resolv/ns_samedomain.c

   1 /*
   2  * Copyright (c) 2004 by Internet Systems Consortium, Inc. ("ISC")
   3  * Copyright (c) 1995,1999 by Internet Software Consortium.
   4  *
   5  * Permission to use, copy, modify, and distribute this software for any
   6  * purpose with or without fee is hereby granted, provided that the above
   7  * copyright notice and this permission notice appear in all copies.
   8  *
   9  * THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SOFTWARE CONSORTIUM DISCLAIMS
  10  * ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES
  11  * OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL INTERNET SOFTWARE
  12  * CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
  13  * DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
  14  * PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
  15  * ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
  16  * SOFTWARE.
  17  */
  18
  19 #include <sys/types.h>
  20 #include <arpa/nameser.h>
  21 #include <errno.h>
  22 #include <string.h>
  23
  24 /*%
  25  *      Check whether a name belongs to a domain.
  26  *
  27  * Inputs:
  28  *\li   a - the domain whose ancestry is being verified
  29  *\li   b - the potential ancestor we're checking against
  30  *
  31  * Return:
  32  *\li   boolean - is a at or below b?
  33  *
  34  * Notes:
  35  *\li   Trailing dots are first removed from name and domain.
  36  *      Always compare complete subdomains, not only whether the
  37  *      domain name is the trailing string of the given name.
  38  *
  39  *\li   "host.foobar.top" lies in "foobar.top" and in "top" and in ""
  40  *      but NOT in "bar.top"
  41  */
  42
  43 int
  44 ns_samedomain(const char *a, const char *b) {
  45         size_t la, lb;
  46         int diff, i, escaped;
  47         const char *cp;
  48
  49         la = strlen(a);
  50         lb = strlen(b);
  51
  52         /* Ignore a trailing label separator (i.e. an unescaped dot) in 'a'. */
  53         if (la != 0U && a[la - 1] == '.') {
  54                 escaped = 0;
  55                 /* Note this loop doesn't get executed if la==1. */
  56                 for (i = la - 2; i >= 0; i--)
  57                         if (a[i] == '\\') {
  58                                 if (escaped)
  59                                         escaped = 0;
  60                                 else
  61                                         escaped = 1;
  62                         } else
  63                                 break;
  64                 if (!escaped)
  65                         la--;
  66         }
  67
  68         /* Ignore a trailing label separator (i.e. an unescaped dot) in 'b'. */
  69         if (lb != 0U && b[lb - 1] == '.') {
  70                 escaped = 0;
  71                 /* note this loop doesn't get executed if lb==1 */
  72                 for (i = lb - 2; i >= 0; i--)
  73                         if (b[i] == '\\') {
  74                                 if (escaped)
  75                                         escaped = 0;
  76                                 else
  77                                         escaped = 1;
  78                         } else
  79                                 break;
  80                 if (!escaped)
  81                         lb--;
  82         }
  83
  84         /* lb == 0 means 'b' is the root domain, so 'a' must be in 'b'. */
  85         if (lb == 0U)
  86                 return (1);
  87
  88         /* 'b' longer than 'a' means 'a' can't be in 'b'. */
  89         if (lb > la)
  90                 return (0);
  91
  92         /* 'a' and 'b' being equal at this point indicates sameness. */
  93         if (lb == la)
  94                 return (strncasecmp(a, b, lb) == 0);
  95
  96         /* Ok, we know la > lb. */
  97
  98         diff = la - lb;
  99
 100         /*
 101          * If 'a' is only 1 character longer than 'b', then it can't be
 102          * a subdomain of 'b' (because of the need for the '.' label
 103          * separator).
 104          */
 105         if (diff < 2)
 106                 return (0);
 107
 108         /*
 109          * If the character before the last 'lb' characters of 'b'
 110          * isn't '.', then it can't be a match (this lets us avoid
 111          * having "foobar.com" match "bar.com").
 112          */
 113         if (a[diff - 1] != '.')
 114                 return (0);
 115
 116         /*
 117          * We're not sure about that '.', however.  It could be escaped
 118          * and thus not a really a label separator.
 119          */
 120         escaped = 0;
 121         for (i = diff - 2; i >= 0; i--)
 122                 if (a[i] == '\\') {
 123                         if (escaped)
 124                                 escaped = 0;
 125                         else
 126                                 escaped = 1;
 127                 } else
 128                         break;
 129         if (escaped)
 130                 return (0);
 131
 132         /* Now compare aligned trailing substring. */
 133         cp = a + diff;
 134         return (strncasecmp(cp, b, lb) == 0);
 135 }
 136 libresolv_hidden_def (ns_samedomain)
 137
 138 /*%
 139  *      is "a" a subdomain of "b"?
 140  */
 141 int
 142 ns_subdomain (const char *a, const char *b)
 143 {
 144   return __libc_ns_samename (a, b) != 1 && ns_samedomain (a, b);
 145 }
 146
 147 /*! \file */