/* $Id: ares_expand_name.c,v 1.20 2009-11-02 11:55:53 yangtse Exp $ */ /* Copyright 1998 by the Massachusetts Institute of Technology. * * Permission to use, copy, modify, and distribute this * software and its documentation for any purpose and without * fee is hereby granted, provided that the above copyright * notice appear in all copies and that both that copyright * notice and this permission notice appear in supporting * documentation, and that the name of M.I.T. not be used in * advertising or publicity pertaining to distribution of the * software without specific, written prior permission. * M.I.T. makes no representations about the suitability of * this software for any purpose. It is provided "as is" * without express or implied warranty. */ #include "ares_setup.h" #ifdef HAVE_SYS_SOCKET_H # include <sys/socket.h> #endif #ifdef HAVE_NETINET_IN_H # include <netinet/in.h> #endif #ifdef HAVE_ARPA_NAMESER_H # include <arpa/nameser.h> #else # include "nameser.h" #endif #ifdef HAVE_ARPA_NAMESER_COMPAT_H # include <arpa/nameser_compat.h> #endif #include <stdlib.h> #include "ares.h" #include "ares_private.h" /* for the memdebug */ static int name_length(const unsigned char *encoded, const unsigned char *abuf, int alen); /* Expand an RFC1035-encoded domain name given by encoded. The * containing message is given by abuf and alen. The result given by * *s, which is set to a NUL-terminated allocated buffer. *enclen is * set to the length of the encoded name (not the length of the * expanded name; the goal is to tell the caller how many bytes to * move forward to get past the encoded name). * * In the simple case, an encoded name is a series of labels, each * composed of a one-byte length (limited to values between 0 and 63 * inclusive) followed by the label contents. The name is terminated * by a zero-length label. * * In the more complicated case, a label may be terminated by an * indirection pointer, specified by two bytes with the high bits of * the first byte (corresponding to INDIR_MASK) set to 11. With the * two high bits of the first byte stripped off, the indirection * pointer gives an offset from the beginning of the containing * message with more labels to decode. Indirection can happen an * arbitrary number of times, so we have to detect loops. * * Since the expanded name uses '.' as a label separator, we use * backslashes to escape periods or backslashes in the expanded name. */ int ares_expand_name(const unsigned char *encoded, const unsigned char *abuf, int alen, char **s, long *enclen) { int len, indir = 0; char *q; const unsigned char *p; len = name_length(encoded, abuf, alen); if (len < 0) return ARES_EBADNAME; *s = malloc(((size_t)len) + 1); if (!*s) return ARES_ENOMEM; q = *s; if (len == 0) { /* RFC2181 says this should be ".": the root of the DNS tree. * Since this function strips trailing dots though, it becomes "" */ q[0] = '\0'; *enclen = 1; /* the caller should move one byte to get past this */ return ARES_SUCCESS; } /* No error-checking necessary; it was all done by name_length(). */ p = encoded; while (*p) { if ((*p & INDIR_MASK) == INDIR_MASK) { if (!indir) { *enclen = p + 2 - encoded; indir = 1; } p = abuf + ((*p & ~INDIR_MASK) << 8 | *(p + 1)); } else { len = *p; p++; while (len--) { if (*p == '.' || *p == '\\') *q++ = '\\'; *q++ = *p; p++; } *q++ = '.'; } } if (!indir) *enclen = p + 1 - encoded; /* Nuke the trailing period if we wrote one. */ if (q > *s) *(q - 1) = 0; else *q = 0; /* zero terminate */ return ARES_SUCCESS; } /* Return the length of the expansion of an encoded domain name, or * -1 if the encoding is invalid. */ static int name_length(const unsigned char *encoded, const unsigned char *abuf, int alen) { int n = 0, offset, indir = 0; /* Allow the caller to pass us abuf + alen and have us check for it. */ if (encoded == abuf + alen) return -1; while (*encoded) { if ((*encoded & INDIR_MASK) == INDIR_MASK) { /* Check the offset and go there. */ if (encoded + 1 >= abuf + alen) return -1; offset = (*encoded & ~INDIR_MASK) << 8 | *(encoded + 1); if (offset >= alen) return -1; encoded = abuf + offset; /* If we've seen more indirects than the message length, * then there's a loop. */ if (++indir > alen) return -1; } else { offset = *encoded; if (encoded + offset + 1 >= abuf + alen) return -1; encoded++; while (offset--) { n += (*encoded == '.' || *encoded == '\\') ? 2 : 1; encoded++; } n++; } } /* If there were any labels at all, then the number of dots is one * less than the number of labels, so subtract one. */ return (n) ? n - 1 : n; } /* Like ares_expand_name but returns EBADRESP in case of invalid input. */ int ares__expand_name_for_response(const unsigned char *encoded, const unsigned char *abuf, int alen, char **s, long *enclen) { int status = ares_expand_name(encoded, abuf, alen, s, enclen); if (status == ARES_EBADNAME) status = ARES_EBADRESP; return status; }