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