/*
* 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/refcnt.h>
#include <gpxe/xfer.h>
#include <gpxe/open.h>
#include <gpxe/resolv.h>
#include <gpxe/retry.h>
#include <gpxe/tcpip.h>
#include <gpxe/dhcp.h>
#include <gpxe/dns.h>
/** @file
*
* DNS protocol
*
*/
/** The DNS server */
struct sockaddr_tcpip nameserver = {
.st_port = htons ( DNS_PORT ),
};
/** A DNS request */
struct dns_request {
/** Reference counter */
struct refcnt refcnt;
/** Name resolution interface */
struct resolv_interface resolv;
/** Data transfer interface */
struct xfer_interface socket;
/** Retry timer */
struct retry_timer timer;
/** Socket address to fill in with resolved address */
struct sockaddr sa;
/** Current query packet */
struct dns_query query;
/** Location of query info structure within current packet
*
* The query info structure is located immediately after the
* compressed name.
*/
struct dns_query_info *qinfo;
/** Recursion counter */
unsigned int recursion;
};
/**
* 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 data transfer interface */
xfer_nullify ( &dns->socket );
xfer_close ( &dns->socket, rc );
/* Mark name resolution as complete */
resolv_done ( &dns->resolv, &dns->sa, rc );
}
/**
* 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,
const 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,
const 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 ( const 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;
}
/**
* Send next packet in DNS request
*
* @v dns DNS request
*/
static int dns_send_packet ( struct dns_request *dns ) {
static unsigned int qid = 0;
size_t qlen;
/* 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 */
qlen = ( ( ( void * ) dns->qinfo ) - ( ( void * ) &dns->query )
+ sizeof ( dns->qinfo ) );
return xfer_deliver_raw ( &dns->socket, &dns->query, qlen );
}
/**
* 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 socket UDP socket
* @v data DNS reply
* @v len Length of DNS reply
* @ret rc Return status code
*/
static int dns_xfer_deliver_raw ( struct xfer_interface *socket,
const void *data, size_t len ) {
struct dns_request *dns =
container_of ( socket, struct dns_request, socket );
const 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->sa;
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;
}
}
/**
* Receive new data
*
* @v socket UDP socket
* @v rc Reason for close
*/
static void dns_xfer_close ( struct xfer_interface *socket, int rc ) {
struct dns_request *dns =
container_of ( socket, struct dns_request, socket );
if ( ! rc )
rc = -ECONNABORTED;
dns_done ( dns, rc );
}
/** DNS socket operations */
static struct xfer_interface_operations dns_socket_operations = {
.close = dns_xfer_close,
.vredirect = xfer_vopen,
.seek = ignore_xfer_seek,
.window = unlimited_xfer_window,
.alloc_iob = default_xfer_alloc_iob,
.deliver_iob = xfer_deliver_as_raw,
.deliver_raw = dns_xfer_deliver_raw,
};
/**
* Resolve name using DNS
*
* @v resolv Name resolution interface
* @v name Name to resolve
* @v sa Socket address to fill in
* @ret rc Return status code
*/
static int dns_resolv ( struct resolv_interface *resolv,
const char *name, struct sockaddr *sa ) {
struct dns_request *dns;
int rc;
/* Fail immediately if no DNS servers */
if ( ! nameserver.st_family ) {
DBG ( "DNS not attempting to resolve \"%s\": "
"no DNS servers\n", name );
return -ENXIO;
}
/* Allocate DNS structure */
dns = zalloc ( sizeof ( *dns ) );
if ( ! dns )
return -ENOMEM;
resolv_init ( &dns->resolv, &null_resolv_ops, &dns->refcnt );
xfer_init ( &dns->socket, &dns_socket_operations, &dns->refcnt );
dns->timer.expired = dns_timer_expired;
memcpy ( &dns->sa, sa, sizeof ( dns->sa ) );
/* 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 */
if ( ( rc = xfer_open_socket ( &dns->socket, SOCK_DGRAM,
( struct sockaddr * ) &nameserver,
NULL ) ) != 0 ) {
DBGC ( dns, "DNS %p could not open socket: %s\n",
dns, strerror ( rc ) );
goto err;
}
/* Send first DNS packet */
dns_send_packet ( dns );
/* Attach parent interface, mortalise self, and return */
resolv_plug_plug ( &dns->resolv, resolv );
ref_put ( &dns->refcnt );
return 0;
err:
ref_put ( &dns->refcnt );
return rc;
}
/** DNS name resolver */
struct resolver dns_resolver __resolver ( RESOLV_NORMAL ) = {
.name = "DNS",
.resolv = dns_resolv,
};
/**
* Apply DHCP nameserver option
*
* @v tag DHCP option tag
* @v option DHCP option
*/
static int apply_dhcp_nameserver ( unsigned int tag __unused,
struct dhcp_option *option ) {
struct sockaddr_in *sin_nameserver;
sin_nameserver = ( struct sockaddr_in * ) &nameserver;
sin_nameserver->sin_family = AF_INET;
dhcp_ipv4_option ( option, &sin_nameserver->sin_addr );
return 0;
}
/** DHCP nameserver applicator */
struct dhcp_option_applicator dhcp_nameserver_applicator __dhcp_applicator = {
.tag = DHCP_DNS_SERVERS,
.apply = apply_dhcp_nameserver,
};
