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Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-2.6.25
[deliverable/linux.git] / net / ipv4 / netfilter / nf_nat_snmp_basic.c
1 /*
2 * nf_nat_snmp_basic.c
3 *
4 * Basic SNMP Application Layer Gateway
5 *
6 * This IP NAT module is intended for use with SNMP network
7 * discovery and monitoring applications where target networks use
8 * conflicting private address realms.
9 *
10 * Static NAT is used to remap the networks from the view of the network
11 * management system at the IP layer, and this module remaps some application
12 * layer addresses to match.
13 *
14 * The simplest form of ALG is performed, where only tagged IP addresses
15 * are modified. The module does not need to be MIB aware and only scans
16 * messages at the ASN.1/BER level.
17 *
18 * Currently, only SNMPv1 and SNMPv2 are supported.
19 *
20 * More information on ALG and associated issues can be found in
21 * RFC 2962
22 *
23 * The ASB.1/BER parsing code is derived from the gxsnmp package by Gregory
24 * McLean & Jochen Friedrich, stripped down for use in the kernel.
25 *
26 * Copyright (c) 2000 RP Internet (www.rpi.net.au).
27 *
28 * This program is free software; you can redistribute it and/or modify
29 * it under the terms of the GNU General Public License as published by
30 * the Free Software Foundation; either version 2 of the License, or
31 * (at your option) any later version.
32 * This program is distributed in the hope that it will be useful,
33 * but WITHOUT ANY WARRANTY; without even the implied warranty of
34 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
35 * GNU General Public License for more details.
36 * You should have received a copy of the GNU General Public License
37 * along with this program; if not, write to the Free Software
38 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
39 *
40 * Author: James Morris <jmorris@intercode.com.au>
41 */
42 #include <linux/module.h>
43 #include <linux/moduleparam.h>
44 #include <linux/types.h>
45 #include <linux/kernel.h>
46 #include <linux/in.h>
47 #include <linux/ip.h>
48 #include <linux/udp.h>
49 #include <net/checksum.h>
50 #include <net/udp.h>
51
52 #include <net/netfilter/nf_nat.h>
53 #include <net/netfilter/nf_conntrack_helper.h>
54 #include <net/netfilter/nf_nat_helper.h>
55
56 MODULE_LICENSE("GPL");
57 MODULE_AUTHOR("James Morris <jmorris@intercode.com.au>");
58 MODULE_DESCRIPTION("Basic SNMP Application Layer Gateway");
59 MODULE_ALIAS("ip_nat_snmp_basic");
60
61 #define SNMP_PORT 161
62 #define SNMP_TRAP_PORT 162
63 #define NOCT1(n) (*(u8 *)(n))
64
65 static int debug;
66 static DEFINE_SPINLOCK(snmp_lock);
67
68 /*
69 * Application layer address mapping mimics the NAT mapping, but
70 * only for the first octet in this case (a more flexible system
71 * can be implemented if needed).
72 */
73 struct oct1_map
74 {
75 u_int8_t from;
76 u_int8_t to;
77 };
78
79
80 /*****************************************************************************
81 *
82 * Basic ASN.1 decoding routines (gxsnmp author Dirk Wisse)
83 *
84 *****************************************************************************/
85
86 /* Class */
87 #define ASN1_UNI 0 /* Universal */
88 #define ASN1_APL 1 /* Application */
89 #define ASN1_CTX 2 /* Context */
90 #define ASN1_PRV 3 /* Private */
91
92 /* Tag */
93 #define ASN1_EOC 0 /* End Of Contents */
94 #define ASN1_BOL 1 /* Boolean */
95 #define ASN1_INT 2 /* Integer */
96 #define ASN1_BTS 3 /* Bit String */
97 #define ASN1_OTS 4 /* Octet String */
98 #define ASN1_NUL 5 /* Null */
99 #define ASN1_OJI 6 /* Object Identifier */
100 #define ASN1_OJD 7 /* Object Description */
101 #define ASN1_EXT 8 /* External */
102 #define ASN1_SEQ 16 /* Sequence */
103 #define ASN1_SET 17 /* Set */
104 #define ASN1_NUMSTR 18 /* Numerical String */
105 #define ASN1_PRNSTR 19 /* Printable String */
106 #define ASN1_TEXSTR 20 /* Teletext String */
107 #define ASN1_VIDSTR 21 /* Video String */
108 #define ASN1_IA5STR 22 /* IA5 String */
109 #define ASN1_UNITIM 23 /* Universal Time */
110 #define ASN1_GENTIM 24 /* General Time */
111 #define ASN1_GRASTR 25 /* Graphical String */
112 #define ASN1_VISSTR 26 /* Visible String */
113 #define ASN1_GENSTR 27 /* General String */
114
115 /* Primitive / Constructed methods*/
116 #define ASN1_PRI 0 /* Primitive */
117 #define ASN1_CON 1 /* Constructed */
118
119 /*
120 * Error codes.
121 */
122 #define ASN1_ERR_NOERROR 0
123 #define ASN1_ERR_DEC_EMPTY 2
124 #define ASN1_ERR_DEC_EOC_MISMATCH 3
125 #define ASN1_ERR_DEC_LENGTH_MISMATCH 4
126 #define ASN1_ERR_DEC_BADVALUE 5
127
128 /*
129 * ASN.1 context.
