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1 /*
2 * ip_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 * Updates:
43 * 2000-08-06: Convert to new helper API (Harald Welte).
44 *
45 */
46 #include <linux/config.h>
47 #include <linux/in.h>
48 #include <linux/module.h>
49 #include <linux/types.h>
50 #include <linux/kernel.h>
51 #include <linux/moduleparam.h>
52 #include <linux/netfilter_ipv4.h>
53 #include <linux/netfilter_ipv4/ip_nat.h>
54 #include <linux/netfilter_ipv4/ip_conntrack_helper.h>
55 #include <linux/netfilter_ipv4/ip_nat_helper.h>
56 #include <linux/ip.h>
57 #include <linux/udp.h>
58 #include <net/checksum.h>
59 #include <net/udp.h>
60 #include <asm/uaccess.h>
61
62 MODULE_LICENSE("GPL");
63 MODULE_AUTHOR("James Morris <jmorris@intercode.com.au>");
64 MODULE_DESCRIPTION("Basic SNMP Application Layer Gateway");
65
66 #define SNMP_PORT 161
67 #define SNMP_TRAP_PORT 162
68 #define NOCT1(n) (u_int8_t )((n) & 0xff)
69
70 static int debug;
71 static DEFINE_SPINLOCK(snmp_lock);
72
73 /*
74 * Application layer address mapping mimics the NAT mapping, but
75 * only for the first octet in this case (a more flexible system
76 * can be implemented if needed).
77 */
78 struct oct1_map
79 {
80 u_int8_t from;
81 u_int8_t to;
82 };
83
84
85 /*****************************************************************************
86 *
87 * Basic ASN.1 decoding routines (gxsnmp author Dirk Wisse)
88 *
89 *****************************************************************************/
90
91 /* Class */
92 #define ASN1_UNI 0 /* Universal */
93 #define ASN1_APL 1 /* Application */
94 #define ASN1_CTX 2 /* Context */
95 #define ASN1_PRV 3 /* Private */
96
97 /* Tag */
98 #define ASN1_EOC 0 /* End Of Contents */
99 #define ASN1_BOL 1 /* Boolean */
100 #define ASN1_INT 2 /* Integer */
101 #define ASN1_BTS 3 /* Bit String */
102 #define ASN1_OTS 4 /* Octet String */
103 #define ASN1_NUL 5 /* Null */
104 #define ASN1_OJI 6 /* Object Identifier */
105 #define ASN1_OJD 7 /* Object Description */
106 #define ASN1_EXT 8 /* External */
107 #define ASN1_SEQ 16 /* Sequence */
108 #define ASN1_SET 17 /* Set */
109 #define ASN1_NUMSTR 18 /* Numerical String */
110 #define ASN1_PRNSTR 19 /* Printable String */
111 #define ASN1_TEXSTR 20 /* Teletext String */
112 #define ASN1_VIDSTR 21 /* Video String */
113 #define ASN1_IA5STR 22 /* IA5 String */
114 #define ASN1_UNITIM 23 /* Universal Time */
115 #define ASN1_GENTIM 24 /* General Time */
116 #define ASN1_GRASTR 25 /* Graphical String */
117 #define ASN1_VISSTR 26 /* Visible String */
118 #define ASN1_GENSTR 27 /* General String */
119
120 /* Primitive / Constructed methods*/
121 #define ASN1_PRI 0 /* Primitive */
122 #define ASN1_CON 1 /* Constructed */
123
124 /*
125 * Error codes.
126 */
127 #define ASN1_ERR_NOERROR 0
128 #define ASN1_ERR_DEC_EMPTY 2
129 #define ASN1_ERR_DEC_EOC_MISMATCH 3
130 #define ASN1_ERR_DEC_LENGTH_MISMATCH 4
131 #define ASN1_ERR_DEC_BADVALUE 5
132
133 /*
134 * ASN.1 context.
