source: umon/main/common/dns.c

/**************************************************************************
 *
 * Copyright (c) 2013 Alcatel-Lucent
 *
 * Alcatel Lucent licenses this file to You under the Apache License,
 * Version 2.0 (the "License"); you may not use this file except in
 * compliance with the License.  A copy of the License is contained the
 * file LICENSE at the top level of this repository.
 * You may also obtain a copy of the License at:
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 **************************************************************************
 *
 * dns.c:
 *
 * This file implements a basic DNS client and some form of a multicast-DNS
 * reponder.  The functionality provides the basic ability to retrieve an IP
 * address from a domain name.
 * Refer to RFC 1035 section 4.1 for the packet format.
 *
 *
 * Original author:     Ed Sutter (ed.sutter@alcatel-lucent.com)
 *
 */
#include "config.h"
#if INCLUDE_DNS
#include "endian.h"
#include "genlib.h"
#include "stddefs.h"
#include "ether.h"
#include "cli.h"
#include "timer.h"

const char mDNSIp[] = { 224, 0, 0, 251 };
const char mDNSMac[] = { 0x01, 0x00, 0x5e, 0x00, 0x00, 0xfb };

char *dnsErrStr(int errno);

short DnsPort;
static unsigned short dnsId;
static unsigned long dnsIP;
static char dnsErrno, dnsWaiting, dnsCacheInitialized;
static struct dnscache hostnames[MAX_CACHED_HOSTNAMES];

/* ip_to_bin...
 * Essentially identical to IpToBin() in ethernet.c, but without
 * the error message.
 */
int
ip_to_bin(char *ascii,uchar *binary)
{
    int i, digit;
    char    *acpy;

    acpy = ascii;
    for(i=0; i<4; i++) {
        digit = (int)strtol(acpy,&acpy,10);
        if(((i != 3) && (*acpy++ != '.')) ||
                ((i == 3) && (*acpy != 0)) ||
                (digit < 0) || (digit > 255)) {
            return(-1);
        }
        binary[i] = (uchar)digit;
    }
    return(0);
}


/* getHostAddr():
 * This function is a simplified version of gethostbyname().
 * Given a domain name, this function will first query a
 * locally maintained cache then, if not found there, it will
 * issue a DNS query to retrieve the hosts IP address.
 */
unsigned long
getHostAddr(char *hostname)
{
    short   port;
    struct ip *ipp;
    struct Udphdr *udpp;
    struct dnshdr *dnsp;
    struct elapsed_tmr tmr;
    struct ether_header *enetp;
    uchar   binenet[8], *enetaddr;
    unsigned long   srvrip, binip;
    char    *pp, *np, *srvrname, *dot;
    int     i, namelen, pktsize, ip_len;

    /* First check to see if the incoming host name is simply a
     * decimal-dot-formatted IP address.  If it is, then just
     * convert it to a 32-bit long and return here...
     */
    if(ip_to_bin(hostname,(uchar *)&binip) == 0) {
        return(binip);
    }

    if(!dnsCacheInitialized) {
        dnsCacheInit();
    }

    dnsErrno = DNSERR_NULL;

    /* First try to find the hostname in our local cache...
     */
    for(i=0; i<MAX_CACHED_HOSTNAMES; i++) {
        if(strcmp(hostnames[i].name,hostname) == 0) {
            return(hostnames[i].addr);
        }
    }

    /* If not in the cache, we query the network.  First look
     * for a DNSSRVR defined in the environment.  If found, use
     * it; else, use IP broadcast.
     */

    /* See if this is a mDNS request...
     */
    if(strstr(hostname,".local")) {
        DnsPort = port = DNSMCAST_PORT;
        srvrip = htonl(DNSMCAST_IP);
        memcpy((char *)binenet,(char *)mDNSMac,sizeof(mDNSMac));
        enetaddr = binenet;
    } else {
        port = IPPORT_DNS;
        DnsPort = port+1;
        srvrname = getenv("DNSSRVR");
        if(srvrname == (char *)0) {
            srvrip = 0xffffffff;
        } else {
            if(IpToBin(srvrname,(uchar *)&srvrip) < 0) {
                return(0);
            }
        }

