[1765] | 1 | /* vi: set sw=4 ts=4: */
|
---|
| 2 |
|
---|
| 3 | /* RFC1035 domain compression routines (C) 2007 Gabriel Somlo <somlo at cmu.edu>
|
---|
| 4 | *
|
---|
| 5 | * Loosely based on the isc-dhcpd implementation by dhankins@isc.org
|
---|
| 6 | *
|
---|
| 7 | * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
|
---|
| 8 | */
|
---|
| 9 |
|
---|
| 10 | #if ENABLE_FEATURE_RFC3397
|
---|
| 11 |
|
---|
| 12 | #include "common.h"
|
---|
| 13 | #include "options.h"
|
---|
| 14 |
|
---|
| 15 | #define NS_MAXDNAME 1025 /* max domain name length */
|
---|
| 16 | #define NS_MAXCDNAME 255 /* max compressed domain name length */
|
---|
| 17 | #define NS_MAXLABEL 63 /* max label length */
|
---|
| 18 | #define NS_MAXDNSRCH 6 /* max domains in search path */
|
---|
| 19 | #define NS_CMPRSFLGS 0xc0 /* name compression pointer flag */
|
---|
| 20 |
|
---|
| 21 |
|
---|
| 22 | /* expand a RFC1035-compressed list of domain names "cstr", of length "clen";
|
---|
| 23 | * returns a newly allocated string containing the space-separated domains,
|
---|
| 24 | * prefixed with the contents of string pre, or NULL if an error occurs.
|
---|
| 25 | */
|
---|
| 26 | char *dname_dec(const uint8_t *cstr, int clen, const char *pre)
|
---|
| 27 | {
|
---|
| 28 | const uint8_t *c;
|
---|
| 29 | int crtpos, retpos, depth, plen = 0, len = 0;
|
---|
| 30 | char *dst = NULL;
|
---|
| 31 |
|
---|
| 32 | if (!cstr)
|
---|
| 33 | return NULL;
|
---|
| 34 |
|
---|
| 35 | if (pre)
|
---|
| 36 | plen = strlen(pre);
|
---|
| 37 |
|
---|
| 38 | /* We make two passes over the cstr string. First, we compute
|
---|
| 39 | * how long the resulting string would be. Then we allocate a
|
---|
| 40 | * new buffer of the required length, and fill it in with the
|
---|
| 41 | * expanded content. The advantage of this approach is not
|
---|
| 42 | * having to deal with requiring callers to supply their own
|
---|
| 43 | * buffer, then having to check if it's sufficiently large, etc.
|
---|
| 44 | */
|
---|
| 45 |
|
---|
| 46 | while (!dst) {
|
---|
| 47 |
|
---|
| 48 | if (len > 0) { /* second pass? allocate dst buffer and copy pre */
|
---|
| 49 | dst = xmalloc(len + plen);
|
---|
| 50 | memcpy(dst, pre, plen);
|
---|
| 51 | }
|
---|
| 52 |
|
---|
| 53 | crtpos = retpos = depth = len = 0;
|
---|
| 54 |
|
---|
| 55 | while (crtpos < clen) {
|
---|
| 56 | c = cstr + crtpos;
|
---|
| 57 |
|
---|
| 58 | if ((*c & NS_CMPRSFLGS) != 0) { /* pointer */
|
---|
| 59 | if (crtpos + 2 > clen) /* no offset to jump to? abort */
|
---|
| 60 | return NULL;
|
---|
| 61 | if (retpos == 0) /* toplevel? save return spot */
|
---|
| 62 | retpos = crtpos + 2;
|
---|
| 63 | depth++;
|
---|
| 64 | crtpos = ((*c & 0x3f) << 8) | (*(c + 1) & 0xff); /* jump */
|
---|
| 65 | } else if (*c) { /* label */
|
---|
| 66 | if (crtpos + *c + 1 > clen) /* label too long? abort */
|
---|
| 67 | return NULL;
|
---|
| 68 | if (dst)
|
---|
| 69 | memcpy(dst + plen + len, c + 1, *c);
|
---|
| 70 | len += *c + 1;
|
---|
| 71 | crtpos += *c + 1;
|
---|
| 72 | if (dst)
|
---|
| 73 | *(dst + plen + len - 1) = '.';
|
---|
| 74 | } else { /* null: end of current domain name */
|
---|
| 75 | if (retpos == 0) { /* toplevel? keep going */
|
---|
| 76 | crtpos++;
|
---|
| 77 | } else { /* return to toplevel saved spot */
|
---|
| 78 | crtpos = retpos;
|
---|
| 79 | retpos = depth = 0;
|
---|
| 80 | }
|
---|
| 81 | if (dst)
|
---|
| 82 | *(dst + plen + len - 1) = ' ';
|
---|
| 83 | }
|
---|
| 84 |
|
---|
| 85 | if (depth > NS_MAXDNSRCH || /* too many jumps? abort, it's a loop */
|
---|
| 86 | len > NS_MAXDNAME * NS_MAXDNSRCH) /* result too long? abort */
|
---|
| 87 | return NULL;
|
---|
| 88 | }
|
---|
| 89 |
|
---|
| 90 | if (!len) /* expanded string has 0 length? abort */
|
---|
| 91 | return NULL;
|
---|
| 92 |
|
---|
| 93 | if (dst)
|
---|
| 94 | *(dst + plen + len - 1) = '\0';
|
---|
| 95 | }
|
---|
| 96 |
|
---|
| 97 | return dst;
|
---|
| 98 | }
|
---|
| 99 |
|
---|
| 100 | /* Convert a domain name (src) from human-readable "foo.blah.com" format into
|
---|
| 101 | * RFC1035 encoding "\003foo\004blah\003com\000". Return allocated string, or
|
---|
| 102 | * NULL if an error occurs.
