[1765] | 1 | /* vi: set sw=4 ts=4: */
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| 2 |
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| 3 | /* RFC1035 domain compression routines (C) 2007 Gabriel Somlo <somlo at cmu.edu>
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| 4 | *
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| 5 | * Loosely based on the isc-dhcpd implementation by dhankins@isc.org
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| 6 | *
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[2725] | 7 | * Licensed under GPLv2 or later, see file LICENSE in this source tree.
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[1765] | 8 | */
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[2725] | 9 | #ifdef DNS_COMPR_TESTING
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[3621] | 10 | # define _GNU_SOURCE
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[2725] | 11 | # define FAST_FUNC /* nothing */
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| 12 | # define xmalloc malloc
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| 13 | # include <stdlib.h>
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| 14 | # include <stdint.h>
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| 15 | # include <string.h>
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| 16 | # include <stdio.h>
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| 17 | #else
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| 18 | # include "common.h"
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| 19 | #endif
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[1765] | 20 |
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| 21 | #define NS_MAXDNAME 1025 /* max domain name length */
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| 22 | #define NS_MAXCDNAME 255 /* max compressed domain name length */
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| 23 | #define NS_MAXLABEL 63 /* max label length */
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| 24 | #define NS_MAXDNSRCH 6 /* max domains in search path */
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| 25 | #define NS_CMPRSFLGS 0xc0 /* name compression pointer flag */
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| 26 |
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| 27 |
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[2725] | 28 | /* Expand a RFC1035-compressed list of domain names "cstr", of length "clen";
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[1765] | 29 | * returns a newly allocated string containing the space-separated domains,
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| 30 | * prefixed with the contents of string pre, or NULL if an error occurs.
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| 31 | */
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[2725] | 32 | char* FAST_FUNC dname_dec(const uint8_t *cstr, int clen, const char *pre)
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[1765] | 33 | {
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[2725] | 34 | char *ret = ret; /* for compiler */
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[1765] | 35 | char *dst = NULL;
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| 36 |
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| 37 | /* We make two passes over the cstr string. First, we compute
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| 38 | * how long the resulting string would be. Then we allocate a
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| 39 | * new buffer of the required length, and fill it in with the
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| 40 | * expanded content. The advantage of this approach is not
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| 41 | * having to deal with requiring callers to supply their own
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| 42 | * buffer, then having to check if it's sufficiently large, etc.
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| 43 | */
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[2725] | 44 | while (1) {
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| 45 | /* note: "return NULL" below are leak-safe since
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[3621] | 46 | * dst isn't allocated yet */
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[2725] | 47 | const uint8_t *c;
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| 48 | unsigned crtpos, retpos, depth, len;
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[1765] | 49 |
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| 50 | crtpos = retpos = depth = len = 0;
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| 51 | while (crtpos < clen) {
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| 52 | c = cstr + crtpos;
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| 53 |
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[2725] | 54 | if ((*c & NS_CMPRSFLGS) == NS_CMPRSFLGS) {
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| 55 | /* pointer */
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| 56 | if (crtpos + 2 > clen) /* no offset to jump to? abort */
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[1765] | 57 | return NULL;
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[2725] | 58 | if (retpos == 0) /* toplevel? save return spot */
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[1765] | 59 | retpos = crtpos + 2;
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| 60 | depth++;
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[2725] | 61 | crtpos = ((c[0] & 0x3f) << 8) | c[1]; /* jump */
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| 62 | } else if (*c) {
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| 63 | /* label */
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| 64 | if (crtpos + *c + 1 > clen) /* label too long? abort */
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[1765] | 65 | return NULL;
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| 66 | if (dst)
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[3621] | 67 | /* \3com ---> "com." */
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| 68 | ((char*)mempcpy(dst + len, c + 1, *c))[0] = '.';
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[1765] | 69 | len += *c + 1;
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| 70 | crtpos += *c + 1;
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[2725] | 71 | } else {
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| 72 | /* NUL: end of current domain name */
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| 73 | if (retpos == 0) {
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| 74 | /* toplevel? keep going */
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[1765] | 75 | crtpos++;
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[2725] | 76 | } else {
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| 77 | /* return to toplevel saved spot */
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[1765] | 78 | crtpos = retpos;
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| 79 | retpos = depth = 0;
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| 80 | }
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[3621] | 81 | if (dst && len != 0)
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| 82 | /* \4host\3com\0\4host and we are at \0:
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| 83 | * \3com was converted to "com.", change dot to space.