        /* Get the ethernet address for the IP:
         */
        enetaddr = ArpEther((uchar *)&srvrip,binenet,0);
        if(!enetaddr) {
            printf("ARP failed for 0x%x\n",srvrip);
            return(0);
        }
    }

    /* Retrieve an ethernet buffer from the driver and populate the
     * ethernet level of packet:
     */
    enetp = (struct ether_header *) getXmitBuffer();
    memcpy((char *)&enetp->ether_shost,(char *)BinEnetAddr,6);
    memcpy((char *)&enetp->ether_dhost,(char *)binenet,6);
    enetp->ether_type = htons(ETHERTYPE_IP);

    /* Move to the IP portion of the packet and populate it
     * appropriately:
     */
    ipp = (struct ip *)(enetp + 1);
    ipp->ip_vhl = IP_HDR_VER_LEN;
    ipp->ip_tos = 0;
    ipp->ip_id = ipId();
    ipp->ip_off = 0;
    ipp->ip_ttl = UDP_TTL;
    ipp->ip_p = IP_UDP;
    memcpy((char *)&ipp->ip_src.s_addr,(char *)BinIpAddr,4);
    memcpy((char *)&ipp->ip_dst.s_addr,(char *)&srvrip,4);

    /* Now UDP...
     */
    udpp = (struct Udphdr *)(ipp + 1);
    udpp->uh_sport = htons(DnsPort);
    udpp->uh_dport = htons(port);

    /* Finally, the DNS data ...
     */
    dnsp = (struct dnshdr *)(udpp+1);

    /* Build the message.  This query supports a single internet
     * host-address question.
     *
     * Fixed header...
     */
    dnsId = ipId();
    dnsp->id = htons(dnsId);        /* Unique id */
    dnsp->param = 0;                /* Parameter field */
    dnsp->num_questions = htons(1); /* # of questions */
    dnsp->num_answers = 0;          /* # of answers */
    dnsp->num_authority = 0;        /* # of authority */
    dnsp->num_additional = 0;       /* # of additional */

    /* The formatted name list..
     * Each name is preceded by a single-byte length, so for our
     * query, the list is "LNNNLNNNLNNN0", where...
     *  'L' is the single-byte length of the name.
     *  'NN..N' is variable-lenght domain.
     *  '0' is the length of the next name in the list; hence,
     *      indicating the end of the list.
     *
     * For each '.' (dot)  in the hostname, there is a
     * LNNN pair.
     */
    pp = (char *)dnsp->question;
    np = (char *)hostname;
    namelen = strlen(hostname);
    do {
        dot = strchr(np,'.');
        if(dot) {
            *pp++ = dot-np;
            memcpy(pp,np,dot-np);
            pp += (dot-np);
            np = dot + 1;
        } else {
            *pp++ = strlen(np);
            strcpy(pp,np);
        }
    } while(dot);


    /* Since the size of the name can be arbitrary (not aligned),
     * we must populate the TYPE and CLASS fields one byte at
     * a time...
     */
    pp += (strlen(np) + 1);
    *pp++ = 0;
    *pp++ = 1;  /* type = 'A' (host address) */
    *pp++ = 0;
    *pp = 1;    /* class = 'IN' (the internet) */

    /* Send the DNS query:
     * Total message size is...
     * FIXED_HDR_SIZE + NAME_SIZE + TYPE_SIZE + CLASS_SIZE + (NAMELEN_SIZE*2)
     * where...
     *  FIXED_HDR_SIZE  = 12
     *  NAME_SIZE       = strlen(hostname) = namelen
     *  TYPE_SIZE       = sizeof(short) = 2
     *  CLASS_SIZE      = sizeof(short) = 2
     *  NAMELEN_SIZE    = sizeof(char) = 1
     *
     * There are 2 name lengths.  The first one is the size of the host
     * name we are querying for and the second one is zero (indicating no
     * more names in the list).
     * So, the total length of the packet is <namelen + 18>.
     */

    pktsize = namelen+18;
    ip_len = sizeof(struct ip) + sizeof(struct Udphdr) + pktsize;
    ipp->ip_len = htons(ip_len);
    udpp->uh_ulen = htons((ushort)(ip_len - sizeof(struct ip)));

    ipChksum(ipp);          /* Compute csum of ip hdr */
    udpChksum(ipp);         /* Compute UDP checksum */

