1
2/* Copyright 1998 by the Massachusetts Institute of Technology.
3 *
4 * Permission to use, copy, modify, and distribute this
5 * software and its documentation for any purpose and without
6 * fee is hereby granted, provided that the above copyright
7 * notice appear in all copies and that both that copyright
8 * notice and this permission notice appear in supporting
9 * documentation, and that the name of M.I.T. not be used in
10 * advertising or publicity pertaining to distribution of the
11 * software without specific, written prior permission.
12 * M.I.T. makes no representations about the suitability of
13 * this software for any purpose.  It is provided "as is"
14 * without express or implied warranty.
15 */
16
17#include "ares_setup.h"
18
19#ifdef HAVE_SYS_SOCKET_H
20#  include <sys/socket.h>
21#endif
22#ifdef HAVE_NETINET_IN_H
23#  include <netinet/in.h>
24#endif
25#ifdef HAVE_ARPA_NAMESER_H
26#  include <arpa/nameser.h>
27#else
28#  include "nameser.h"
29#endif
30#ifdef HAVE_ARPA_NAMESER_COMPAT_H
31#  include <arpa/nameser_compat.h>
32#endif
33
34#include <stdlib.h>
35#include "ares.h"
36#include "ares_private.h" /* for the memdebug */
37
38static int name_length(const unsigned char *encoded, const unsigned char *abuf,
39                       int alen);
40
41/* Expand an RFC1035-encoded domain name given by encoded.  The
42 * containing message is given by abuf and alen.  The result given by
43 * *s, which is set to a NUL-terminated allocated buffer.  *enclen is
44 * set to the length of the encoded name (not the length of the
45 * expanded name; the goal is to tell the caller how many bytes to
46 * move forward to get past the encoded name).
47 *
48 * In the simple case, an encoded name is a series of labels, each
49 * composed of a one-byte length (limited to values between 0 and 63
50 * inclusive) followed by the label contents.  The name is terminated
51 * by a zero-length label.
52 *
53 * In the more complicated case, a label may be terminated by an
54 * indirection pointer, specified by two bytes with the high bits of
55 * the first byte (corresponding to INDIR_MASK) set to 11.  With the
56 * two high bits of the first byte stripped off, the indirection
57 * pointer gives an offset from the beginning of the containing
58 * message with more labels to decode.  Indirection can happen an
59 * arbitrary number of times, so we have to detect loops.
60 *
61 * Since the expanded name uses '.' as a label separator, we use
62 * backslashes to escape periods or backslashes in the expanded name.
63 */
64
65int ares_expand_name(const unsigned char *encoded, const unsigned char *abuf,
66                     int alen, char **s, long *enclen)
67{
68  int len, indir = 0;
69  char *q;
70  const unsigned char *p;
71  union {
72    ssize_t sig;
73     size_t uns;
74  } nlen;
75
76  nlen.sig = name_length(encoded, abuf, alen);
77  if (nlen.sig < 0)
78    return ARES_EBADNAME;
79
80  *s = malloc(nlen.uns + 1);
81  if (!*s)
82    return ARES_ENOMEM;
83  q = *s;
84
85  if (nlen.uns == 0) {
86    /* RFC2181 says this should be ".": the root of the DNS tree.
87     * Since this function strips trailing dots though, it becomes ""
88     */
89    q[0] = '\0';
90
91    /* indirect root label (like 0xc0 0x0c) is 2 bytes long (stupid, but
92       valid) */
93    if ((*encoded & INDIR_MASK) == INDIR_MASK)
94      *enclen = 2;
95    else
96      *enclen = 1;  /* the caller should move one byte to get past this */
97
98    return ARES_SUCCESS;
99  }
100
101  /* No error-checking necessary; it was all done by name_length(). */
102  p = encoded;
103  while (*p)
104    {
105      if ((*p & INDIR_MASK) == INDIR_MASK)
106        {
107          if (!indir)
108            {
109              *enclen = p + 2 - encoded;
110              indir = 1;
111            }
112          p = abuf + ((*p & ~INDIR_MASK) << 8 | *(p + 1));
113        }
114      else
115        {
116          len = *p;
117          p++;
118          while (len--)
119            {
120              if (*p == '.' || *p == '\\')
121                *q++ = '\\';
122              *q++ = *p;
123              p++;
124            }
125          *q++ = '.';
126        }
127    }
128  if (!indir)
129    *enclen = p + 1 - encoded;
130
131  /* Nuke the trailing period if we wrote one. */
132  if (q > *s)
133    *(q - 1) = 0;
134  else
135    *q = 0; /* zero terminate */
136
137  return ARES_SUCCESS;
138}
139
140/* Return the length of the expansion of an encoded domain name, or
141 * -1 if the encoding is invalid.
142 */
143static int name_length(const unsigned char *encoded, const unsigned char *abuf,
144                       int alen)
145{
146  int n = 0, offset, indir = 0;
147
148  /* Allow the caller to pass us abuf + alen and have us check for it. */
149  if (encoded == abuf + alen)
150    return -1;
151
152  while (*encoded)
153    {
154      if ((*encoded & INDIR_MASK) == INDIR_MASK)
155        {
156          /* Check the offset and go there. */
157          if (encoded + 1 >= abuf + alen)
158            return -1;
159          offset = (*encoded & ~INDIR_MASK) << 8 | *(encoded + 1);
160          if (offset >= alen)
161            return -1;
162          encoded = abuf + offset;
163
164          /* If we've seen more indirects than the message length,
165           * then there's a loop.
166           */
167          if (++indir > alen)
168            return -1;
169        }
170      else
171        {
172          offset = *encoded;
173          if (encoded + offset + 1 >= abuf + alen)
174            return -1;
175          encoded++;
176          while (offset--)
177            {
178              n += (*encoded == '.' || *encoded == '\\') ? 2 : 1;
179              encoded++;
180            }
181          n++;
182        }
183    }
184
185  /* If there were any labels at all, then the number of dots is one
186   * less than the number of labels, so subtract one.
187   */
188  return (n) ? n - 1 : n;
189}
190
191/* Like ares_expand_name but returns EBADRESP in case of invalid input. */
192int ares__expand_name_for_response(const unsigned char *encoded,
193                                   const unsigned char *abuf, int alen,
194                                   char **s, long *enclen)
195{
196  int status = ares_expand_name(encoded, abuf, alen, s, enclen);
197  if (status == ARES_EBADNAME)
198    status = ARES_EBADRESP;
199  return status;
200}
201