A working DNS resolver (not yet tied in to anything)

1 files changed, 463 insertions, 0 deletions

diff --git a/src/net/udp/dns.c b/src/net/udp/dns.c
new file mode 100644
index 000000000..17075d68e
--- /dev/null
+++ b/src/net/udp/dns.c
@@ -0,0 +1,463 @@
+/*
+ * Copyright (C) 2006 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * Portions copyright (C) 2004 Anselm M. Hoffmeister
+ * <stockholm@users.sourceforge.net>.
+ *
+ * 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 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., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+#include <byteswap.h>
+#include <gpxe/async.h>
+#include <gpxe/udp.h>
+#include <gpxe/dhcp.h>
+#include <gpxe/dns.h>
+
+/** @file
+ *
+ * DNS protocol
+ *
+ */
+
+/**
+ * Compare DNS reply name against the query name from the original request
+ *
+ * @v dns		DNS request
+ * @v reply		DNS reply
+ * @v rname		Reply name
+ * @ret	zero		Names match
+ * @ret non-zero	Names do not match
+ */
+static int dns_name_cmp ( struct dns_request *dns, struct dns_header *reply, 
+			  const char *rname ) {
+	const char *qname = dns->query.payload;
+	int i;
+
+	while ( 1 ) {
+		/* Obtain next section of rname */
+		while ( ( *rname ) & 0xc0 ) {			
+			rname = ( ( ( char * ) reply ) +
+				  ( ntohs( *((uint16_t *)rname) ) & ~0xc000 ));
+		}
+		/* Check that lengths match */
+		if ( *rname != *qname )
+			return -1;
+		/* If length is zero, we have reached the end */
+		if ( ! *qname )
+			return 0;
+		/* Check that data matches */
+		for ( i = *qname + 1; i > 0 ; i-- ) {
+			if ( *(rname++) != *(qname++) )
+				return -1;
+		}
+	}
+}
+
+/**
+ * Skip over a (possibly compressed) DNS name
+ *
+ * @v name		DNS name
+ * @ret name		Next DNS name
+ */
+static const char * dns_skip_name ( const char *name ) {
+	while ( 1 ) {
+		if ( ! *name ) {
+			/* End of name */
+			return ( name + 1);
+		}
+		if ( *name & 0xc0 ) {
+			/* Start of a compressed name */
+			return ( name + 2 );
+		}
+		/* Uncompressed name portion */
+		name += *name + 1;
+	}
+}
+
+/**
+ * Find an RR in a reply packet corresponding to our query
+ *
+ * @v dns		DNS request
+ * @v reply		DNS reply
+ * @ret rr		DNS RR, or NULL if not found
+ */
+static union dns_rr_info * dns_find_rr ( struct dns_request *dns,
+					 struct dns_header *reply ) {
+	int i, cmp;
+	const char *p = ( ( char * ) reply ) + sizeof ( struct dns_header );
+	union dns_rr_info *rr_info;
+
+	/* Skip over the questions section */
+	for ( i = ntohs ( reply->qdcount ) ; i > 0 ; i-- ) {
+		p = dns_skip_name ( p ) + sizeof ( struct dns_query_info );
+	}
+
+	/* Process the answers section */
+	for ( i = ntohs ( reply->ancount ) ; i > 0 ; i-- ) {
+		cmp = dns_name_cmp ( dns, reply, p );
+		p = dns_skip_name ( p );
+		rr_info = ( ( union dns_rr_info * ) p );
+		if ( cmp == 0 )
+			return rr_info;
+		p += ( sizeof ( rr_info->common ) +
+		       ntohs ( rr_info->common.rdlength ) );
+	}
+
+	return NULL;
+}
+
+/**
+ * Convert a standard NUL-terminated string to a DNS name
+ *
+ * @v string		Name as a NUL-terminated string
+ * @v buf		Buffer in which to place DNS name
+ * @ret next		Byte following constructed DNS name
+ *
+ * DNS names consist of "<length>element" pairs.
+ */
+static char * dns_make_name ( const char *string, char *buf ) {
+	char *length_byte = buf++;
+	char c;
+
+	while ( ( c = *(string++) ) ) {
+		if ( c == '.' ) {
+			*length_byte = buf - length_byte - 1;
+			length_byte = buf;
+		}
+		*(buf++) = c;
+	}
+	*length_byte = buf - length_byte - 1;
+	*(buf++) = '\0';
+	return buf;
+}
+
+/**
+ * Convert an uncompressed DNS name to a NUL-terminated string
+ *
+ * @v name		DNS name
+ * @ret string		NUL-terminated string
+ *
+ * Produce a printable version of a DNS name.  Used only for debugging.