//  printf("Sending DNS rqst id=%04x (%d %d)\n",dnsId,pktsize,ip_len);

    dnsWaiting = 1;
    sendBuffer(ETHERSIZE + IPSIZE + UDPSIZE + pktsize);

    /* Wait for 3 seconds for a response...
     */
    startElapsedTimer(&tmr,3000);
    while(!msecElapsed(&tmr)) {
        if(dnsErrno != DNSERR_NULL) {
            break;
        }
        pollethernet();
    }
    if(dnsErrno == DNSERR_COMPLETE) {
        dnsCacheAdd(hostname,dnsIP);
        shell_sprintf("DNSIP","%d.%d.%d.%d",
                      IP1(dnsIP),IP2(dnsIP),IP3(dnsIP), IP4(dnsIP));
        return(dnsIP);
    } else {
        if(dnsErrno == DNSERR_NULL) {
            printf("DNS attempt timeout\n");
        } else {
            printf("DNSErr: %s\n",dnsErrStr((int)dnsErrno));
        }
        setenv("DNSIP",0);
    }
    return(0);
}

/* Note two different processDNS/processMCASTDNS functions...
 * processDNS() provides the necessary code to deal with responses
 * that we should expect to get as a result of issuing a dns request.
 * processMCASTDNS() provides the necessary code to deal with requests
 * from other machines querying for our hostname/ip info.
 */

/* processDNS():
 * This function provides the recieving half of the DNS query above.
 */
int
processDNS(struct ether_header *ehdr,ushort size)
{
    int     i;
    char    *pp;
    struct  ip *ihdr;
    struct  Udphdr *uhdr;
    struct  dnshdr *dhdr;
    unsigned short  rtype, qtot, atot;

    if(dnsWaiting == 0) {
        return(0);
    }

    dnsWaiting = 0;
    ihdr = (struct ip *)(ehdr + 1);
    uhdr = (struct Udphdr *)((char *)ihdr + IP_HLEN(ihdr));
    dhdr = (struct dnshdr *)(uhdr + 1);

//  printf("DNS: (%d)\n",size);
//  printf("  dnsid: %04x\n",htons(dhdr->id));
//  printf("  param: %04x\n",htons(dhdr->param));
//  printf("  quest: %04x\n",htons(dhdr->num_questions));
//  printf("  answe: %04x\n",htons(dhdr->num_answers));
//  printf("  autho: %04x\n",htons(dhdr->num_authority));
//  printf("  addit: %04x\n",htons(dhdr->num_additional));
//  printMem(dhdr->question, size - UDPSIZE - IPSIZE - ETHERSIZE - 12,1);

    /* Verify the DNS response...
     */
    if((htons(dhdr->param) & 0x8000) == 0) {            /* response? */
        dnsErrno = DNSERR_NOTARESPONSE;
        return(0);
    }
    if(htons(dhdr->id) != dnsId) {                      /* correct id? */
        dnsErrno = DNSERR_BADRESPID;
        return(0);
    }
    if((rtype = (htons(dhdr->param) & 0xf)) != 0) {     /* response normal? */
        switch(rtype) {
        case 1:
            dnsErrno = DNSERR_FORMATERR;
            break;
        case 2:
            dnsErrno = DNSERR_SRVRFAILURE;
            break;
        case 3:
            dnsErrno = DNSERR_NAMENOEXIST;
            break;
        default:
            dnsErrno = DNSERR_BADRESPTYPE;
            break;
        }
        return(0);
    }
    qtot = htons(dhdr->num_questions);
    if((atot = htons(dhdr->num_answers)) < 1) {     /* answer count >= 1? */
        dnsErrno = DNSERR_BADANSWRCOUNT;
        return(0);
    }

    /* At this point we can assume that the received packet format
     * is ok.  Now we need to parse the packet for the "answer" to
     * our query...
     */

