lib/libresolv/res_gethost.c

/*
 * Copyright 2015 Gary Mills
 * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

/*
 * Copyright (c) 1985, 1988 Regents of the University of California.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms are permitted
 * provided that this notice is preserved and that due credit is given
 * to the University of California at Berkeley. The name of the University
 * may not be used to endorse or promote products derived from this
 * software without specific prior written permission. This software
 * is provided ``as is'' without express or implied warranty.
 *
 */

#include <sys/param.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <ctype.h>
#include <netdb.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <arpa/inet.h>
#include <arpa/nameser.h>
#include <resolv.h>
#include <syslog.h>
#include "crossl.h"

/*
 * When the name service switch calls libresolv, it doesn't want fallback
 * to /etc/hosts, so we provide a method to turn it off.
 */
static int  no_hosts_fallback = 0;

void
__res_set_no_hosts_fallback(void) {
    no_hosts_fallback = 1;
}

static int
__res_no_hosts_fallback(void) {
    return(no_hosts_fallback);
}

static char *h_addr_ptrs[MAXADDRS + 1];

static struct hostent host;
static char *host_aliases[MAXALIASES];
static char hostbuf[BUFSIZ+1];
static struct in_addr host_addr;
static char HOSTDB[] = "/etc/hosts";
static FILE *hostf = NULL;
static char hostaddr[MAXADDRS];
static char *host_addrs[2];
static int stayopen = 0;
static char *any();

#if PACKETSZ > 1024
#define MAXPACKET   PACKETSZ
#else
#define MAXPACKET   1024
#endif

typedef union {
    HEADER hdr;
    u_char buf[MAXPACKET];
} querybuf;

static union {
    long al;
    char ac;
} align;


int h_errno;

static struct hostent *
getanswer(answer, anslen, iquery)
    querybuf *answer;
    int anslen;
    int iquery;
{
    register HEADER *hp;
    register u_char *cp;
    register int n;
    u_char *eom;
    char *bp, **ap;
    int type, class, buflen, ancount, qdcount;
    int haveanswer, getclass = C_ANY;
    char **hap;

    eom = answer->buf + anslen;
    /*
     * find first satisfactory answer
     */
    hp = &answer->hdr;
    ancount = ntohs(hp->ancount);
    qdcount = ntohs(hp->qdcount);
    bp = hostbuf;
    buflen = sizeof (hostbuf);
    cp = answer->buf + sizeof (HEADER);
    if (qdcount) {
        if (iquery) {
            if ((n = dn_expand(answer->buf, eom,
                cp, (u_char *)bp, buflen)) < 0) {
                h_errno = NO_RECOVERY;
                return ((struct hostent *) NULL);
            }
            cp += n + QFIXEDSZ;
            host.h_name = bp;
            n = strlen(bp) + 1;
            bp += n;
            buflen -= n;
        } else
            cp += dn_skipname(cp, eom) + QFIXEDSZ;
        while (--qdcount > 0)
            cp += dn_skipname(cp, eom) + QFIXEDSZ;
    } else if (iquery) {
        if (hp->aa)
            h_errno = HOST_NOT_FOUND;
        else
            h_errno = TRY_AGAIN;
        return ((struct hostent *) NULL);
    }
    ap = host_aliases;
    host.h_aliases = host_aliases;
    hap = h_addr_ptrs;
#if BSD >= 43 || defined(h_addr)    /* new-style hostent structure */
    host.h_addr_list = h_addr_ptrs;
#endif
    haveanswer = 0;
    while (--ancount >= 0 && cp < eom && haveanswer < MAXADDRS) {
        if ((n = dn_expand(answer->buf, eom,
            cp, (u_char *)bp, buflen)) < 0)
            break;
        cp += n;
        type = _getshort(cp);
        cp += sizeof (u_short);
        class = _getshort(cp);
        cp += sizeof (u_short) + sizeof (u_long);
        n = _getshort(cp);
        cp += sizeof (u_short);
        if (type == T_CNAME) {
            cp += n;
            if (ap >= &host_aliases[MAXALIASES-1])
                continue;
            *ap++ = bp;
            n = strlen(bp) + 1;
            bp += n;
            buflen -= n;
            continue;
        }
        if (iquery && type == T_PTR) {
            if ((n = dn_expand(answer->buf, eom,
                cp, (u_char *)bp, buflen)) < 0) {
                cp += n;
                continue;
            }
            cp += n;
            host.h_name = bp;
            return (&host);
        }
        if (iquery || type != T_A) {
#ifdef DEBUG
            if (_res.options & RES_DEBUG)
                printf("unexpected answer type %d, size %d\n",
                    type, n);
#endif
            cp += n;
            continue;
        }
        if (haveanswer) {
            if (n != host.h_length) {
                cp += n;
                continue;
            }
            if (class != getclass) {
                cp += n;
                continue;
            }
        } else {
            host.h_length = n;
            getclass = class;
            host.h_addrtype = (class == C_IN) ? AF_INET : AF_UNSPEC;
            if (!iquery) {
                host.h_name = bp;
                bp += strlen(bp) + 1;
            }
        }