+ */
+static inline char * dns_unmake_name ( char *name ) {
+	char *p;
+	unsigned int len;
+
+	p = name;
+	while ( ( len = *p ) ) {
+		*(p++) = '.';
+		p += len;
+	}
+
+	return name + 1;
+}
+
+/**
+ * Decompress a DNS name
+ *
+ * @v reply		DNS replay
+ * @v name		DNS name
+ * @v buf		Buffer into which to decompress DNS name
+ * @ret next		Byte following decompressed DNS name
+ */
+static char * dns_decompress_name ( struct dns_header *reply,
+				    const char *name, char *buf ) {
+	int i, len;
+
+	do {
+		/* Obtain next section of name */
+		while ( ( *name ) & 0xc0 ) {
+			name = ( ( char * ) reply +
+				 ( ntohs ( *((uint16_t *)name) ) & ~0xc000 ) );
+		}
+		/* Copy data */
+		len = *name;
+		for ( i = len + 1 ; i > 0 ; i-- ) {
+			*(buf++) = *(name++);
+		}
+	} while ( len );
+	return buf;
+}
+
+/**
+ * Mark DNS request as complete
+ *
+ * @v dns		DNS request
+ * @v rc		Return status code
+ */
+static void dns_done ( struct dns_request *dns, int rc ) {
+
+	/* Stop the retry timer */
+	stop_timer ( &dns->timer );
+
+	/* Close UDP connection */
+	udp_close ( &dns->udp );
+
+	/* Mark async operation as complete */
+	async_done ( &dns->async, rc );
+}
+
+/**
+ * Send next packet in DNS request
+ *
+ * @v dns		DNS request
+ */
+static void dns_send_packet ( struct dns_request *dns ) {
+	static unsigned int qid = 0;
+
+	/* Increment query ID */
+	dns->query.dns.id = htons ( ++qid );
+
+	DBGC ( dns, "DNS %p sending query ID %d\n", dns, qid );
+
+	/* Start retransmission timer */
+	start_timer ( &dns->timer );
+
+	/* Send the data */
+	udp_send ( &dns->udp, &dns->query,
+		   ( ( ( void * ) dns->qinfo ) - ( ( void * ) &dns->query )
+		     + sizeof ( dns->qinfo ) ) );
+}
+
+/**
+ * Handle DNS retransmission timer expiry
+ *
+ * @v timer		Retry timer
+ * @v fail		Failure indicator
+ */
+static void dns_timer_expired ( struct retry_timer *timer, int fail ) {
+	struct dns_request *dns =
+		container_of ( timer, struct dns_request, timer );
+
+	if ( fail ) {
+		dns_done ( dns, -ETIMEDOUT );
+	} else {
+		dns_send_packet ( dns );
+	}
+}
+
+/**
+ * Receive new data
+ *
+ * @v udp		UDP connection
+ * @v data		Received data
+ * @v len		Length of received data
+ * @v st_src		Partially-filled source address
+ * @v st_dest		Partially-filled destination address
+ */
+static int dns_newdata ( struct udp_connection *conn, void *data, size_t len,
+			 struct sockaddr_tcpip *st_src __unused,
+			 struct sockaddr_tcpip *st_dest __unused ) {
+	struct dns_request *dns =
+		container_of ( conn, struct dns_request, udp );
+	struct dns_header *reply = data;
+	union dns_rr_info *rr_info;
+	struct sockaddr_in *sin;
+	unsigned int qtype = dns->qinfo->qtype;
+
+	/* Sanity check */
+	if ( len < sizeof ( *reply ) ) {
+		DBGC ( dns, "DNS %p received underlength packet length %zd\n",
+		       dns, len );
+		return -EINVAL;
+	}
+
+	/* Check reply ID matches query ID */
+	if ( reply->id != dns->query.dns.id ) {
+		DBGC ( dns, "DNS %p received unexpected reply ID %d "
+		       "(wanted %d)\n", dns, ntohs ( reply->id ),
+		       ntohs ( dns->query.dns.id ) );
+		return -EINVAL;
+	}
+
+	DBGC ( dns, "DNS %p received reply ID %d\n", dns, ntohs ( reply->id ));
+
+	/* Stop the retry timer.  After this point, each code path
+	 * must either restart the timer by calling dns_send_packet(),
+	 * or mark the DNS operation as complete by calling
+	 * dns_done()
+	 */
+	stop_timer ( &dns->timer );
+
+	/* Search through response for useful answers.  Do this
+	 * multiple times, to take advantage of useful nameservers
+	 * which send us e.g. the CNAME *and* the A record for the
+	 * pointed-to name.