130 */
131 struct asn1_ctx
132 {
133 int error; /* Error condition */
134 unsigned char *pointer; /* Octet just to be decoded */
135 unsigned char *begin; /* First octet */
136 unsigned char *end; /* Octet after last octet */
137 };
138
139 /*
140 * Octet string (not null terminated)
141 */
142 struct asn1_octstr
143 {
144 unsigned char *data;
145 unsigned int len;
146 };
147
148 static void asn1_open(struct asn1_ctx *ctx,
149 unsigned char *buf,
150 unsigned int len)
151 {
152 ctx->begin = buf;
153 ctx->end = buf + len;
154 ctx->pointer = buf;
155 ctx->error = ASN1_ERR_NOERROR;
156 }
157
158 static unsigned char asn1_octet_decode(struct asn1_ctx *ctx, unsigned char *ch)
159 {
160 if (ctx->pointer >= ctx->end) {
161 ctx->error = ASN1_ERR_DEC_EMPTY;
162 return 0;
163 }
164 *ch = *(ctx->pointer)++;
165 return 1;
166 }
167
168 static unsigned char asn1_tag_decode(struct asn1_ctx *ctx, unsigned int *tag)
169 {
170 unsigned char ch;
171
172 *tag = 0;
173
174 do
175 {
176 if (!asn1_octet_decode(ctx, &ch))
177 return 0;
178 *tag <<= 7;
179 *tag |= ch & 0x7F;
180 } while ((ch & 0x80) == 0x80);
181 return 1;
182 }
183
184 static unsigned char asn1_id_decode(struct asn1_ctx *ctx,
185 unsigned int *cls,
186 unsigned int *con,
187 unsigned int *tag)
188 {
189 unsigned char ch;
190
191 if (!asn1_octet_decode(ctx, &ch))
192 return 0;
193
194 *cls = (ch & 0xC0) >> 6;
195 *con = (ch & 0x20) >> 5;
196 *tag = (ch & 0x1F);
197
198 if (*tag == 0x1F) {
199 if (!asn1_tag_decode(ctx, tag))
200 return 0;
201 }
202 return 1;
203 }
204
205 static unsigned char asn1_length_decode(struct asn1_ctx *ctx,
206 unsigned int *def,
207 unsigned int *len)
208 {
209 unsigned char ch, cnt;
210
211 if (!asn1_octet_decode(ctx, &ch))
212 return 0;
213
214 if (ch == 0x80)
215 *def = 0;
216 else {
217 *def = 1;
218
219 if (ch < 0x80)
220 *len = ch;
221 else {
222 cnt = (unsigned char) (ch & 0x7F);
223 *len = 0;
224
225 while (cnt > 0) {
226 if (!asn1_octet_decode(ctx, &ch))
227 return 0;
228 *len <<= 8;
229 *len |= ch;
230 cnt--;
231 }
232 }
233 }
234 return 1;
235 }
236
237 static unsigned char asn1_header_decode(struct asn1_ctx *ctx,
238 unsigned char **eoc,
239 unsigned int *cls,
240 unsigned int *con,
241 unsigned int *tag)
242 {
243 unsigned int def, len;
244
245 if (!asn1_id_decode(ctx, cls, con, tag))
246 return 0;
247
248 def = len = 0;
249 if (!asn1_length_decode(ctx, &def, &len))
250 return 0;
251
252 if (def)
253 *eoc = ctx->pointer + len;
254 else
255 *eoc = NULL;
256 return 1;
257 }
258
259 static unsigned char asn1_eoc_decode(struct asn1_ctx *ctx, unsigned char *eoc)
260 {
261 unsigned char ch;
262
263 if (eoc == 0) {
264 if (!asn1_octet_decode(ctx, &ch))
265 return 0;
266
267 if (ch != 0x00) {
268 ctx->error = ASN1_ERR_DEC_EOC_MISMATCH;
269 return 0;
270 }
271
272 if (!asn1_octet_decode(ctx, &ch))
273 return 0;
274
275 if (ch != 0x00) {
276 ctx->error = ASN1_ERR_DEC_EOC_MISMATCH;
277 return 0;
278 }
279 return 1;
280 } else {
281 if (ctx->pointer != eoc) {
282 ctx->error = ASN1_ERR_DEC_LENGTH_MISMATCH;
283 return 0;
284 }
285 return 1;
286 }
287 }
288
289 static unsigned char asn1_null_decode(struct asn1_ctx *ctx, unsigned char *eoc)
290 {
291 ctx->pointer = eoc;
292 return 1;
293 }
294
295 static unsigned char asn1_long_decode(struct asn1_ctx *ctx,
296 unsigned char *eoc,
297 long *integer)
298 {
299 unsigned char ch;
300 unsigned int len;
301
302 if (!asn1_octet_decode(ctx, &ch))
303 return 0;
304
305 *integer = (signed char) ch;
306 len = 1;
307
308 while (ctx->pointer < eoc) {
309 if (++len > sizeof (long)) {
310 ctx->error = ASN1_ERR_DEC_BADVALUE;
311 return 0;
312 }
313
314 if (!asn1_octet_decode(ctx, &ch))
315 return 0;
316
317 *integer <<= 8;
318 *integer |= ch;
319 }
320 return 1;
321 }
322
323 static unsigned char asn1_uint_decode(struct asn1_ctx *ctx,
324 unsigned char *eoc,
325 unsigned int *integer)
326 {
327 unsigned char ch;
328 unsigned int len;
329
330 if (!asn1_octet_decode(ctx, &ch))
331 return 0;
332
333 *integer = ch;
334 if (ch == 0) len = 0;
335 else len = 1;
336
337 while (ctx->pointer < eoc) {
