diff options
| -rw-r--r-- | src/dnsserver.c | 242 |
1 files changed, 242 insertions, 0 deletions
diff --git a/src/dnsserver.c b/src/dnsserver.c new file mode 100644 index 0000000..e06ecb1 --- /dev/null +++ b/src/dnsserver.c @@ -0,0 +1,242 @@ +/* $Id: dnsserver.c,v 1.1 2002-05-23 04:40:42 rjkaes Exp $ + * + * This is a DNS resolver program. I've borrowed _liberally_ from + * Squid's dnsserver program. Only one argument is passed to this + * program (the path to the Unix socket.) Additionally, this program + * will be started by tinyproxy itself. + * + * As noted, communication is conducted over a Unix socket. The + * client opens a connection and writes a '\n' terminated string with + * either a domain name (if an address is required) or a + * dotted-decimal IP address (if the domain name is required.) This + * program will then respond with a '\n' terminated string starting + * with either "$addr" if IP addresses are being returned, or "$name" + * if a host name is returned. The connection will remain open until + * the "$shutdown" command is sent by the client. + * + * Copyright (C) 2002 Robert James Kaes (rjkaes@flarenet.com) + * + * This program is free software; you can redistribute it and/or modify it + * under the terms of the GNU General Public License as published by the + * Free Software Foundation; either version 2, or (at your option) any + * later version. + * + * This program is distributed in the hope that it will be useful, but + * WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + * General Public License for more details. + */ + +#include "common.h" + +#include "daemon.h" +#include "heap.h" +#include "network.h" +#include "text.h" + +/* + * Store a copy of the location of the Unix socket + */ +static char *unix_socket_path; + +/* + * Handle SIGCHLD signals so that zombies are reaped. + */ +static void +child_signal_handler(int signo) +{ + pid_t pid; + int status; + + while ((pid = waitpid(-1, &status, WNOHANG)) > 0) + ; + return; +} + +/* + * Handle the SIGTERM signal to remove the Unix socket + */ +static void +term_signal_handler(int signo) +{ + unlink(unix_socket_path); + return; +} + +/* + * Text error messages for DNS problems. + */ +static char* +dns_error_messages(int err) +{ + if (err == HOST_NOT_FOUND) + return "Host not found (authoritative)"; + else if (err == TRY_AGAIN) + return "Host not found (non-authoritative)"; + else if (err == NO_RECOVERY) + return "Non recoverable errors"; + else if (err == NO_DATA || err == NO_ADDRESS) + return "Valid name, no data record of requested type"; + else + return "Unknown DNS problem"; +} + +/* + * Lookup and return the information for a host name (or IP address) + */ +static int +lookup_dns(int fd) +{ + const struct hostent *result = NULL; + int reverse_lookup = 0; + int retry = 0; + int i; + struct in_addr addr; + char *buf; + ssize_t len; + char address_buf[1024]; + + len = readline(fd, &buf); + chomp(buf, len); + + if (strcmp(buf, "$shutdown") == 0) + return 0; + if (strcmp(buf, "$hello") == 0) { + write_message(fd, "$alive\n"); + return 1; + } + + /* + * Check to see if the buffer is an IP address in dotted-decimal + * form. + */ + for (;;) { + if (inet_aton(buf, &addr)) { + reverse_lookup = 1; + result = gethostbyaddr((char *)&addr.s_addr, 4, AF_INET); + } else { + result = gethostbyname(buf); + } + + if (NULL != result) + break; + if (h_errno != TRY_AGAIN) + break; + if (++retry == 3) + break; + sleep(1); + } + + if (NULL == result) { + if (h_errno == TRY_AGAIN) { + write_message(fd, "$fail Name Server for domain '%s' is unavailable.\n", buf); + } else { + write_message(fd, "$fail DNS Domain '%s' is invalid: %s.\n", + buf, dns_error_messages(h_errno)); + } + return 1; + } + + if (reverse_lookup) { + write_message(fd, "$name %s\n", result->h_name); + return 1; + } + + strlcpy(address_buf, "$addr", sizeof(address_buf)); + for (i = 0; i < 32; i++) { + if (!result->h_addr_list[i]) + break; + + memcpy(&addr, result->h_addr_list[i], sizeof(addr)); + + strlcat(address_buf, " ", sizeof(address_buf)); + strlcat(address_buf, inet_ntoa(addr), sizeof(address_buf)); + } + write_message(fd, "%s\n", address_buf); + + return 1; +} + +/* + * Print out a usage message. + */ +static void +usage(void) +{ + fprintf(stderr, "usage: dnsserver path\n"); +} + +/* + * Start up function. Create the sockets and fork() when needed. + */ +int +main(int argc, char **argv) +{ + int listenfd, connfd; + pid_t childpid; + socklen_t clilen; + struct sockaddr_un cliaddr, servaddr; + + if (--argc != 1) { + usage(); + exit(1); + } + + /* + * The path for the socket is supplied as the one (and only) command + * line argument. + */ + unix_socket_path = safestrdup(argv[1]); + if (!unix_socket_path) { + fprintf(stderr, "%s: could not allocate memory.\n", argv[0]); + exit(1); + } + + /* Create the listening socket */ + listenfd = socket(AF_LOCAL, SOCK_STREAM, 0); + if (listenfd < 0) { + fprintf(stderr, "%s: could not create listening socket.\n", + argv[0]); + exit(1); + } + + memset(&servaddr, 0, sizeof(servaddr)); + servaddr.sun_family = AF_LOCAL; + strcpy(servaddr.sun_path, unix_socket_path); + + if (bind(listenfd, (struct sockaddr *)&servaddr, sizeof(servaddr)) < 0) { + fprintf(stderr, "%s: could not bind socket.\n", argv[0]); + exit(1); + } + if (listen(listenfd, MAXLISTEN) < 0) { + fprintf(stderr, "%s: could not start listening on socket.\n", + argv[0]); + exit(1); + } + + set_signal_handler(SIGCHLD, child_signal_handler); + set_signal_handler(SIGTERM, term_signal_handler); + + for ( ; ; ) { + clilen = sizeof(cliaddr); + if ((connfd = accept(listenfd, (struct sockaddr *)&cliaddr, &clilen)) < 0) { + if (errno == EINTR) + continue; + else + exit(1); + } + + if ((childpid = fork()) == 0) { + /* child process */ + close(listenfd); + + while (lookup_dns(connfd)) + ; + + close(connfd); + exit(0); + } + + close(connfd); /* parent closes connected socket */ + } +} |