+	 */
+	while ( ( rr_info = dns_find_rr ( dns, reply ) ) ) {
+		switch ( rr_info->common.type ) {
+
+		case htons ( DNS_TYPE_A ):
+
+			/* Found the target A record */
+			DBGC ( dns, "DNS %p found address %s\n",
+			       dns, inet_ntoa ( rr_info->a.in_addr ) );
+			sin = ( struct sockaddr_in * ) dns->st;
+			sin->sin_family = AF_INET;
+			sin->sin_addr = rr_info->a.in_addr;
+
+			/* Mark operation as complete */
+			dns_done ( dns, 0 );
+			return 0;
+
+		case htons ( DNS_TYPE_CNAME ):
+
+			/* Found a CNAME record; update query and recurse */
+			DBGC ( dns, "DNS %p found CNAME\n", dns );
+			dns->qinfo = ( void * ) dns_decompress_name ( reply,
+							 rr_info->cname.cname,
+							 dns->query.payload );
+			dns->qinfo->qtype = htons ( DNS_TYPE_A );
+			dns->qinfo->qclass = htons ( DNS_CLASS_IN );
+			
+			/* Terminate the operation if we recurse too far */
+			if ( ++dns->recursion > DNS_MAX_CNAME_RECURSION ) {
+				DBGC ( dns, "DNS %p recursion exceeded\n",
+				       dns );
+				dns_done ( dns, -ELOOP );
+				return 0;
+			}
+			break;
+
+		default:
+			DBGC ( dns, "DNS %p got unknown record type %d\n",
+			       dns, ntohs ( rr_info->common.type ) );
+			break;
+		}
+	}
+	
+	/* Determine what to do next based on the type of query we
+	 * issued and the reponse we received
+	 */
+	switch ( qtype ) {
+
+	case htons ( DNS_TYPE_A ):
+		/* We asked for an A record and got nothing;
+		 * try the CNAME.
+		 */
+		DBGC ( dns, "DNS %p found no A record; trying CNAME\n", dns );
+		dns->qinfo->qtype = htons ( DNS_TYPE_CNAME );
+		dns_send_packet ( dns );
+		return 0;
+
+	case htons ( DNS_TYPE_CNAME ):
+		/* We asked for a CNAME record.  If we got a response
+		 * (i.e. if the next A query is already set up), then
+		 * issue it, otherwise abort.
+		 */
+		if ( dns->qinfo->qtype == htons ( DNS_TYPE_A ) ) {
+			dns_send_packet ( dns );
+			return 0;
+		} else {
+			DBGC ( dns, "DNS %p found no CNAME record\n", dns );
+			dns_done ( dns, -ENXIO );
+			return 0;
+		}
+
+	default:
+		assert ( 0 );
+		dns_done ( dns, -EINVAL );
+		return 0;
+	}
+}
+
+/** DNS UDP operations */
+struct udp_operations dns_udp_operations = {
+	.newdata = dns_newdata,
+};
+
+/**
+ * Reap asynchronous operation
+ *
+ * @v async		Asynchronous operation
+ */
+static void dns_reap ( struct async *async ) {
+	struct dns_request *dns =
+		container_of ( async, struct dns_request, async );
+
+	free ( dns );
+}
+
+/** DNS asynchronous operations */
+static struct async_operations dns_async_operations = {
+	.reap = dns_reap,
+};
+
+/**
+ * Resolve name using DNS
+ *
+ */
+int dns_resolv ( const char *name, struct sockaddr_tcpip *st,
+		 struct async *parent ) {
+	struct dns_request *dns;
+	union {
+		struct sockaddr_tcpip st;
+		struct sockaddr_in sin;
+	} nameserver;
+	int rc;
+
+	/* Allocate DNS structure */
+	dns = malloc ( sizeof ( *dns ) );
+	if ( ! dns ) {
+		rc = -ENOMEM;
+		goto err;
+	}
+	memset ( dns, 0, sizeof ( *dns ) );
+	dns->st = st;
+	dns->timer.expired = dns_timer_expired;
+	dns->udp.udp_op = &dns_udp_operations;
+
+	/* Create query */
+	dns->query.dns.flags = htons ( DNS_FLAG_QUERY | DNS_FLAG_OPCODE_QUERY |
+				       DNS_FLAG_RD );
+	dns->query.dns.qdcount = htons ( 1 );
+	dns->qinfo = ( void * ) dns_make_name ( name, dns->query.payload );
+	dns->qinfo->qtype = htons ( DNS_TYPE_A );
+	dns->qinfo->qclass = htons ( DNS_CLASS_IN );
+
+	/* Open UDP connection */
+	memset ( &nameserver, 0, sizeof ( nameserver ) );
+	nameserver.sin.sin_family = AF_INET;
+	nameserver.sin.sin_port = htons ( DNS_PORT );
+#warning "DHCP-DNS hack"
+	struct dhcp_option *option =
+		find_global_dhcp_option ( DHCP_DNS_SERVERS );
+	if ( ! option ) {
+		DBGC ( dns, "DNS %p no name servers\n", dns );
+		rc = -ENXIO;
+		goto err;
+	}
+	dhcp_ipv4_option ( option, &nameserver.sin.sin_addr );
+	DBGC ( dns, "DNS %p using nameserver %s\n", dns, 
+	       inet_ntoa ( nameserver.sin.sin_addr ) );
+	udp_connect ( &dns->udp, &nameserver.st );
+	if ( ( rc = udp_open ( &dns->udp, 0 ) ) != 0 )
+		goto err;
+
+	dns_send_packet ( dns );
+
+	async_init ( &dns->async, &dns_async_operations, parent );
+	return 0;	
+
+ err:
+	DBGC ( dns, "DNS %p could not create request: %s\n", 
+	       dns, strerror ( rc ) );
+	free ( dns );
+	return rc;
+}