ares_expand_name.c
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/* 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
#include "ares_nameser.h"
#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, int is_hostname);
/* Reserved characters for names that need to be escaped */
static int is_reservedch(int ch)
{
switch (ch) {
case '"':
case '.':
case ';':
case '\\':
case '(':
case ')':
case '@':
case '$':
return 1;
default:
break;
}
return 0;
}
static int ares__isprint(int ch)
{
if (ch >= 0x20 && ch <= 0x7E)
return 1;
return 0;
}
/* Character set allowed by hostnames. This is to include the normal
* domain name character set plus:
* - underscores which are used in SRV records.
* - Forward slashes such as are used for classless in-addr.arpa
* delegation (CNAMEs)
* While RFC 2181 section 11 does state not to do validation,
* that applies to servers, not clients. Vulnerabilities have been
* reported when this validation is not performed. Security is more
* important than edge-case compatibility (which is probably invalid
* anyhow). */
static int is_hostnamech(int ch)
{
/* [A-Za-z0-9-._/]
* Don't use isalnum() as it is locale-specific
*/
if (ch >= 'A' && ch <= 'Z')
return 1;
if (ch >= 'a' && ch <= 'z')
return 1;
if (ch >= '0' && ch <= '9')
return 1;
if (ch == '-' || ch == '.' || ch == '_' || ch == '/')
return 1;
return 0;
}
/* 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.
*
* If the result is expected to be a hostname, then no escaped data is allowed
* and will return error.
*/
int ares__expand_name_validated(const unsigned char *encoded,
const unsigned char *abuf,
int alen, char **s, long *enclen,
int is_hostname)
{
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, is_hostname);
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
{
int name_len = *p;
len = name_len;
p++;
while (len--)
{
/* Output as \DDD for consistency with RFC1035 5.1, except
* for the special case of a root name response */
if (!ares__isprint(*p) && !(name_len == 1 && *p == 0))
{
*q++ = '\\';
*q++ = '0' + *p / 100;
*q++ = '0' + (*p % 100) / 10;
*q++ = '0' + (*p % 10);
}
else if (is_reservedch(*p))
{
*q++ = '\\';
*q++ = *p;
}
else
{
*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;
}
int ares_expand_name(const unsigned char *encoded, const unsigned char *abuf,
int alen, char **s, long *enclen)
{
return ares__expand_name_validated(encoded, abuf, alen, s, enclen, 0);
}
/* 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 is_hostname)
{
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)
{
int name_len = *encoded;
offset = name_len;
if (encoded + offset + 1 >= abuf + alen)
return -1;
encoded++;
while (offset--)
{
if (!ares__isprint(*encoded) && !(name_len == 1 && *encoded == 0))
{
if (is_hostname)
return -1;
n += 4;
}
else if (is_reservedch(*encoded))
{
if (is_hostname)
return -1;
n += 2;
}
else
{
if (is_hostname && !is_hostnamech(*encoded))
return -1;
n += 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_validated 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 is_hostname)
{
int status = ares__expand_name_validated(encoded, abuf, alen, s, enclen,
is_hostname);
if (status == ARES_EBADNAME)
status = ARES_EBADRESP;
return status;
}