|
---|
| 103 | */
|
---|
| 104 | static uint8_t *convert_dname(const char *src)
|
---|
| 105 | {
|
---|
| 106 | uint8_t c, *res, *lp, *rp;
|
---|
| 107 | int len;
|
---|
| 108 |
|
---|
| 109 | res = xmalloc(strlen(src) + 2);
|
---|
| 110 | rp = lp = res;
|
---|
| 111 | rp++;
|
---|
| 112 |
|
---|
| 113 | for (;;) {
|
---|
| 114 | c = (uint8_t)*src++;
|
---|
| 115 | if (c == '.' || c == '\0') { /* end of label */
|
---|
| 116 | len = rp - lp - 1;
|
---|
| 117 | /* label too long, too short, or two '.'s in a row? abort */
|
---|
| 118 | if (len > NS_MAXLABEL || len == 0 || (c == '.' && *src == '.')) {
|
---|
| 119 | free(res);
|
---|
| 120 | return NULL;
|
---|
| 121 | }
|
---|
| 122 | *lp = len;
|
---|
| 123 | lp = rp++;
|
---|
| 124 | if (c == '\0' || *src == '\0') /* end of dname */
|
---|
| 125 | break;
|
---|
| 126 | } else {
|
---|
| 127 | if (c >= 0x41 && c <= 0x5A) /* uppercase? convert to lower */
|
---|
| 128 | c += 0x20;
|
---|
| 129 | *rp++ = c;
|
---|
| 130 | }
|
---|
| 131 | }
|
---|
| 132 |
|
---|
| 133 | *lp = 0;
|
---|
| 134 | if (rp - res > NS_MAXCDNAME) { /* dname too long? abort */
|
---|
| 135 | free(res);
|
---|
| 136 | return NULL;
|
---|
| 137 | }
|
---|
| 138 | return res;
|
---|
| 139 | }
|
---|
| 140 |
|
---|
| 141 | /* returns the offset within cstr at which dname can be found, or -1
|
---|
| 142 | */
|
---|
| 143 | static int find_offset(const uint8_t *cstr, int clen, const uint8_t *dname)
|
---|
| 144 | {
|
---|
| 145 | const uint8_t *c, *d;
|
---|
| 146 | int off, inc;
|
---|
| 147 |
|
---|
| 148 | /* find all labels in cstr */
|
---|
| 149 | off = 0;
|
---|
| 150 | while (off < clen) {
|
---|
| 151 | c = cstr + off;
|
---|
| 152 |
|
---|
| 153 | if ((*c & NS_CMPRSFLGS) != 0) { /* pointer, skip */
|
---|
| 154 | off += 2;
|
---|
| 155 | } else if (*c) { /* label, try matching dname */
|
---|
| 156 | inc = *c + 1;
|
---|
| 157 | d = dname;
|
---|
| 158 | while (*c == *d && memcmp(c + 1, d + 1, *c) == 0) {
|
---|
| 159 | if (*c == 0) /* match, return offset */
|
---|
| 160 | return off;
|
---|
| 161 | d += *c + 1;
|
---|
| 162 | c += *c + 1;
|
---|
| 163 | if ((*c & NS_CMPRSFLGS) != 0) /* pointer, jump */
|
---|
| 164 | c = cstr + (((*c & 0x3f) << 8) | (*(c + 1) & 0xff));
|
---|
| 165 | }
|
---|
| 166 | off += inc;
|
---|
| 167 | } else { /* null, skip */
|
---|
| 168 | off++;
|
---|
| 169 | }
|
---|
| 170 | }
|
---|
| 171 |
|
---|
| 172 | return -1;
|
---|
| 173 | }
|
---|
| 174 |
|
---|
| 175 | /* computes string to be appended to cstr so that src would be added to
|
---|
| 176 | * the compression (best case, it's a 2-byte pointer to some offset within
|
---|
| 177 | * cstr; worst case, it's all of src, converted to rfc3011 format).
|
---|
| 178 | * The computed string is returned directly; its length is returned via retlen;
|
---|
| 179 | * NULL and 0, respectively, are returned if an error occurs.
|
---|
| 180 | */
|
---|
| 181 | uint8_t *dname_enc(const uint8_t *cstr, int clen, const char *src, int *retlen)
|
---|
| 182 | {
|
---|
| 183 | uint8_t *d, *dname;
|
---|
| 184 | int off;
|
---|
| 185 |
|
---|
| 186 | dname = convert_dname(src);
|
---|
| 187 | if (dname == NULL) {
|
---|
| 188 | *retlen = 0;
|
---|
| 189 | return NULL;
|
---|
| 190 | }
|
---|
| 191 |
|
---|
| 192 | for (d = dname; *d != 0; d += *d + 1) {
|
---|
| 193 | off = find_offset(cstr, clen, d);
|
---|
| 194 | if (off >= 0) { /* found a match, add pointer and terminate string */
|
---|
| 195 | *d++ = NS_CMPRSFLGS;
|
---|
| 196 | *d = off;
|
---|
| 197 | break;
|
---|
| 198 | }
|
---|
| 199 | }
|
---|
| 200 |
|
---|
| 201 | *retlen = d - dname + 1;
|
---|
| 202 | return dname;
|
---|
| 203 | }
|
---|
| 204 |
|
---|
| 205 | #endif /* ENABLE_FEATURE_RFC3397 */
|
---|