieve the directory associated with that IP. It will chroot to that directory and hand the connection off to the service. Chroot resets / or the root directory to a new point so everything higher in the directory tree is cut off from the running program. Therefore, each IP address gets their own virtual filesystem. To the network program this is transparent and the program will behave like nothing happened. Virtuald in conjunction with a program like inetd can then be used to virtualize any service.

3.2 Inetd

Inetd is a network super server that listens at multiple ports and when it receives a connection (for example, an incoming pop request), inetd performs the network negotiation and hands the network connection off to the specified program. This prevents services from running idly when they are not needed.

A standard /etc/inetd.conf file looks like this:

ftp stream tcp nowait root /usr/sbin/tcpd \
        wu.ftpd -l -a
pop-3 stream tcp nowait root /usr/sbin/tcpd \
        in.qpop -s

A virtual /etc/inetd.conf file looks like this:

ftp stream tcp nowait root /usr/local/bin/virtuald \
        virtuald /virtual/conf.ftp wu.ftpd -l -a
pop-3 stream tcp nowait root /usr/local/bin/virtuald \
        virtuald /virtual/conf.pop in.qpop -s

3.3 Config File

Each service gets a config file that will control what IPs and directories are allowed for that service. You can have one master config file or several config files if you want each service to get a different list of domains. A config file looks like this:

# This is a comment and so are blank lines

# Format IP SPACE dir NOSPACES
10.10.10.129 /virtual/domain1.com
10.10.10.130 /virtual/domain2.com
10.10.10.157 /virtual/domain3.com

# Default option for all other IPs
default /

3.4 Source

This is the C source code to the virtuald program. Compile it and install it in /usr/local/bin with permission 0755, user root, and group root. The only compile option is VERBOSELOG which will turn on/off logging of connections.

#include <netinet/in.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <stdarg.h>
#include <unistd.h>
#include <string.h>
#include <syslog.h>
#include <stdio.h>

#undef VERBOSELOG

#define BUFSIZE 8192

int getipaddr(char **ipaddr)
{
        struct sockaddr_in virtual_addr;
        static char ipaddrbuf[BUFSIZE];
        int virtual_len;
        char *ipptr;

        virtual_len=sizeof(virtual_addr);
        if (getsockname(0,(struct sockaddr *)&virtual_addr,&virtual_len)<0)
        {
                syslog(LOG_ERR,"getipaddr: getsockname failed: %m");
                return -1;
        }
        if (!(ipptr=inet_ntoa(virtual_addr.sin_addr)))
        {
                syslog(LOG_ERR,"getipaddr: inet_ntoa failed: %m");
                return -1;
        }
        strncpy(ipaddrbuf,ipptr,sizeof(ipaddrbuf)-1);
        *ipaddr=ipaddrbuf;
        return 0;
}

int iptodir(char **dir,char *ipaddr,char *filename)
{
        char buffer[BUFSIZE],*bufptr;
        static char dirbuf[BUFSIZE];
        FILE *fp;

        if (!(fp=fopen(filename,"r")))
        {
                syslog(LOG_ERR,"iptodir: fopen failed: %m");
                return -1;
        }
        *dir=NULL;
        while(fgets(buffer,BUFSIZE,fp))
        {
                buffer[strlen(buffer)-1]=0;
                if (*buffer=='#' || *buffer==0)
                        continue;
                if (!(bufptr=strchr(buffer,' ')))
                {
                        syslog(LOG_ERR,"iptodir: strchr failed");
                        return -1;
                }
                *bufptr++=0;
                if (!strcmp(buffer,ipaddr))
                {
                        strncpy(dirbuf,bufptr,sizeof(dirbuf)-1);
                        *dir=dirbuf;
                        break;
                }
                if (!strcmp(buffer,"default"))
                {
                        strncpy(dirbuf,bufptr,sizeof(dirbuf)-1);
                        *dir=dirbuf;
                        break;
                }
        }
        if (fclose(fp)==EOF)
        {
                syslog(LOG_ERR,"iptodir: fclose failed: %m");
                return -1;
        }
        if (!*dir)
        {
                syslog(LOG_ERR,"iptodir: ip not found in conf file");
                return -1;
        }
        return 0;
}

int main(int argc,char **argv)
{
        char *ipaddr,*dir;

        openlog("virtuald",LOG_PID,LOG_DAEMON);

#ifdef VERBOSELOG
        syslog(LOG_ERR,"Virtuald Starting: $Revision: 1.49 $");
#endif
        if (!argv[1])
        {
                syslog(LOG_ERR,"invalid arguments: no conf file");
                exit(0);
        }
        if (!argv[2])
        {
                syslog(LOG_ERR,"invalid arguments: no program to run");
                exit(0);
        }
        if (getipaddr(&ipaddr))
        {
                syslog(LOG_ERR,"getipaddr failed");
                exit(0);
        }
#ifdef VERBOSELOG
        syslog(LOG_ERR,"Incoming ip: %s",ipaddr);
#endif
        if (iptodir(&dir,ipaddr,argv[1]))
        {
                syslog(LOG_ERR,"iptodir failed");
                exit(0);
        }
        if (chroot(dir)<0)
        {
                syslog(LOG_ERR,"chroot failed: %m");
                exit(0);
        }
#ifdef VERBOSELOG
        syslog(LOG_ERR,"Chroot dir: %s",dir);
#endif
        if (chdir("/")<0)
        {
                syslog(LOG_ERR,"chdir failed: %m");
                exit(0);
        }
        if (execvp(argv[2],argv+2)<0)
        {
                syslog(LOG_ERR,"execvp failed: %m");
                exit(0);
        }

        closelog();

        exit(0);
}