"Fossies" - the Fresh Open Source Software Archive 
Member "udns-0.4/udns_parse.c" (5 Jul 2011, 5481 Bytes) of package /linux/misc/dns/udns-0.4.tar.gz:
As a special service "Fossies" has tried to format the requested source page into HTML format using (guessed) C and C++ source code syntax highlighting (style:
standard) with prefixed line numbers and
code folding option.
Alternatively you can here
view or
download the uninterpreted source code file.
For more information about "udns_parse.c" see the
Fossies "Dox" file reference documentation.
1 /* udns_parse.c
2 raw DNS packet parsing routines
3
4 Copyright (C) 2005 Michael Tokarev <mjt@corpit.ru>
5 This file is part of UDNS library, an async DNS stub resolver.
6
7 This library is free software; you can redistribute it and/or
8 modify it under the terms of the GNU Lesser General Public
9 License as published by the Free Software Foundation; either
10 version 2.1 of the License, or (at your option) any later version.
11
12 This library is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 Lesser General Public License for more details.
16
17 You should have received a copy of the GNU Lesser General Public
18 License along with this library, in file named COPYING.LGPL; if not,
19 write to the Free Software Foundation, Inc., 59 Temple Place,
20 Suite 330, Boston, MA 02111-1307 USA
21
22 */
23
24 #include <string.h>
25 #include <assert.h>
26 #include "udns.h"
27
28 dnscc_t *dns_skipdn(dnscc_t *cur, dnscc_t *end) {
29 unsigned c;
30 for(;;) {
31 if (cur >= end)
32 return NULL;
33 c = *cur++;
34 if (!c)
35 return cur;
36 if (c & 192) /* jump */
37 return cur + 1 >= end ? NULL : cur + 1;
38 cur += c;
39 }
40 }
41
42 int
43 dns_getdn(dnscc_t *pkt, dnscc_t **cur, dnscc_t *end,
44 register dnsc_t *dn, unsigned dnsiz) {
45 unsigned c;
46 dnscc_t *pp = *cur; /* current packet pointer */
47 dnsc_t *dp = dn; /* current dn pointer */
48 dnsc_t *const de /* end of the DN dest */
49 = dn + (dnsiz < DNS_MAXDN ? dnsiz : DNS_MAXDN);
50 dnscc_t *jump = NULL; /* ptr after first jump if any */
51 unsigned loop = 100; /* jump loop counter */
52
53 for(;;) { /* loop by labels */
54 if (pp >= end) /* reached end of packet? */
55 return -1;
56 c = *pp++; /* length of the label */
57 if (!c) { /* empty label: terminate */
58 if (dn >= de) /* can't fit terminator */
59 goto noroom;
60 *dp++ = 0;
61 /* return next pos: either after the first jump or current */
62 *cur = jump ? jump : pp;
63 return dp - dn;
64 }
65 if (c & 192) { /* jump */
66 if (pp >= end) /* eop instead of jump pos */
67 return -1;
68 if (!jump) jump = pp + 1; /* remember first jump */
69 else if (!--loop) return -1; /* too many jumps */
70 c = ((c & ~192) << 8) | *pp; /* new pos */
71 if (c < DNS_HSIZE) /* don't allow jump into the header */
72 return -1;
73 pp = pkt + c;
74 continue;
75 }
76 if (c > DNS_MAXLABEL) /* too long label? */
77 return -1;