    /* Set 'pp' to point to the start of the question list.
     * There should only be one question in the response.
     */
    pp = (char *)&dhdr->question;

    /* Skip over the questions:
     */
    for(i=0; i<qtot; i++) {
        while(*pp) {        /* while 'L' is nonzero */
            pp += (*pp + 1);
        }
        pp += 5;            /* Account for last 'L' plus TYPE/CLASS */
    }

    /* The 'pp' pointer is now pointing a list of resource records that
     * correspond to the answer list.  It is from this list that we
     * must retrieve the information we are looking for...
     */

    for(i=0; i<atot; i++) {
        unsigned short type, len;

        /* The first portion of the record is the resource domain name
         * and it may be literal string (a 1-octet count followed by
         * characters that make up the name) or a pointer to a literal
         * string.
         */
        if((*pp & 0xc0) == 0xc0) {  /* compressed? (section 4.1.4 RFC1035) */
            pp += 2;
        } else {
            while(*pp) {            /* while 'L' is nonzero */
                pp += (*pp + 1);
            }
            pp += 1;
        }
        memcpy((char *)&type,pp,2);
        type = htons(type);
        pp += 8;
        memcpy((char *)&len,pp,2);
        len = htons(len);
        if((type == TYPE_A) && (len == 4)) {
            pp += 2;
            memcpy((char *)&dnsIP,pp,4);
            dnsIP = htonl(dnsIP);
        } else {
            pp += (len+2);
        }
    }
    dnsErrno = DNSERR_COMPLETE;
    return(0);
}

/* processMCASTDNS():
 * If we're here, then we've received a request over the Multi-cast
 * DNS address for some host name.  If the hostname in this request
 * matches this board's hostname, then return this board's IP address.
 * If the shell variable HOSTNAME isn't set, then just return immediately.
 */
int
processMCASTDNS(struct ether_header *ehdr,ushort size)
{
    int     l1, ql = 0;
    struct  ip *ihdr;
    char    *pp, *myname;
    struct  Udphdr *uhdr;
    struct  dnshdr *dhdr;

    ihdr = (struct ip *)(ehdr + 1);
    uhdr = (struct Udphdr *)(ihdr + 1);
    dhdr = (struct dnshdr *)(uhdr + 1);

    // If this message is DNS response, branch to processDNS()...
    if((htons(dhdr->param) & 0x8000) == 0x8000) {
        processDNS(ehdr,size);
        return(0);
    }

    if((myname = getenv("HOSTNAME")) == 0) {
        return(0);
    }

    // If this isn't a normal query type, return...
    if((htons(dhdr->param) & 0xf) != 0) {
        return(0);
    }

    // If there isn't exactly 1 question, return...
    if(htons(dhdr->num_questions) != 1) {
        return(0);
    }

    /* At this point we can assume that the received packet format
     * is ok.  Now we need to parse the packet for the "question"...
     */

    /* Set 'pp' to point to the start of the question list.
     */
    pp = (char *)dhdr->question;
    l1 = *pp;
    while(*pp) {
        ql += *pp;
        ql++;
        pp += (*pp + 1);
    }

    /* If the name in the question matches our hostname, then send a
     * reply...
     *
     * Referring to top of pg 20 of the document
     *  http://files.multicastdns.org/draft-cheshire-dnsext-multicastdns.txt...
     *
     * Multicast DNS responses MUST be sent to UDP port 5353 on the
     * 224.0.0.251 multicast address.
     */
    if((l1 == strlen(myname)) &&
            (memcmp(myname,(char *)&dhdr->question[1],l1) == 0)) {
        struct ip *ti, *ri;
        struct Udphdr *tu, *ru;
        struct ether_header *te;
        struct  dnshdr *td;
        short   type, class;
        long    ttl;
        struct  elapsed_tmr tmr;

