2 /* Copyright 1998, 2011 by the Massachusetts Institute of Technology.
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.
17 #include "ares_setup.h"
19 #ifdef HAVE_SYS_SOCKET_H
20 # include <sys/socket.h>
22 #ifdef HAVE_NETINET_IN_H
23 # include <netinet/in.h>
25 #ifdef HAVE_ARPA_NAMESER_H
26 # include <arpa/nameser.h>
30 #ifdef HAVE_ARPA_NAMESER_COMPAT_H
31 # include <arpa/nameser_compat.h>
36 #include "ares_nowarn.h"
37 #include "ares_private.h" /* for the memdebug */
39 static int name_length(const unsigned char *encoded, const unsigned char *abuf,
42 /* Expand an RFC1035-encoded domain name given by encoded. The
43 * containing message is given by abuf and alen. The result given by
44 * *s, which is set to a NUL-terminated allocated buffer. *enclen is
45 * set to the length of the encoded name (not the length of the
46 * expanded name; the goal is to tell the caller how many bytes to
47 * move forward to get past the encoded name).
49 * In the simple case, an encoded name is a series of labels, each
50 * composed of a one-byte length (limited to values between 0 and 63
51 * inclusive) followed by the label contents. The name is terminated
52 * by a zero-length label.
54 * In the more complicated case, a label may be terminated by an
55 * indirection pointer, specified by two bytes with the high bits of
56 * the first byte (corresponding to INDIR_MASK) set to 11. With the
57 * two high bits of the first byte stripped off, the indirection
58 * pointer gives an offset from the beginning of the containing
59 * message with more labels to decode. Indirection can happen an
60 * arbitrary number of times, so we have to detect loops.
62 * Since the expanded name uses '.' as a label separator, we use
63 * backslashes to escape periods or backslashes in the expanded name.
66 int ares_expand_name(const unsigned char *encoded, const unsigned char *abuf,
67 int alen, char **s, long *enclen)
71 const unsigned char *p;
77 nlen.sig = name_length(encoded, abuf, alen);
81 *s = malloc(nlen.uns + 1);
87 /* RFC2181 says this should be ".": the root of the DNS tree.
88 * Since this function strips trailing dots though, it becomes ""
92 /* indirect root label (like 0xc0 0x0c) is 2 bytes long (stupid, but
94 if ((*encoded & INDIR_MASK) == INDIR_MASK)
97 *enclen = 1L; /* the caller should move one byte to get past this */
102 /* No error-checking necessary; it was all done by name_length(). */
106 if ((*p & INDIR_MASK) == INDIR_MASK)
110 *enclen = aresx_uztosl(p + 2U - encoded);
113 p = abuf + ((*p & ~INDIR_MASK) << 8 | *(p + 1));
121 if (*p == '.' || *p == '\\')
130 *enclen = aresx_uztosl(p + 1U - encoded);
132 /* Nuke the trailing period if we wrote one. */
136 *q = 0; /* zero terminate */
141 /* Return the length of the expansion of an encoded domain name, or
142 * -1 if the encoding is invalid.
144 static int name_length(const unsigned char *encoded, const unsigned char *abuf,
147 int n = 0, offset, indir = 0;
149 /* Allow the caller to pass us abuf + alen and have us check for it. */
150 if (encoded == abuf + alen)
155 if ((*encoded & INDIR_MASK) == INDIR_MASK)
157 /* Check the offset and go there. */
158 if (encoded + 1 >= abuf + alen)
160 offset = (*encoded & ~INDIR_MASK) << 8 | *(encoded + 1);
163 encoded = abuf + offset;
165 /* If we've seen more indirects than the message length,
166 * then there's a loop.
174 if (encoded + offset + 1 >= abuf + alen)
179 n += (*encoded == '.' || *encoded == '\\') ? 2 : 1;
186 /* If there were any labels at all, then the number of dots is one
187 * less than the number of labels, so subtract one.
189 return (n) ? n - 1 : n;
192 /* Like ares_expand_name but returns EBADRESP in case of invalid input. */
193 int ares__expand_name_for_response(const unsigned char *encoded,
194 const unsigned char *abuf, int alen,
195 char **s, long *enclen)
197 int status = ares_expand_name(encoded, abuf, alen, s, enclen);
198 if (status == ARES_EBADNAME)
199 status = ARES_EBADRESP;