common/nameser/ns_samedomain.c

/*
 * Copyright (c) 2004 by Internet Systems Consortium, Inc. ("ISC")
 * Copyright (c) 1995,1999 by Internet Software Consortium.
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
 * OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#ifndef lint
static const char rcsid[] = "$Id: ns_samedomain.c,v 1.6 2005/04/27 04:56:40 sra Exp $";
#endif

#include "port_before.h"

#include <sys/types.h>
#include <arpa/nameser.h>
#include <errno.h>
#include <string.h>

#include "port_after.h"

/*%
 *  Check whether a name belongs to a domain.
 *
 * Inputs:
 *\li   a - the domain whose ancestory is being verified
 *\li   b - the potential ancestor we're checking against
 *
 * Return:
 *\li   boolean - is a at or below b?
 *
 * Notes:
 *\li   Trailing dots are first removed from name and domain.
 *  Always compare complete subdomains, not only whether the
 *  domain name is the trailing string of the given name.
 *
 *\li   "host.foobar.top" lies in "foobar.top" and in "top" and in ""
 *  but NOT in "bar.top"
 */

int
ns_samedomain(const char *a, const char *b) {
    size_t la, lb;
    int diff, i, escaped;
    const char *cp;

    la = strlen(a);
    lb = strlen(b);

    /* Ignore a trailing label separator (i.e. an unescaped dot) in 'a'. */
    if (la != 0U && a[la - 1] == '.') {
        escaped = 0;
        /* Note this loop doesn't get executed if la==1. */
        for (i = la - 2; i >= 0; i--)
            if (a[i] == '\\') {
                if (escaped)
                    escaped = 0;
                else
                    escaped = 1;
            } else
                break;
        if (!escaped)
            la--;
    }

    /* Ignore a trailing label separator (i.e. an unescaped dot) in 'b'. */
    if (lb != 0U && b[lb - 1] == '.') {
        escaped = 0;
        /* note this loop doesn't get executed if lb==1 */
        for (i = lb - 2; i >= 0; i--)
            if (b[i] == '\\') {
                if (escaped)
                    escaped = 0;
                else
                    escaped = 1;
            } else
                break;
        if (!escaped)
            lb--;
    }

    /* lb == 0 means 'b' is the root domain, so 'a' must be in 'b'. */
    if (lb == 0U)
        return (1);

    /* 'b' longer than 'a' means 'a' can't be in 'b'. */
    if (lb > la)
        return (0);

    /* 'a' and 'b' being equal at this point indicates sameness. */
    if (lb == la)
        return (strncasecmp(a, b, lb) == 0);

    /* Ok, we know la > lb. */

    diff = la - lb;

    /*
     * If 'a' is only 1 character longer than 'b', then it can't be
     * a subdomain of 'b' (because of the need for the '.' label
     * separator).
     */
    if (diff < 2)
        return (0);

    /*
     * If the character before the last 'lb' characters of 'b'
     * isn't '.', then it can't be a match (this lets us avoid
     * having "foobar.com" match "bar.com").
     */
    if (a[diff - 1] != '.')
        return (0);

    /*
     * We're not sure about that '.', however.  It could be escaped
         * and thus not a really a label separator.
     */
    escaped = 0;
    for (i = diff - 2; i >= 0; i--)
        if (a[i] == '\\') {
            if (escaped)
                escaped = 0;
            else
                escaped = 1;
        } else
            break;
    if (escaped)
        return (0);

    /* Now compare aligned trailing substring. */
    cp = a + diff;
    return (strncasecmp(cp, b, lb) == 0);
}

/*%
 *  is "a" a subdomain of "b"?
 */
int
ns_subdomain(const char *a, const char *b) {
    return (ns_samename(a, b) != 1 && ns_samedomain(a, b));
}

/*%
 *  make a canonical copy of domain name "src"
 *
 * notes:
 * \code
 *  foo -> foo.
 *  foo. -> foo.
 *  foo.. -> foo.
 *  foo\. -> foo\..
 *  foo\\. -> foo\\.
 * \endcode
 */

int
ns_makecanon(const char *src, char *dst, size_t dstsize) {
    size_t n = strlen(src);

    if (n + sizeof "." > dstsize) {         /*%< Note: sizeof == 2 */
        errno = EMSGSIZE;
        return (-1);
    }
    strcpy(dst, src);
    while (n >= 1U && dst[n - 1] == '.')        /*%< Ends in "." */
        if (n >= 2U && dst[n - 2] == '\\' &&    /*%< Ends in "\." */
            (n < 3U || dst[n - 3] != '\\')) /*%< But not "\\." */
            break;
        else
            dst[--n] = '\0';
    dst[n++] = '.';
    dst[n] = '\0';
    return (0);
}

/*%
 *  determine whether domain name "a" is the same as domain name "b"
 *
 * return:
 *\li   -1 on error
 *\li   0 if names differ
 *\li   1 if names are the same
 */

int
ns_samename(const char *a, const char *b) {
    char ta[NS_MAXDNAME], tb[NS_MAXDNAME];

    if (ns_makecanon(a, ta, sizeof ta) < 0 ||
        ns_makecanon(b, tb, sizeof tb) < 0)
        return (-1);
    if (strcasecmp(ta, tb) == 0)
        return (1);
    else
        return (0);
}

/*! \file */