338 if (++len > sizeof (unsigned int)) {
339 ctx->error = ASN1_ERR_DEC_BADVALUE;
340 return 0;
341 }
342
343 if (!asn1_octet_decode(ctx, &ch))
344 return 0;
345
346 *integer <<= 8;
347 *integer |= ch;
348 }
349 return 1;
350 }
351
352 static unsigned char asn1_ulong_decode(struct asn1_ctx *ctx,
353 unsigned char *eoc,
354 unsigned long *integer)
355 {
356 unsigned char ch;
357 unsigned int len;
358
359 if (!asn1_octet_decode(ctx, &ch))
360 return 0;
361
362 *integer = ch;
363 if (ch == 0) len = 0;
364 else len = 1;
365
366 while (ctx->pointer < eoc) {
367 if (++len > sizeof (unsigned long)) {
368 ctx->error = ASN1_ERR_DEC_BADVALUE;
369 return 0;
370 }
371
372 if (!asn1_octet_decode(ctx, &ch))
373 return 0;
374
375 *integer <<= 8;
376 *integer |= ch;
377 }
378 return 1;
379 }
380
381 static unsigned char asn1_octets_decode(struct asn1_ctx *ctx,
382 unsigned char *eoc,
383 unsigned char **octets,
384 unsigned int *len)
385 {
386 unsigned char *ptr;
387
388 *len = 0;
389
390 *octets = kmalloc(eoc - ctx->pointer, GFP_ATOMIC);
391 if (*octets == NULL) {
392 if (net_ratelimit())
393 printk("OOM in bsalg (%d)\n", __LINE__);
394 return 0;
395 }
396
397 ptr = *octets;
398 while (ctx->pointer < eoc) {
399 if (!asn1_octet_decode(ctx, (unsigned char *)ptr++)) {
400 kfree(*octets);
401 *octets = NULL;
402 return 0;
403 }
404 (*len)++;
405 }
406 return 1;
407 }
408
409 static unsigned char asn1_subid_decode(struct asn1_ctx *ctx,
410 unsigned long *subid)
411 {
412 unsigned char ch;
413
414 *subid = 0;
415
416 do {
417 if (!asn1_octet_decode(ctx, &ch))
418 return 0;
419
420 *subid <<= 7;
421 *subid |= ch & 0x7F;
422 } while ((ch & 0x80) == 0x80);
423 return 1;
424 }
425
426 static unsigned char asn1_oid_decode(struct asn1_ctx *ctx,
427 unsigned char *eoc,
428 unsigned long **oid,
429 unsigned int *len)
430 {
431 unsigned long subid;
432 unsigned int size;
433 unsigned long *optr;
434
435 size = eoc - ctx->pointer + 1;
436 *oid = kmalloc(size * sizeof(unsigned long), GFP_ATOMIC);
437 if (*oid == NULL) {
438 if (net_ratelimit())
439 printk("OOM in bsalg (%d)\n", __LINE__);
440 return 0;
441 }
442
443 optr = *oid;
444
445 if (!asn1_subid_decode(ctx, &subid)) {
446 kfree(*oid);
447 *oid = NULL;
448 return 0;
449 }
450
451 if (subid < 40) {
452 optr [0] = 0;
453 optr [1] = subid;
454 } else if (subid < 80) {
455 optr [0] = 1;
456 optr [1] = subid - 40;
457 } else {
458 optr [0] = 2;
459 optr [1] = subid - 80;
460 }
461
462 *len = 2;
463 optr += 2;
464
465 while (ctx->pointer < eoc) {
466 if (++(*len) > size) {
467 ctx->error = ASN1_ERR_DEC_BADVALUE;
468 kfree(*oid);
469 *oid = NULL;
470 return 0;
471 }
472
473 if (!asn1_subid_decode(ctx, optr++)) {
474 kfree(*oid);
475 *oid = NULL;
476 return 0;
477 }
478 }
479 return 1;
480 }
481
482 /*****************************************************************************
483 *
484 * SNMP decoding routines (gxsnmp author Dirk Wisse)
485 *
486 *****************************************************************************/
487
488 /* SNMP Versions */
489 #define SNMP_V1 0
490 #define SNMP_V2C 1
491 #define SNMP_V2 2
492 #define SNMP_V3 3
493
494 /* Default Sizes */
495 #define SNMP_SIZE_COMM 256
496 #define SNMP_SIZE_OBJECTID 128
497 #define SNMP_SIZE_BUFCHR 256
498 #define SNMP_SIZE_BUFINT 128
499 #define SNMP_SIZE_SMALLOBJECTID 16
500
501 /* Requests */
502 #define SNMP_PDU_GET 0
503 #define SNMP_PDU_NEXT 1
504 #define SNMP_PDU_RESPONSE 2
505 #define SNMP_PDU_SET 3
506 #define SNMP_PDU_TRAP1 4
507 #define SNMP_PDU_BULK 5
508 #define SNMP_PDU_INFORM 6
509 #define SNMP_PDU_TRAP2 7
510
511 /* Errors */
512 #define SNMP_NOERROR 0
513 #define SNMP_TOOBIG 1
514 #define SNMP_NOSUCHNAME 2
515 #define SNMP_BADVALUE 3
516 #define SNMP_READONLY 4
517 #define SNMP_GENERROR 5
518 #define SNMP_NOACCESS 6
519 #define SNMP_WRONGTYPE 7
520 #define SNMP_WRONGLENGTH 8
521 #define SNMP_WRONGENCODING 9
522 #define SNMP_WRONGVALUE 10
523 #define SNMP_NOCREATION 11
524 #define SNMP_INCONSISTENTVALUE 12
525 #define SNMP_RESOURCEUNAVAILABLE 13
526 #define SNMP_COMMITFAILED 14
527 #define SNMP_UNDOFAILED 15
