/*
 * 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);
}