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 38 static 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 65 int 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 */ 143 static 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. */ 192 int 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