528 #define SNMP_AUTHORIZATIONERROR 16
529 #define SNMP_NOTWRITABLE 17
530 #define SNMP_INCONSISTENTNAME 18
531
532 /* General SNMP V1 Traps */
533 #define SNMP_TRAP_COLDSTART 0
534 #define SNMP_TRAP_WARMSTART 1
535 #define SNMP_TRAP_LINKDOWN 2
536 #define SNMP_TRAP_LINKUP 3
537 #define SNMP_TRAP_AUTFAILURE 4
538 #define SNMP_TRAP_EQPNEIGHBORLOSS 5
539 #define SNMP_TRAP_ENTSPECIFIC 6
540
541 /* SNMPv1 Types */
542 #define SNMP_NULL 0
543 #define SNMP_INTEGER 1 /* l */
544 #define SNMP_OCTETSTR 2 /* c */
545 #define SNMP_DISPLAYSTR 2 /* c */
546 #define SNMP_OBJECTID 3 /* ul */
547 #define SNMP_IPADDR 4 /* uc */
548 #define SNMP_COUNTER 5 /* ul */
549 #define SNMP_GAUGE 6 /* ul */
550 #define SNMP_TIMETICKS 7 /* ul */
551 #define SNMP_OPAQUE 8 /* c */
552
553 /* Additional SNMPv2 Types */
554 #define SNMP_UINTEGER 5 /* ul */
555 #define SNMP_BITSTR 9 /* uc */
556 #define SNMP_NSAP 10 /* uc */
557 #define SNMP_COUNTER64 11 /* ul */
558 #define SNMP_NOSUCHOBJECT 12
559 #define SNMP_NOSUCHINSTANCE 13
560 #define SNMP_ENDOFMIBVIEW 14
561
562 union snmp_syntax
563 {
564 unsigned char uc[0]; /* 8 bit unsigned */
565 char c[0]; /* 8 bit signed */
566 unsigned long ul[0]; /* 32 bit unsigned */
567 long l[0]; /* 32 bit signed */
568 };
569
570 struct snmp_object
571 {
572 unsigned long *id;
573 unsigned int id_len;
574 unsigned short type;
575 unsigned int syntax_len;
576 union snmp_syntax syntax;
577 };
578
579 struct snmp_request
580 {
581 unsigned long id;
582 unsigned int error_status;
583 unsigned int error_index;
584 };
585
586 struct snmp_v1_trap
587 {
588 unsigned long *id;
589 unsigned int id_len;
590 unsigned long ip_address; /* pointer */
591 unsigned int general;
592 unsigned int specific;
593 unsigned long time;
594 };
595
596 /* SNMP types */
597 #define SNMP_IPA 0
598 #define SNMP_CNT 1
599 #define SNMP_GGE 2
600 #define SNMP_TIT 3
601 #define SNMP_OPQ 4
602 #define SNMP_C64 6
603
604 /* SNMP errors */
605 #define SERR_NSO 0
606 #define SERR_NSI 1
607 #define SERR_EOM 2
608
609 static inline void mangle_address(unsigned char *begin,
610 unsigned char *addr,
611 const struct oct1_map *map,
612 __sum16 *check);
613 struct snmp_cnv
614 {
615 unsigned int class;
616 unsigned int tag;
617 int syntax;
618 };
619
620 static struct snmp_cnv snmp_conv [] =
621 {
622 {ASN1_UNI, ASN1_NUL, SNMP_NULL},
623 {ASN1_UNI, ASN1_INT, SNMP_INTEGER},
624 {ASN1_UNI, ASN1_OTS, SNMP_OCTETSTR},
625 {ASN1_UNI, ASN1_OTS, SNMP_DISPLAYSTR},
626 {ASN1_UNI, ASN1_OJI, SNMP_OBJECTID},
627 {ASN1_APL, SNMP_IPA, SNMP_IPADDR},
628 {ASN1_APL, SNMP_CNT, SNMP_COUNTER}, /* Counter32 */
629 {ASN1_APL, SNMP_GGE, SNMP_GAUGE}, /* Gauge32 == Unsigned32 */
630 {ASN1_APL, SNMP_TIT, SNMP_TIMETICKS},
631 {ASN1_APL, SNMP_OPQ, SNMP_OPAQUE},
632
633 /* SNMPv2 data types and errors */
634 {ASN1_UNI, ASN1_BTS, SNMP_BITSTR},
635 {ASN1_APL, SNMP_C64, SNMP_COUNTER64},
636 {ASN1_CTX, SERR_NSO, SNMP_NOSUCHOBJECT},
637 {ASN1_CTX, SERR_NSI, SNMP_NOSUCHINSTANCE},
638 {ASN1_CTX, SERR_EOM, SNMP_ENDOFMIBVIEW},
639 {0, 0, -1}
640 };
641
642 static unsigned char snmp_tag_cls2syntax(unsigned int tag,
643 unsigned int cls,
644 unsigned short *syntax)
645 {
646 struct snmp_cnv *cnv;
647
648 cnv = snmp_conv;
649
650 while (cnv->syntax != -1) {
651 if (cnv->tag == tag && cnv->class == cls) {
652 *syntax = cnv->syntax;
653 return 1;
654 }
655 cnv++;
656 }
657 return 0;
658 }
659
660 static unsigned char snmp_object_decode(struct asn1_ctx *ctx,
661 struct snmp_object **obj)
662 {
663 unsigned int cls, con, tag, len, idlen;
664 unsigned short type;
665 unsigned char *eoc, *end, *p;
666 unsigned long *lp, *id;
667 unsigned long ul;
668 long l;
669
670 *obj = NULL;
671 id = NULL;
672
673 if (!asn1_header_decode(ctx, &eoc, &cls, &con, &tag))
674 return 0;
675
676 if (cls != ASN1_UNI || con != ASN1_CON || tag != ASN1_SEQ)
677 return 0;
678
679 if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
680 return 0;
681
682 if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_OJI)
683 return 0;
684
685 if (!asn1_oid_decode(ctx, end, &id, &idlen))
686 return 0;
