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206 lines
5.2 KiB
C
206 lines
5.2 KiB
C
/* vi: set sw=4 ts=4: */
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/* RFC1035 domain compression routines (C) 2007 Gabriel Somlo <somlo at cmu.edu>
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*
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* Loosely based on the isc-dhcpd implementation by dhankins@isc.org
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*
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* Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
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*/
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#if ENABLE_FEATURE_RFC3397
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#include "common.h"
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#include "options.h"
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#define NS_MAXDNAME 1025 /* max domain name length */
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#define NS_MAXCDNAME 255 /* max compressed domain name length */
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#define NS_MAXLABEL 63 /* max label length */
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#define NS_MAXDNSRCH 6 /* max domains in search path */
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#define NS_CMPRSFLGS 0xc0 /* name compression pointer flag */
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/* expand a RFC1035-compressed list of domain names "cstr", of length "clen";
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* returns a newly allocated string containing the space-separated domains,
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* prefixed with the contents of string pre, or NULL if an error occurs.
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*/
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char *dname_dec(const uint8_t *cstr, int clen, const char *pre)
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{
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const uint8_t *c;
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int crtpos, retpos, depth, plen = 0, len = 0;
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char *dst = NULL;
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if (!cstr)
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return NULL;
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if (pre)
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plen = strlen(pre);
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/* We make two passes over the cstr string. First, we compute
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* how long the resulting string would be. Then we allocate a
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* new buffer of the required length, and fill it in with the
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* expanded content. The advantage of this approach is not
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* having to deal with requiring callers to supply their own
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* buffer, then having to check if it's sufficiently large, etc.
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*/
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while (!dst) {
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if (len > 0) { /* second pass? allocate dst buffer and copy pre */
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dst = xmalloc(len + plen);
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memcpy(dst, pre, plen);
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}
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crtpos = retpos = depth = len = 0;
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while (crtpos < clen) {
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c = cstr + crtpos;
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if ((*c & NS_CMPRSFLGS) != 0) { /* pointer */
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if (crtpos + 2 > clen) /* no offset to jump to? abort */
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return NULL;
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if (retpos == 0) /* toplevel? save return spot */
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retpos = crtpos + 2;
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depth++;
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crtpos = ((*c & 0x3f) << 8) | (*(c + 1) & 0xff); /* jump */
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} else if (*c) { /* label */
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if (crtpos + *c + 1 > clen) /* label too long? abort */
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return NULL;
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if (dst)
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memcpy(dst + plen + len, c + 1, *c);
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len += *c + 1;
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crtpos += *c + 1;
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if (dst)
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*(dst + plen + len - 1) = '.';
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} else { /* null: end of current domain name */
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if (retpos == 0) { /* toplevel? keep going */
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crtpos++;
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} else { /* return to toplevel saved spot */
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crtpos = retpos;
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retpos = depth = 0;
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}
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if (dst)
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*(dst + plen + len - 1) = ' ';
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}
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if (depth > NS_MAXDNSRCH || /* too many jumps? abort, it's a loop */
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len > NS_MAXDNAME * NS_MAXDNSRCH) /* result too long? abort */
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return NULL;
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}
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if (!len) /* expanded string has 0 length? abort */
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return NULL;
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if (dst)
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*(dst + plen + len - 1) = '\0';
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}
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return dst;
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}
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/* Convert a domain name (src) from human-readable "foo.blah.com" format into
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* RFC1035 encoding "\003foo\004blah\003com\000". Return allocated string, or
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* NULL if an error occurs.
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*/
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static uint8_t *convert_dname(const char *src)
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{
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uint8_t c, *res, *lp, *rp;
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int len;
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res = xmalloc(strlen(src) + 2);
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rp = lp = res;
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rp++;
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for (;;) {
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c = (uint8_t)*src++;
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if (c == '.' || c == '\0') { /* end of label */
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len = rp - lp - 1;
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/* label too long, too short, or two '.'s in a row? abort */
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if (len > NS_MAXLABEL || len == 0 || (c == '.' && *src == '.')) {
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free(res);
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return NULL;
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}
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*lp = len;
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lp = rp++;
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if (c == '\0' || *src == '\0') /* end of dname */
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break;
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} else {
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if (c >= 0x41 && c <= 0x5A) /* uppercase? convert to lower */
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c += 0x20;
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*rp++ = c;
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}
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}
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*lp = 0;
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if (rp - res > NS_MAXCDNAME) { /* dname too long? abort */
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free(res);
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return NULL;
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}
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return res;
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}
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/* returns the offset within cstr at which dname can be found, or -1
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*/
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static int find_offset(const uint8_t *cstr, int clen, const uint8_t *dname)
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{
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const uint8_t *c, *d;
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int off, inc;
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/* find all labels in cstr */
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off = 0;
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while (off < clen) {
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c = cstr + off;
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if ((*c & NS_CMPRSFLGS) != 0) { /* pointer, skip */
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off += 2;
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} else if (*c) { /* label, try matching dname */
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inc = *c + 1;
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d = dname;
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while (*c == *d && memcmp(c + 1, d + 1, *c) == 0) {
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if (*c == 0) /* match, return offset */
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return off;
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d += *c + 1;
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c += *c + 1;
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if ((*c & NS_CMPRSFLGS) != 0) /* pointer, jump */
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c = cstr + (((*c & 0x3f) << 8) | (*(c + 1) & 0xff));
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}
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off += inc;
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} else { /* null, skip */
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off++;
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}
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}
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return -1;
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}
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/* computes string to be appended to cstr so that src would be added to
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* the compression (best case, it's a 2-byte pointer to some offset within
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* cstr; worst case, it's all of src, converted to rfc3011 format).
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* The computed string is returned directly; its length is returned via retlen;
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* NULL and 0, respectively, are returned if an error occurs.
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*/
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uint8_t *dname_enc(const uint8_t *cstr, int clen, const char *src, int *retlen)
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{
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uint8_t *d, *dname;
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int off;
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dname = convert_dname(src);
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if (dname == NULL) {
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*retlen = 0;
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return NULL;
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}
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for (d = dname; *d != 0; d += *d + 1) {
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off = find_offset(cstr, clen, d);
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if (off >= 0) { /* found a match, add pointer and terminate string */
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*d++ = NS_CMPRSFLGS;
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*d = off;
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break;
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}
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}
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*retlen = d - dname + 1;
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return dname;
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}
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#endif /* ENABLE_FEATURE_RFC3397 */
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