        bp += sizeof (align) - ((u_long)bp % sizeof (align));

        if (bp + n >= &hostbuf[sizeof (hostbuf)]) {
#ifdef DEBUG
            if (_res.options & RES_DEBUG)
                printf("size (%d) too big\n", n);
#endif
            break;
        }
#ifdef SYSV
        memcpy((void *)(*hap++ = bp), (void *)cp, n);
#else
        bcopy(cp, *hap++ = bp, n);
#endif
        bp += n;
        cp += n;
        haveanswer++;
    }
    if (haveanswer) {
        *ap = NULL;
#if BSD >= 43 || defined(h_addr)    /* new-style hostent structure */
        *hap = NULL;
#else
        host.h_addr = h_addr_ptrs[0];
#endif
        return (&host);
    } else {
        h_errno = TRY_AGAIN;
        return ((struct hostent *) NULL);
    }
}

static struct hostent *_gethtbyname();

struct hostent *
res_gethostbyname(name)
    char *name;
{
    querybuf buf;
    register char *cp;
    int n;

    /*
     * disallow names consisting only of digits/dots, unless
     * they end in a dot.
     */
    if (isdigit(name[0]))
        for (cp = name; /*EMPTY*/; ++cp) {
            if (!*cp) {
                if (*--cp == '.')
                    break;
                h_errno = HOST_NOT_FOUND;
                return ((struct hostent *) NULL);
            }
            if (!isdigit(*cp) && *cp != '.')
                break;
        }

    if ((n = res_search(name, C_IN, T_A, buf.buf, sizeof (buf))) < 0) {
#ifdef DEBUG
        if (_res.options & RES_DEBUG)
            printf("res_search failed\n");
#endif
        if (errno == ECONNREFUSED)
            return (_gethtbyname(name));
        else
            return ((struct hostent *) NULL);
    }
    return (getanswer(&buf, n, 0));
}

static struct hostent *_gethtbyaddr();

static struct hostent *
_getrhbyaddr(addr, len, type)
    char *addr;
    int len, type;
{
    int n;
    querybuf buf;
    register struct hostent *hp;
    char qbuf[MAXDNAME];

    if (type != AF_INET)
        return ((struct hostent *) NULL);
    (void) sprintf(qbuf, "%d.%d.%d.%d.in-addr.arpa",
        ((unsigned)addr[3] & 0xff),
        ((unsigned)addr[2] & 0xff),
        ((unsigned)addr[1] & 0xff),
        ((unsigned)addr[0] & 0xff));
    n = res_query(qbuf, C_IN, T_PTR, (u_char *)&buf, sizeof (buf));
    if (n < 0) {
#ifdef DEBUG
        if (_res.options & RES_DEBUG)
            printf("res_query failed\n");
#endif
        if (errno == ECONNREFUSED)
            return (_gethtbyaddr(addr, len, type));
        return ((struct hostent *) NULL);
    }
    hp = getanswer(&buf, n, 1);
    if (hp == NULL)
        return ((struct hostent *) NULL);
    hp->h_addrtype = type;
    hp->h_length = len;
    h_addr_ptrs[0] = (char *)&host_addr;
    h_addr_ptrs[1] = (char *)0;
    host_addr = *(struct in_addr *)addr;
    return (hp);
}