687
688 if (!asn1_header_decode(ctx, &end, &cls, &con, &tag)) {
689 kfree(id);
690 return 0;
691 }
692
693 if (con != ASN1_PRI) {
694 kfree(id);
695 return 0;
696 }
697
698 type = 0;
699 if (!snmp_tag_cls2syntax(tag, cls, &type)) {
700 kfree(id);
701 return 0;
702 }
703
704 l = 0;
705 switch (type) {
706 case SNMP_INTEGER:
707 len = sizeof(long);
708 if (!asn1_long_decode(ctx, end, &l)) {
709 kfree(id);
710 return 0;
711 }
712 *obj = kmalloc(sizeof(struct snmp_object) + len,
713 GFP_ATOMIC);
714 if (*obj == NULL) {
715 kfree(id);
716 if (net_ratelimit())
717 printk("OOM in bsalg (%d)\n", __LINE__);
718 return 0;
719 }
720 (*obj)->syntax.l[0] = l;
721 break;
722 case SNMP_OCTETSTR:
723 case SNMP_OPAQUE:
724 if (!asn1_octets_decode(ctx, end, &p, &len)) {
725 kfree(id);
726 return 0;
727 }
728 *obj = kmalloc(sizeof(struct snmp_object) + len,
729 GFP_ATOMIC);
730 if (*obj == NULL) {
731 kfree(id);
732 if (net_ratelimit())
733 printk("OOM in bsalg (%d)\n", __LINE__);
734 return 0;
735 }
736 memcpy((*obj)->syntax.c, p, len);
737 kfree(p);
738 break;
739 case SNMP_NULL:
740 case SNMP_NOSUCHOBJECT:
741 case SNMP_NOSUCHINSTANCE:
742 case SNMP_ENDOFMIBVIEW:
743 len = 0;
744 *obj = kmalloc(sizeof(struct snmp_object), GFP_ATOMIC);
745 if (*obj == NULL) {
746 kfree(id);
747 if (net_ratelimit())
748 printk("OOM in bsalg (%d)\n", __LINE__);
749 return 0;
750 }
751 if (!asn1_null_decode(ctx, end)) {
752 kfree(id);
753 kfree(*obj);
754 *obj = NULL;
755 return 0;
756 }
757 break;
758 case SNMP_OBJECTID:
759 if (!asn1_oid_decode(ctx, end, (unsigned long **)&lp, &len)) {
760 kfree(id);
761 return 0;
762 }
763 len *= sizeof(unsigned long);
764 *obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
765 if (*obj == NULL) {
766 kfree(lp);
767 kfree(id);
768 if (net_ratelimit())
769 printk("OOM in bsalg (%d)\n", __LINE__);
770 return 0;
771 }
772 memcpy((*obj)->syntax.ul, lp, len);
773 kfree(lp);
774 break;
775 case SNMP_IPADDR:
776 if (!asn1_octets_decode(ctx, end, &p, &len)) {
777 kfree(id);
778 return 0;
779 }
780 if (len != 4) {
781 kfree(p);
782 kfree(id);
783 return 0;
784 }
785 *obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
786 if (*obj == NULL) {
787 kfree(p);
788 kfree(id);
789 if (net_ratelimit())
790 printk("OOM in bsalg (%d)\n", __LINE__);
791 return 0;
792 }
793 memcpy((*obj)->syntax.uc, p, len);
794 kfree(p);
795 break;
796 case SNMP_COUNTER:
797 case SNMP_GAUGE:
798 case SNMP_TIMETICKS:
799 len = sizeof(unsigned long);
800 if (!asn1_ulong_decode(ctx, end, &ul)) {
801 kfree(id);
802 return 0;
803 }
804 *obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
805 if (*obj == NULL) {
806 kfree(id);
807 if (net_ratelimit())
808 printk("OOM in bsalg (%d)\n", __LINE__);
809 return 0;
810 }
811 (*obj)->syntax.ul[0] = ul;
812 break;
813 default:
814 kfree(id);
815 return 0;
816 }
817
818 (*obj)->syntax_len = len;
819 (*obj)->type = type;
820 (*obj)->id = id;
821 (*obj)->id_len = idlen;
822
823 if (!asn1_eoc_decode(ctx, eoc)) {
824 kfree(id);
825 kfree(*obj);
826 *obj = NULL;
827 return 0;
828 }
829 return 1;
830 }
831
832 static unsigned char snmp_request_decode(struct asn1_ctx *ctx,
833 struct snmp_request *request)
834 {
835 unsigned int cls, con, tag;
836 unsigned char *end;
837
838 if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
839 return 0;
840
841 if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
842 return 0;
843
844 if (!asn1_ulong_decode(ctx, end, &request->id))
845 return 0;
846
847 if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
848 return 0;
849
850 if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
851 return 0;
852
853 if (!asn1_uint_decode(ctx, end, &request->error_status))
854 return 0;
855
856 if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
857 return 0;
858
859 if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
860 return 0;
861
862 if (!asn1_uint_decode(ctx, end, &request->error_index))
863 return 0;
864
865 return 1;
866 }
867
868 /*
869 * Fast checksum update for possibly oddly-aligned UDP byte, from the
870 * code example in the draft.