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| 84 | */
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[2725] | 85 | dst[len - 1] = ' ';
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[1765] | 86 | }
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| 87 |
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[2725] | 88 | if (depth > NS_MAXDNSRCH /* too many jumps? abort, it's a loop */
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| 89 | || len > NS_MAXDNAME * NS_MAXDNSRCH /* result too long? abort */
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| 90 | ) {
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[1765] | 91 | return NULL;
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[2725] | 92 | }
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[1765] | 93 | }
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| 94 |
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[2725] | 95 | if (!len) /* expanded string has 0 length? abort */
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[1765] | 96 | return NULL;
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| 97 |
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[2725] | 98 | if (!dst) { /* first pass? */
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| 99 | /* allocate dst buffer and copy pre */
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| 100 | unsigned plen = strlen(pre);
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[3621] | 101 | ret = xmalloc(plen + len);
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| 102 | dst = stpcpy(ret, pre);
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[2725] | 103 | } else {
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| 104 | dst[len - 1] = '\0';
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| 105 | break;
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| 106 | }
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[1765] | 107 | }
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| 108 |
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[2725] | 109 | return ret;
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[1765] | 110 | }
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| 111 |
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| 112 | /* Convert a domain name (src) from human-readable "foo.blah.com" format into
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| 113 | * RFC1035 encoding "\003foo\004blah\003com\000". Return allocated string, or
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| 114 | * NULL if an error occurs.
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| 115 | */
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| 116 | static uint8_t *convert_dname(const char *src)
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| 117 | {
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[2725] | 118 | uint8_t c, *res, *lenptr, *dst;
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[1765] | 119 | int len;
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| 120 |
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| 121 | res = xmalloc(strlen(src) + 2);
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[2725] | 122 | dst = lenptr = res;
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| 123 | dst++;
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[1765] | 124 |
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| 125 | for (;;) {
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| 126 | c = (uint8_t)*src++;
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[2725] | 127 | if (c == '.' || c == '\0') { /* end of label */
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| 128 | len = dst - lenptr - 1;
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[1765] | 129 | /* label too long, too short, or two '.'s in a row? abort */
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| 130 | if (len > NS_MAXLABEL || len == 0 || (c == '.' && *src == '.')) {
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| 131 | free(res);
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| 132 | return NULL;
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| 133 | }
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[2725] | 134 | *lenptr = len;
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| 135 | if (c == '\0' || *src == '\0') /* "" or ".": end of src */
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[1765] | 136 | break;
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[2725] | 137 | lenptr = dst++;
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| 138 | continue;
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[1765] | 139 | }
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[2725] | 140 | if (c >= 'A' && c <= 'Z') /* uppercase? convert to lower */
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| 141 | c += ('a' - 'A');
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| 142 | *dst++ = c;
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[1765] | 143 | }
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| 144 |
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[2725] | 145 | if (dst - res >= NS_MAXCDNAME) { /* dname too long? abort */
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[1765] | 146 | free(res);
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| 147 | return NULL;
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| 148 | }
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[2725] | 149 |
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| 150 | *dst = 0;
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[1765] | 151 | return res;
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| 152 | }
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| 153 |
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[2725] | 154 | /* Returns the offset within cstr at which dname can be found, or -1 */
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[1765] | 155 | static int find_offset(const uint8_t *cstr, int clen, const uint8_t *dname)
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| 156 | {
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| 157 | const uint8_t *c, *d;
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[2725] | 158 | int off;
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[1765] | 159 |
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| 160 | /* find all labels in cstr */
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| 161 | off = 0;
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| 162 | while (off < clen) {
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| 163 | c = cstr + off;
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| 164 |
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[2725] | 165 | if ((*c & NS_CMPRSFLGS) == NS_CMPRSFLGS) { /* pointer, skip */
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[1765] | 166 | off += 2;
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[2725] | 167 | continue;
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| 168 | }
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| 169 | if (*c) { /* label, try matching dname */
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[1765] | 170 | d = dname;
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[2725] | 171 | while (1) {
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| 172 | unsigned len1 = *c + 1;
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| 173 | if (memcmp(c, d, len1) != 0)
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| 174 | break;
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| 175 | if (len1 == 1) /* at terminating NUL - match, return offset */
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[1765] | 176 | return off;
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[2725] | 177 | d += len1;
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| 178 | c += len1;
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| 179 | if ((*c & NS_CMPRSFLGS) == NS_CMPRSFLGS) /* pointer, jump */
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| 180 | c = cstr + (((c[0] & 0x3f) << 8) | c[1]);
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[1765] | 181 | }
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[2725] | 182 | off += cstr[off] + 1;
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| 183 | continue;
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[1765] | 184 | }
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[2725] | 185 | /* NUL, skip */
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| 186 | off++;
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[1765] | 187 | }
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| 188 |
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| 189 | return -1;
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| 190 | }
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| 191 |
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[2725] | 192 | /* Computes string to be appended to cstr so that src would be added to
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[1765] | 193 | * the compression (best case, it's a 2-byte pointer to some offset within
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[2725] | 194 | * cstr; worst case, it's all of src, converted to <4>host<3>com<0> format).