        te = EtherCopy(ehdr);
        ti = (struct ip *)(te + 1);
        ri = (struct ip *)(ehdr + 1);
        ti->ip_vhl = ri->ip_vhl;
        ti->ip_tos = ri->ip_tos;
        ti->ip_id = ri->ip_id;
        ti->ip_off = ri->ip_off;
        ti->ip_ttl = UDP_TTL;
        ti->ip_p = IP_UDP;
        memcpy((char *)&(ti->ip_src.s_addr),(char *)BinIpAddr,
               sizeof(struct in_addr));
        memcpy((char *)&(ti->ip_dst.s_addr),(char *)mDNSIp,
               sizeof(struct in_addr));

        tu = (struct Udphdr *)(ti + 1);
        ru = (struct Udphdr *)(ri + 1);
        tu->uh_sport = ru->uh_dport;
        tu->uh_dport = htons(DNSMCAST_PORT);

        td = (struct dnshdr *)(tu+1);

        /* Flags: */
        td->id = dhdr->id;
        td->param = htons(0x8400);
        td->num_questions = 0;
        td->num_answers = htons(1);
        td->num_authority = 0;
        td->num_additional = 0;

        /* Answers: */
        pp = (char *)td->question;
        memcpy(pp,(char *)dhdr->question,ql+1);
        pp += (ql+1);

        type = htons(TYPE_A);
        memcpy(pp,(char *)&type,2);
        pp += 2;

        class = htons(CLASS_IN);
        memcpy(pp,(char *)&class,2);
        pp += 2;

        ttl = htonl(900);
        memcpy(pp,(char *)&ttl,4);
        pp += 4;

        *pp++ = 0;  /* 2-byte length of address */
        *pp++ = 4;
        memcpy(pp,(char *)BinIpAddr,4);

        tu->uh_ulen = ecs((UDPSIZE + 27 + ql));
        ti->ip_len = ecs((UDPSIZE + 27 + ql + sizeof(struct ip)));

        ipChksum(ti);       /* Compute checksum of ip hdr */
        udpChksum(ti);      /* Compute UDP checksum */

        /* Delay for some random time between 20-120msec...
         */
        startElapsedTimer(&tmr,20 + (BinEnetAddr[5] & 0x3f));
        while(!msecElapsed(&tmr));

        sendBuffer(ETHERSIZE + IPSIZE + UDPSIZE + 27 + ql);
    }
    return(0);
}

/* DNS Cache utilities:
 */
void
dnsCacheInit(void)
{
    int i;

    for(i=0; i<MAX_CACHED_HOSTNAMES; i++) {
        hostnames[i].idx = 0;
        hostnames[i].addr = 0;
        hostnames[i].name[0] = 0;
    }
    dnsCacheInitialized = 1;
}

int
dnsCacheDump(void)
{
    int i, tot;
    struct  dnscache *hnp;

    tot = 0;
    hnp = hostnames;
    for(i=0; i<MAX_CACHED_HOSTNAMES; i++,hnp++) {
        if(hnp->addr) {
            printf("%3d %30s: %d.%d.%d.%d\n",hnp->idx,hnp->name, IP1(hnp->addr),
                   IP2(hnp->addr), IP3(hnp->addr), IP4(hnp->addr));
            tot++;
        }
    }
    return(tot);
}

int
dnsCacheAdd(char *name, unsigned long inaddr)
{
    int i, li, lowest;
    struct  dnscache *hnp;
    static  int idx = 0;

    if(!dnsCacheInitialized) {
        dnsCacheInit();
    }

    /* Validate incoming name size:
     */
    if((strlen(name) >= MAX_HOSTNAME_SIZE) || (inaddr == 0)) {
        return(-1);
    }

    lowest = 0x70000000;

    /* First look for an empty slot...
     */
    hnp = hostnames;
    li = MAX_CACHED_HOSTNAMES;
    for(i=0; i<MAX_CACHED_HOSTNAMES; i++,hnp++) {
        if(hnp->addr == 0) {
            strcpy(hnp->name,name);
            hnp->addr = inaddr;
            hnp->idx = idx++;
            return(1);
        } else {
            if(hnp->idx < lowest) {
                lowest = hnp->idx;
                li = i;
            }
        }
    }