871 */
872 static void fast_csum(__sum16 *csum,
873 const unsigned char *optr,
874 const unsigned char *nptr,
875 int offset)
876 {
877 unsigned char s[4];
878
879 if (offset & 1) {
880 s[0] = s[2] = 0;
881 s[1] = ~*optr;
882 s[3] = *nptr;
883 } else {
884 s[1] = s[3] = 0;
885 s[0] = ~*optr;
886 s[2] = *nptr;
887 }
888
889 *csum = csum_fold(csum_partial(s, 4, ~csum_unfold(*csum)));
890 }
891
892 /*
893 * Mangle IP address.
894 * - begin points to the start of the snmp messgae
895 * - addr points to the start of the address
896 */
897 static inline void mangle_address(unsigned char *begin,
898 unsigned char *addr,
899 const struct oct1_map *map,
900 __sum16 *check)
901 {
902 if (map->from == NOCT1(addr)) {
903 u_int32_t old;
904
905 if (debug)
906 memcpy(&old, (unsigned char *)addr, sizeof(old));
907
908 *addr = map->to;
909
910 /* Update UDP checksum if being used */
911 if (*check) {
912 fast_csum(check,
913 &map->from, &map->to, addr - begin);
914
915 }
916
917 if (debug)
918 printk(KERN_DEBUG "bsalg: mapped %u.%u.%u.%u to "
919 "%u.%u.%u.%u\n", NIPQUAD(old), NIPQUAD(*addr));
920 }
921 }
922
923 static unsigned char snmp_trap_decode(struct asn1_ctx *ctx,
924 struct snmp_v1_trap *trap,
925 const struct oct1_map *map,
926 __sum16 *check)
927 {
928 unsigned int cls, con, tag, len;
929 unsigned char *end;
930
931 if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
932 return 0;
933
934 if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_OJI)
935 return 0;
936
937 if (!asn1_oid_decode(ctx, end, &trap->id, &trap->id_len))
938 return 0;
939
940 if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
941 goto err_id_free;
942
943 if (!((cls == ASN1_APL && con == ASN1_PRI && tag == SNMP_IPA) ||
944 (cls == ASN1_UNI && con == ASN1_PRI && tag == ASN1_OTS)))
945 goto err_id_free;
946
947 if (!asn1_octets_decode(ctx, end, (unsigned char **)&trap->ip_address, &len))
948 goto err_id_free;
949
950 /* IPv4 only */
951 if (len != 4)
952 goto err_addr_free;
953
954 mangle_address(ctx->begin, ctx->pointer - 4, map, check);
955
956 if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
957 goto err_addr_free;
958
959 if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
960 goto err_addr_free;
961
962 if (!asn1_uint_decode(ctx, end, &trap->general))
963 goto err_addr_free;
964
965 if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
966 goto err_addr_free;
967
968 if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
969 goto err_addr_free;
970
971 if (!asn1_uint_decode(ctx, end, &trap->specific))
972 goto err_addr_free;
973
974 if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
975 goto err_addr_free;
976
977 if (!((cls == ASN1_APL && con == ASN1_PRI && tag == SNMP_TIT) ||
978 (cls == ASN1_UNI && con == ASN1_PRI && tag == ASN1_INT)))
979 goto err_addr_free;
980
981 if (!asn1_ulong_decode(ctx, end, &trap->time))
982 goto err_addr_free;
983
984 return 1;
985
986 err_addr_free:
987 kfree((unsigned long *)trap->ip_address);
988
989 err_id_free:
990 kfree(trap->id);
991
992 return 0;
993 }
994
995 /*****************************************************************************
996 *
997 * Misc. routines
998 *
999 *****************************************************************************/
1000
1001 static void hex_dump(unsigned char *buf, size_t len)
1002 {
1003 size_t i;
1004
1005 for (i = 0; i < len; i++) {
1006 if (i && !(i % 16))
1007 printk("\n");
1008 printk("%02x ", *(buf + i));
1009 }
1010 printk("\n");
1011 }
1012
1013 /*
1014 * Parse and mangle SNMP message according to mapping.
1015 * (And this is the fucking 'basic' method).
1016 */
1017 static int snmp_parse_mangle(unsigned char *msg,
1018 u_int16_t len,
1019 const struct oct1_map *map,
1020 __sum16 *check)
1021 {
1022 unsigned char *eoc, *end;
1023 unsigned int cls, con, tag, vers, pdutype;
1024 struct asn1_ctx ctx;
1025 struct asn1_octstr comm;
1026 struct snmp_object **obj;
1027
1028 if (debug > 1)
1029 hex_dump(msg, len);
1030
1031 asn1_open(&ctx, msg, len);
1032
1033 /*
1034 * Start of SNMP message.
1035 */
1036 if (!asn1_header_decode(&ctx, &eoc, &cls, &con, &tag))
1037 return 0;
1038 if (cls != ASN1_UNI || con != ASN1_CON || tag != ASN1_SEQ)
1039 return 0;
1040
1041 /*
1042 * Version 1 or 2 handled.