/*
 * First we get what the PTR record says, but do an extra call
 * to gethostbyname() to make sure that someone is not trying to
 * spoof us.  Hopefully this is not done that often, so good
 * performance is not really an issue.
 */
struct hostent *
res_gethostbyaddr(addr, len, type)
    char    *addr;
    int len;
    int type;
{
    char        **a, hbuf[MAXHOSTNAMELEN];
    struct hostent  *hp, *hp2;

    if ((hp = _getrhbyaddr(addr, len, type)) == (struct hostent *)NULL)
        return ((struct hostent *)NULL);

    /* hang on to what we got as an answer */
    (void) strcpy(hbuf, hp->h_name);

    /* check to make sure by doing a forward query */
    if ((hp2 = res_gethostbyname(hbuf)) != (struct hostent *)NULL)
        for (a = hp2->h_addr_list; *a; a++)
#ifdef SYSV
            if (memcmp(*a, addr, hp2->h_length) == 0)
#else
            if (bcmp(*a, addr, hp2->h_length) == 0)
#endif
                return (hp2);

    /*
     * we've been spoofed, make sure to log it.
     * XXX - syslog needs a security priority level.
     */
    syslog(LOG_NOTICE, "gethostbyaddr: %s != %s", hbuf,
        inet_ntoa(*(struct in_addr *)addr));
    return ((struct hostent *)NULL);
}

static void
_sethtent(int f)
{
    if (__res_no_hosts_fallback()) return;

    if (hostf == NULL)
        hostf = fopen(HOSTDB, "r");
    else
        rewind(hostf);
    stayopen |= f;
}

static void
_endhtent(void)
{
    if (__res_no_hosts_fallback()) return;

    if (hostf && !stayopen) {
        (void) fclose(hostf);
        hostf = NULL;
    }
}

static struct hostent *
_gethtent()
{
    char *p;
    register char *cp, **q;

    if (__res_no_hosts_fallback()) return(NULL);

    if (hostf == NULL && (hostf = fopen(HOSTDB, "r")) == NULL)
        return (NULL);
again:
    if ((p = fgets(hostbuf, BUFSIZ, hostf)) == NULL)
        return (NULL);
    if (*p == '#')
        goto again;
    cp = any(p, "#\n");
    if (cp == NULL)
        goto again;
    *cp = '\0';
    cp = any(p, " \t");
    if (cp == NULL)
        goto again;
    *cp++ = '\0';
    /* THIS STUFF IS INTERNET SPECIFIC */
#if BSD >= 43 || defined(h_addr)    /* new-style hostent structure */
    host.h_addr_list = host_addrs;
#endif
    host.h_addr = hostaddr;
    *((u_long *)host.h_addr) = inet_addr(p);
    host.h_length = sizeof (u_long);
    host.h_addrtype = AF_INET;
    while (*cp == ' ' || *cp == '\t')
        cp++;
    host.h_name = cp;
    q = host.h_aliases = host_aliases;
    cp = any(cp, " \t");
    if (cp != NULL)
        *cp++ = '\0';
    while (cp && *cp) {
        if (*cp == ' ' || *cp == '\t') {
            cp++;
            continue;
        }
        if (q < &host_aliases[MAXALIASES - 1])
            *q++ = cp;
        cp = any(cp, " \t");
        if (cp != NULL)
            *cp++ = '\0';
    }
    *q = NULL;
    return (&host);
}

static char *
any(cp, match)
    register char *cp;
    char *match;
{
    register char *mp, c;

    while (c = *cp) {
        for (mp = match; *mp; mp++)
            if (*mp == c)
                return (cp);
        cp++;
    }
    return ((char *)0);
}

static struct hostent *
_gethtbyname(name)
    char *name;
{
    register struct hostent *p;
    register char **cp;

    _sethtent(0);
    while (p = _gethtent()) {
        if (strcasecmp(p->h_name, name) == 0)
            break;
        for (cp = p->h_aliases; *cp != 0; cp++)
            if (strcasecmp(*cp, name) == 0)
                goto found;
    }
found:
    _endhtent();
    return (p);
}

static struct hostent *
_gethtbyaddr(addr, len, type)
    char *addr;
    int len, type;
{
    register struct hostent *p;

    _sethtent(0);
    while (p = _gethtent())
#ifdef SYSV
        if (p->h_addrtype == type && !memcmp(p->h_addr, addr, len))
#else
        if (p->h_addrtype == type && !bcmp(p->h_addr, addr, len))
#endif
            break;
    _endhtent();
    return (p);
}