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[1765] | 195 | * The computed string is returned directly; its length is returned via retlen;
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| 196 | * NULL and 0, respectively, are returned if an error occurs.
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| 197 | */
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[2725] | 198 | uint8_t* FAST_FUNC dname_enc(const uint8_t *cstr, int clen, const char *src, int *retlen)
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[1765] | 199 | {
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| 200 | uint8_t *d, *dname;
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| 201 | int off;
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| 202 |
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| 203 | dname = convert_dname(src);
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| 204 | if (dname == NULL) {
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| 205 | *retlen = 0;
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| 206 | return NULL;
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| 207 | }
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| 208 |
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[2725] | 209 | d = dname;
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| 210 | while (*d) {
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| 211 | if (cstr) {
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| 212 | off = find_offset(cstr, clen, d);
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| 213 | if (off >= 0) { /* found a match, add pointer and return */
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| 214 | *d++ = NS_CMPRSFLGS | (off >> 8);
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| 215 | *d = off;
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| 216 | break;
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| 217 | }
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[1765] | 218 | }
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[2725] | 219 | d += *d + 1;
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[1765] | 220 | }
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| 221 |
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| 222 | *retlen = d - dname + 1;
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| 223 | return dname;
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| 224 | }
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| 225 |
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[2725] | 226 | #ifdef DNS_COMPR_TESTING
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| 227 | /* gcc -Wall -DDNS_COMPR_TESTING domain_codec.c -o domain_codec && ./domain_codec */
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| 228 | int main(int argc, char **argv)
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| 229 | {
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| 230 | int len;
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| 231 | uint8_t *encoded;
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| 232 |
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[3621] | 233 | uint8_t str[6] = { 0x00, 0x00, 0x02, 0x65, 0x65, 0x00 };
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| 234 | printf("NUL:'%s'\n", dname_dec(str, 6, ""));
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| 235 |
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[2725] | 236 | #define DNAME_DEC(encoded,pre) dname_dec((uint8_t*)(encoded), sizeof(encoded), (pre))
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| 237 | printf("'%s'\n", DNAME_DEC("\4host\3com\0", "test1:"));
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| 238 | printf("test2:'%s'\n", DNAME_DEC("\4host\3com\0\4host\3com\0", ""));
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| 239 | printf("test3:'%s'\n", DNAME_DEC("\4host\3com\0\xC0\0", ""));
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| 240 | printf("test4:'%s'\n", DNAME_DEC("\4host\3com\0\xC0\5", ""));
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| 241 | printf("test5:'%s'\n", DNAME_DEC("\4host\3com\0\xC0\5\1z\xC0\xA", ""));
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| 242 |
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| 243 | #define DNAME_ENC(cache,source,lenp) dname_enc((uint8_t*)(cache), sizeof(cache), (source), (lenp))
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| 244 | encoded = dname_enc(NULL, 0, "test.net", &len);
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| 245 | printf("test6:'%s' len:%d\n", dname_dec(encoded, len, ""), len);
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| 246 | encoded = DNAME_ENC("\3net\0", "test.net", &len);
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| 247 | printf("test7:'%s' len:%d\n", dname_dec(encoded, len, ""), len);
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| 248 | encoded = DNAME_ENC("\4test\3net\0", "test.net", &len);
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| 249 | printf("test8:'%s' len:%d\n", dname_dec(encoded, len, ""), len);
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| 250 | return 0;
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| 251 | }
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| 252 | #endif
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