1043 */
1044 if (!asn1_header_decode(&ctx, &end, &cls, &con, &tag))
1045 return 0;
1046 if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
1047 return 0;
1048 if (!asn1_uint_decode (&ctx, end, &vers))
1049 return 0;
1050 if (debug > 1)
1051 printk(KERN_DEBUG "bsalg: snmp version: %u\n", vers + 1);
1052 if (vers > 1)
1053 return 1;
1054
1055 /*
1056 * Community.
1057 */
1058 if (!asn1_header_decode (&ctx, &end, &cls, &con, &tag))
1059 return 0;
1060 if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_OTS)
1061 return 0;
1062 if (!asn1_octets_decode(&ctx, end, &comm.data, &comm.len))
1063 return 0;
1064 if (debug > 1) {
1065 unsigned int i;
1066
1067 printk(KERN_DEBUG "bsalg: community: ");
1068 for (i = 0; i < comm.len; i++)
1069 printk("%c", comm.data[i]);
1070 printk("\n");
1071 }
1072 kfree(comm.data);
1073
1074 /*
1075 * PDU type
1076 */
1077 if (!asn1_header_decode(&ctx, &eoc, &cls, &con, &pdutype))
1078 return 0;
1079 if (cls != ASN1_CTX || con != ASN1_CON)
1080 return 0;
1081 if (debug > 1) {
1082 unsigned char *pdus[] = {
1083 [SNMP_PDU_GET] = "get",
1084 [SNMP_PDU_NEXT] = "get-next",
1085 [SNMP_PDU_RESPONSE] = "response",
1086 [SNMP_PDU_SET] = "set",
1087 [SNMP_PDU_TRAP1] = "trapv1",
1088 [SNMP_PDU_BULK] = "bulk",
1089 [SNMP_PDU_INFORM] = "inform",
1090 [SNMP_PDU_TRAP2] = "trapv2"
1091 };
1092
1093 if (pdutype > SNMP_PDU_TRAP2)
1094 printk(KERN_DEBUG "bsalg: bad pdu type %u\n", pdutype);
1095 else
1096 printk(KERN_DEBUG "bsalg: pdu: %s\n", pdus[pdutype]);
1097 }
1098 if (pdutype != SNMP_PDU_RESPONSE &&
1099 pdutype != SNMP_PDU_TRAP1 && pdutype != SNMP_PDU_TRAP2)
1100 return 1;
1101
1102 /*
1103 * Request header or v1 trap
1104 */
1105 if (pdutype == SNMP_PDU_TRAP1) {
1106 struct snmp_v1_trap trap;
1107 unsigned char ret = snmp_trap_decode(&ctx, &trap, map, check);
1108
1109 if (ret) {
1110 kfree(trap.id);
1111 kfree((unsigned long *)trap.ip_address);
1112 } else
1113 return ret;
1114
1115 } else {
1116 struct snmp_request req;
1117
1118 if (!snmp_request_decode(&ctx, &req))
1119 return 0;
1120
1121 if (debug > 1)
1122 printk(KERN_DEBUG "bsalg: request: id=0x%lx error_status=%u "
1123 "error_index=%u\n", req.id, req.error_status,
1124 req.error_index);
1125 }
1126
1127 /*
1128 * Loop through objects, look for IP addresses to mangle.
1129 */
1130 if (!asn1_header_decode(&ctx, &eoc, &cls, &con, &tag))
1131 return 0;
1132
1133 if (cls != ASN1_UNI || con != ASN1_CON || tag != ASN1_SEQ)
1134 return 0;
1135
1136 obj = kmalloc(sizeof(struct snmp_object), GFP_ATOMIC);
1137 if (obj == NULL) {
1138 if (net_ratelimit())
1139 printk(KERN_WARNING "OOM in bsalg(%d)\n", __LINE__);
1140 return 0;
1141 }
1142
1143 while (!asn1_eoc_decode(&ctx, eoc)) {
1144 unsigned int i;
1145
1146 if (!snmp_object_decode(&ctx, obj)) {
1147 if (*obj) {
1148 kfree((*obj)->id);
1149 kfree(*obj);
1150 }
1151 kfree(obj);
1152 return 0;
1153 }
1154
1155 if (debug > 1) {
1156 printk(KERN_DEBUG "bsalg: object: ");
1157 for (i = 0; i < (*obj)->id_len; i++) {
1158 if (i > 0)
1159 printk(".");
1160 printk("%lu", (*obj)->id[i]);
1161 }
1162 printk(": type=%u\n", (*obj)->type);
1163
1164 }
1165
1166 if ((*obj)->type == SNMP_IPADDR)
1167 mangle_address(ctx.begin, ctx.pointer - 4 , map, check);
1168
1169 kfree((*obj)->id);
1170 kfree(*obj);
1171 }
1172 kfree(obj);
1173
1174 if (!asn1_eoc_decode(&ctx, eoc))
1175 return 0;
1176
1177 return 1;
1178 }
1179
1180 /*****************************************************************************
1181 *
1182 * NAT routines.
1183 *
1184 *****************************************************************************/
1185
1186 /*
1187 * SNMP translation routine.