    if(i == MAX_CACHED_HOSTNAMES) {
        return(-1);
    }

    /* If all slots are filled, use the slot that had the
     * the lowest idx value (this would be the oldest entry)...
     */
    hnp = &hostnames[li];
    strcpy(hnp->name,name);
    hnp->addr = inaddr;
    hnp->idx = idx++;
    return(1);
}

int
dnsCacheDelAddr(unsigned long addr)
{
    int i;

    if(!dnsCacheInitialized) {
        dnsCacheInit();
        return(0);
    }

    for(i=0; i<MAX_CACHED_HOSTNAMES; i++) {
        if(hostnames[i].addr == addr) {
            hostnames[i].name[0] = 0;
            hostnames[i].addr = 0;
            return(1);
        }
    }
    return(0);
}

int
dnsCacheDelName(char *name)
{
    int i;

    if(!dnsCacheInitialized) {
        dnsCacheInit();
        return(0);
    }

    for(i=0; i<MAX_CACHED_HOSTNAMES; i++) {
        if(strcmp(hostnames[i].name,name) == 0) {
            hostnames[i].name[0] = 0;
            hostnames[i].addr = 0;
            return(1);
        }
    }
    return(0);
}

struct dnserr dnsErrTbl[] = {
    { DNSERR_NOSRVR,            "no dns server" },
    { DNSERR_SOCKETFAIL,        "socket fail" },
    { DNSERR_FORMATERR,         "format error" },
    { DNSERR_SRVRFAILURE,       "server error" },
    { DNSERR_NAMENOEXIST,       "no name exists" },
    { DNSERR_BADRESPTYPE,       "bad dns server response" },
    { DNSERR_BADQSTNCOUNT,      "bad question count" },
    { DNSERR_BADANSWRCOUNT,     "bad answer count" },
    { DNSERR_NOTARESPONSE,      "replay not a dns response" },
    { DNSERR_BADRESPID,         "bad dns response id" },

    /* Must be last entry in table: */
    { DNSERR_NULL,              "no error" }
};

char *
dnsErrStr(int errno)
{
    struct  dnserr *dep;

    dep = dnsErrTbl;
    while(dep->errno != DNSERR_NULL) {
        if(dep->errno == errno) {
            return(dep->errstr);
        }
        dep++;
    }
    return("invalid dns errno");
}

char *DnsHelp[] = {
    "DNS Client",
    "{hostname} | {cmd args}",
    " Valid cmd values:",
    "  add   {name} {ip}",
    "  cache {dump | init}",
    "  mdns {on | off}",
    "  del   {name}",
    0,
};

int
DnsCmd(int argc, char *argv[])
{
    unsigned long addr;

    if(argc == 2) {
        if((addr = getHostAddr(argv[1])) != 0) {
            printf("%s: %d.%d.%d.%d\n",argv[1],
                   IP1(dnsIP),IP2(dnsIP),IP3(dnsIP), IP4(dnsIP));
        }
    } else if(argc == 3) {
        if(strcmp(argv[1],"cache") == 0) {
            if(strcmp(argv[2],"dump") == 0) {
                dnsCacheDump();
            } else if(strcmp(argv[2],"init") == 0) {
                dnsCacheInit();
            } else {
                return(CMD_PARAM_ERROR);
            }
        } else if(strcmp(argv[1],"mdns") == 0) {
            extern void enableMulticastReception(void);
            extern void disableMulticastReception(void);

            if(strcmp(argv[2],"on") == 0) {
                enableMulticastReception();
            } else if(strcmp(argv[2],"off") == 0) {
                disableMulticastReception();
            } else {
                return(CMD_PARAM_ERROR);
            }
        } else if(strcmp(argv[1],"del") == 0) {
            dnsCacheDelName(argv[2]);
        } else {
            return(CMD_PARAM_ERROR);
        }
    } else if(argc == 4) {
        if(strcmp(argv[1],"add") == 0) {
            if(IpToBin(argv[3],(uchar *)&addr) < 0) {
                return(CMD_FAILURE);
            }
            dnsCacheAdd(argv[2],addr);
        } else {
            return(CMD_PARAM_ERROR);
        }
    } else {
        return(CMD_PARAM_ERROR);
    }

    return(CMD_SUCCESS);
}

#endif