78 if (pp + c > end) /* label does not fit in packet? */
79 return -1;
80 if (dp + c + 1 > de) /* if enouth room for the label */
81 goto noroom;
82 *dp++ = c; /* label length */
83 memcpy(dp, pp, c); /* and the label itself */
84 dp += c;
85 pp += c; /* advance to the next label */
86 }
87 noroom:
88 return dnsiz < DNS_MAXDN ? 0 : -1;
89 }
90
91 void dns_rewind(struct dns_parse *p, dnscc_t *qdn) {
92 p->dnsp_qdn = qdn;
93 p->dnsp_cur = p->dnsp_ans;
94 p->dnsp_rrl = dns_numan(p->dnsp_pkt);
95 p->dnsp_ttl = 0xffffffffu;
96 p->dnsp_nrr = 0;
97 }
98
99 void
100 dns_initparse(struct dns_parse *p, dnscc_t *qdn,
101 dnscc_t *pkt, dnscc_t *cur, dnscc_t *end) {
102 p->dnsp_pkt = pkt;
103 p->dnsp_end = end;
104 p->dnsp_rrl = dns_numan(pkt);
105 p->dnsp_qdn = qdn;
106 assert(cur + 4 <= end);
107 if ((p->dnsp_qtyp = dns_get16(cur+0)) == DNS_T_ANY) p->dnsp_qtyp = 0;
108 if ((p->dnsp_qcls = dns_get16(cur+2)) == DNS_C_ANY) p->dnsp_qcls = 0;
109 p->dnsp_cur = p->dnsp_ans = cur + 4;
110 p->dnsp_ttl = 0xffffffffu;
111 p->dnsp_nrr = 0;
112 }
113
114 int dns_nextrr(struct dns_parse *p, struct dns_rr *rr) {
115 dnscc_t *cur = p->dnsp_cur;
116 while(p->dnsp_rrl > 0) {
117 --p->dnsp_rrl;
118 if (dns_getdn(p->dnsp_pkt, &cur, p->dnsp_end,
119 rr->dnsrr_dn, sizeof(rr->dnsrr_dn)) <= 0)
120 return -1;
121 if (cur + 10 > p->dnsp_end)
122 return -1;
123 rr->dnsrr_typ = dns_get16(cur);
124 rr->dnsrr_cls = dns_get16(cur+2);
125 rr->dnsrr_ttl = dns_get32(cur+4);
126 rr->dnsrr_dsz = dns_get16(cur+8);
127 rr->dnsrr_dptr = cur = cur + 10;
128 rr->dnsrr_dend = cur = cur + rr->dnsrr_dsz;
129 if (cur > p->dnsp_end)
130 return -1;
131 if (p->dnsp_qdn && !dns_dnequal(p->dnsp_qdn, rr->dnsrr_dn))
132 continue;
133 if ((!p->dnsp_qcls || p->dnsp_qcls == rr->dnsrr_cls) &&
134 (!p->dnsp_qtyp || p->dnsp_qtyp == rr->dnsrr_typ)) {
135 p->dnsp_cur = cur;
136 ++p->dnsp_nrr;
137 if (p->dnsp_ttl > rr->dnsrr_ttl) p->dnsp_ttl = rr->dnsrr_ttl;
138 return 1;
139 }
140 if (p->dnsp_qdn && rr->dnsrr_typ == DNS_T_CNAME && !p->dnsp_nrr) {
141 if (dns_getdn(p->dnsp_pkt, &rr->dnsrr_dptr, p->dnsp_end,
142 p->dnsp_dnbuf, sizeof(p->dnsp_dnbuf)) <= 0 ||
143 rr->dnsrr_dptr != rr->dnsrr_dend)
144 return -1;
145 p->dnsp_qdn = p->dnsp_dnbuf;
146 if (p->dnsp_ttl > rr->dnsrr_ttl) p->dnsp_ttl = rr->dnsrr_ttl;
147 }
148 }
149 p->dnsp_cur = cur;
150 return 0;
151 }
152
153 int dns_stdrr_size(const struct dns_parse *p) {
154 return
155 dns_dntop_size(p->dnsp_qdn) +
156 (p->dnsp_qdn == dns_payload(p->dnsp_pkt) ? 0 :
157 dns_dntop_size(dns_payload(p->dnsp_pkt)));
158 }
159
160 void *dns_stdrr_finish(struct dns_rr_null *ret, char *cp,
161 const struct dns_parse *p) {
162 cp += dns_dntop(p->dnsp_qdn, (ret->dnsn_cname = cp), DNS_MAXNAME);
163 if (p->dnsp_qdn == dns_payload(p->dnsp_pkt))
164 ret->dnsn_qname = ret->dnsn_cname;
165 else
166 dns_dntop(dns_payload(p->dnsp_pkt), (ret->dnsn_qname = cp), DNS_MAXNAME);
167 ret->dnsn_ttl = p->dnsp_ttl;
168 return ret;
169 }