1188 */
1189 static int snmp_translate(struct nf_conn *ct,
1190 enum ip_conntrack_info ctinfo,
1191 struct sk_buff *skb)
1192 {
1193 struct iphdr *iph = ip_hdr(skb);
1194 struct udphdr *udph = (struct udphdr *)((__be32 *)iph + iph->ihl);
1195 u_int16_t udplen = ntohs(udph->len);
1196 u_int16_t paylen = udplen - sizeof(struct udphdr);
1197 int dir = CTINFO2DIR(ctinfo);
1198 struct oct1_map map;
1199
1200 /*
1201 * Determine mappping for application layer addresses based
1202 * on NAT manipulations for the packet.
1203 */
1204 if (dir == IP_CT_DIR_ORIGINAL) {
1205 /* SNAT traps */
1206 map.from = NOCT1(&ct->tuplehash[dir].tuple.src.u3.ip);
1207 map.to = NOCT1(&ct->tuplehash[!dir].tuple.dst.u3.ip);
1208 } else {
1209 /* DNAT replies */
1210 map.from = NOCT1(&ct->tuplehash[dir].tuple.src.u3.ip);
1211 map.to = NOCT1(&ct->tuplehash[!dir].tuple.dst.u3.ip);
1212 }
1213
1214 if (map.from == map.to)
1215 return NF_ACCEPT;
1216
1217 if (!snmp_parse_mangle((unsigned char *)udph + sizeof(struct udphdr),
1218 paylen, &map, &udph->check)) {
1219 if (net_ratelimit())
1220 printk(KERN_WARNING "bsalg: parser failed\n");
1221 return NF_DROP;
1222 }
1223 return NF_ACCEPT;
1224 }
1225
1226 /* We don't actually set up expectations, just adjust internal IP
1227 * addresses if this is being NATted */
1228 static int help(struct sk_buff *skb, unsigned int protoff,
1229 struct nf_conn *ct,
1230 enum ip_conntrack_info ctinfo)
1231 {
1232 int dir = CTINFO2DIR(ctinfo);
1233 unsigned int ret;
1234 struct iphdr *iph = ip_hdr(skb);
1235 struct udphdr *udph = (struct udphdr *)((u_int32_t *)iph + iph->ihl);
1236
1237 /* SNMP replies and originating SNMP traps get mangled */
1238 if (udph->source == htons(SNMP_PORT) && dir != IP_CT_DIR_REPLY)
1239 return NF_ACCEPT;
1240 if (udph->dest == htons(SNMP_TRAP_PORT) && dir != IP_CT_DIR_ORIGINAL)
1241 return NF_ACCEPT;
1242
1243 /* No NAT? */
1244 if (!(ct->status & IPS_NAT_MASK))
1245 return NF_ACCEPT;
1246
1247 /*
1248 * Make sure the packet length is ok. So far, we were only guaranteed
1249 * to have a valid length IP header plus 8 bytes, which means we have
1250 * enough room for a UDP header. Just verify the UDP length field so we
1251 * can mess around with the payload.
1252 */
1253 if (ntohs(udph->len) != skb->len - (iph->ihl << 2)) {
1254 if (net_ratelimit())
1255 printk(KERN_WARNING "SNMP: dropping malformed packet "
1256 "src=%u.%u.%u.%u dst=%u.%u.%u.%u\n",
1257 NIPQUAD(iph->saddr), NIPQUAD(iph->daddr));
1258 return NF_DROP;
1259 }
1260
1261 if (!skb_make_writable(skb, skb->len))
1262 return NF_DROP;
1263
1264 spin_lock_bh(&snmp_lock);
1265 ret = snmp_translate(ct, ctinfo, skb);
1266 spin_unlock_bh(&snmp_lock);
1267 return ret;
1268 }
1269
1270 static struct nf_conntrack_helper snmp_helper __read_mostly = {
1271 .max_expected = 0,
1272 .timeout = 180,
1273 .me = THIS_MODULE,
1274 .help = help,
1275 .name = "snmp",
1276 .tuple.src.l3num = AF_INET,
1277 .tuple.src.u.udp.port = __constant_htons(SNMP_PORT),
1278 .tuple.dst.protonum = IPPROTO_UDP,
1279 };
1280
1281 static struct nf_conntrack_helper snmp_trap_helper __read_mostly = {
1282 .max_expected = 0,
1283 .timeout = 180,
1284 .me = THIS_MODULE,
1285 .help = help,
1286 .name = "snmp_trap",
1287 .tuple.src.l3num = AF_INET,
1288 .tuple.src.u.udp.port = __constant_htons(SNMP_TRAP_PORT),
1289 .tuple.dst.protonum = IPPROTO_UDP,
1290 };
1291
1292 /*****************************************************************************
1293 *
1294 * Module stuff.
1295 *
1296 *****************************************************************************/
1297
1298 static int __init nf_nat_snmp_basic_init(void)
1299 {
1300 int ret = 0;
1301
1302 ret = nf_conntrack_helper_register(&snmp_helper);
1303 if (ret < 0)
1304 return ret;
1305 ret = nf_conntrack_helper_register(&snmp_trap_helper);
1306 if (ret < 0) {
1307 nf_conntrack_helper_unregister(&snmp_helper);
1308 return ret;
1309 }
1310 return ret;
1311 }
1312
1313 static void __exit nf_nat_snmp_basic_fini(void)
1314 {
1315 nf_conntrack_helper_unregister(&snmp_helper);
1316 nf_conntrack_helper_unregister(&snmp_trap_helper);
1317 }
1318
1319 module_init(nf_nat_snmp_basic_init);
1320 module_exit(nf_nat_snmp_basic_fini);
1321
1322 module_param(debug, int, 0600);
Linux kernel - Deliverables
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