--- /dev/null
+
+/* Copyright 1998, 2011 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_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 "ares.h"
+#include "ares_nowarn.h"
+#include "ares_private.h" /* for the memdebug */
+
+/* Maximum number of indirections allowed for a name */
+#define MAX_INDIRS 50
+
+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;
+ union {
+ ares_ssize_t sig;
+ size_t uns;
+ } nlen;
+
+ nlen.sig = name_length(encoded, abuf, alen);
+ if (nlen.sig < 0)
+ return ARES_EBADNAME;
+
+ *s = ares_malloc(nlen.uns + 1);
+ if (!*s)
+ return ARES_ENOMEM;
+ q = *s;
+
+ if (nlen.uns == 0) {
+ /* RFC2181 says this should be ".": the root of the DNS tree.
+ * Since this function strips trailing dots though, it becomes ""
+ */
+ q[0] = '\0';
+
+ /* indirect root label (like 0xc0 0x0c) is 2 bytes long (stupid, but
+ valid) */
+ if ((*encoded & INDIR_MASK) == INDIR_MASK)
+ *enclen = 2L;
+ else
+ *enclen = 1L; /* 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 = aresx_uztosl(p + 2U - 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 = aresx_uztosl(p + 1U - encoded);
+
+ /* Nuke the trailing period if we wrote one. */
+ if (q > *s)
+ *(q - 1) = 0;
+ else
+ *q = 0; /* zero terminate; LCOV_EXCL_LINE: empty names exit above */
+
+ 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, top;
+
+ /* Allow the caller to pass us abuf + alen and have us check for it. */
+ if (encoded >= abuf + alen)
+ return -1;
+
+ while (*encoded)
+ {
+ top = (*encoded & INDIR_MASK);
+ if (top == 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.
+ */
+ ++indir;
+ if (indir > alen || indir > MAX_INDIRS)
+ return -1;
+ }
+ else if (top == 0x00)
+ {
+ offset = *encoded;
+ if (encoded + offset + 1 >= abuf + alen)
+ return -1;
+ encoded++;
+ while (offset--)
+ {
+ n += (*encoded == '.' || *encoded == '\\') ? 2 : 1;
+ encoded++;
+ }
+ n++;
+ }
+ else
+ {
+ /* RFC 1035 4.1.4 says other options (01, 10) for top 2
+ * bits are reserved.
+ */
+ return -1;
+ }
+ }
+
+ /* 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;
+}
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