135 */
136 struct asn1_ctx
137 {
138 int error; /* Error condition */
139 unsigned char *pointer; /* Octet just to be decoded */
140 unsigned char *begin; /* First octet */
141 unsigned char *end; /* Octet after last octet */
142 };
143
144 /*
145 * Octet string (not null terminated)
146 */
147 struct asn1_octstr
148 {
149 unsigned char *data;
150 unsigned int len;
151 };
152
153 static void asn1_open(struct asn1_ctx *ctx,
154 unsigned char *buf,
155 unsigned int len)
156 {
157 ctx->begin = buf;
158 ctx->end = buf + len;
159 ctx->pointer = buf;
160 ctx->error = ASN1_ERR_NOERROR;
161 }
162
163 static unsigned char asn1_octet_decode(struct asn1_ctx *ctx, unsigned char *ch)
164 {
165 if (ctx->pointer >= ctx->end) {
166 ctx->error = ASN1_ERR_DEC_EMPTY;
167 return 0;
168 }
169 *ch = *(ctx->pointer)++;
170 return 1;
171 }
172
173 static unsigned char asn1_tag_decode(struct asn1_ctx *ctx, unsigned int *tag)
174 {
175 unsigned char ch;
176
177 *tag = 0;
178
179 do
180 {
181 if (!asn1_octet_decode(ctx, &ch))
182 return 0;
183 *tag <<= 7;
184 *tag |= ch & 0x7F;
185 } while ((ch & 0x80) == 0x80);
186 return 1;
187 }
188
189 static unsigned char asn1_id_decode(struct asn1_ctx *ctx,
190 unsigned int *cls,
191 unsigned int *con,
192 unsigned int *tag)
193 {
194 unsigned char ch;
195
196 if (!asn1_octet_decode(ctx, &ch))
197 return 0;
198
199 *cls = (ch & 0xC0) >> 6;
200 *con = (ch & 0x20) >> 5;
201 *tag = (ch & 0x1F);
202
203 if (*tag == 0x1F) {
204 if (!asn1_tag_decode(ctx, tag))
205 return 0;
206 }
207 return 1;
208 }
209
210 static unsigned char asn1_length_decode(struct asn1_ctx *ctx,
211 unsigned int *def,
212 unsigned int *len)
213 {
214 unsigned char ch, cnt;
215
216 if (!asn1_octet_decode(ctx, &ch))
217 return 0;
218
219 if (ch == 0x80)
220 *def = 0;
221 else {
222 *def = 1;
223
224 if (ch < 0x80)
225 *len = ch;
226 else {
227 cnt = (unsigned char) (ch & 0x7F);
228 *len = 0;
229
230 while (cnt > 0) {
231 if (!asn1_octet_decode(ctx, &ch))
232 return 0;
233 *len <<= 8;
234 *len |= ch;
235 cnt--;
236 }
237 }
238 }
239 return 1;
240 }
241
242 static unsigned char asn1_header_decode(struct asn1_ctx *ctx,
243 unsigned char **eoc,
244 unsigned int *cls,
245 unsigned int *con,
246 unsigned int *tag)
247 {
248 unsigned int def, len;
249
250 if (!asn1_id_decode(ctx, cls, con, tag))
251 return 0;
252
253 def = len = 0;
254 if (!asn1_length_decode(ctx, &def, &len))
255 return 0;
256
257 if (def)
258 *eoc = ctx->pointer + len;
259 else
260 *eoc = NULL;
261 return 1;
262 }
263
264 static unsigned char asn1_eoc_decode(struct asn1_ctx *ctx, unsigned char *eoc)
265 {
266 unsigned char ch;
267
268 if (eoc == 0) {
269 if (!asn1_octet_decode(ctx, &ch))
270 return 0;
271
272 if (ch != 0x00) {
273 ctx->error = ASN1_ERR_DEC_EOC_MISMATCH;
274 return 0;
275 }
276
277 if (!asn1_octet_decode(ctx, &ch))
278 return 0;
279
280 if (ch != 0x00) {
281 ctx->error = ASN1_ERR_DEC_EOC_MISMATCH;
282 return 0;
283 }
284 return 1;
285 } else {
286 if (ctx->pointer != eoc) {
287 ctx->error = ASN1_ERR_DEC_LENGTH_MISMATCH;
288 return 0;
289 }
290 return 1;
291 }
292 }
293
294 static unsigned char asn1_null_decode(struct asn1_ctx *ctx, unsigned char *eoc)
295 {
296 ctx->pointer = eoc;
297 return 1;
298 }
299
300 static unsigned char asn1_long_decode(struct asn1_ctx *ctx,
301 unsigned char *eoc,
302 long *integer)
303 {
304 unsigned char ch;
305 unsigned int len;
306
307 if (!asn1_octet_decode(ctx, &ch))
308 return 0;
309
310 *integer = (signed char) ch;
311 len = 1;
312
313 while (ctx->pointer < eoc) {
314 if (++len > sizeof (long)) {
315 ctx->error = ASN1_ERR_DEC_BADVALUE;
316 return 0;
317 }
318
319 if (!asn1_octet_decode(ctx, &ch))
320 return 0;
321
322 *integer <<= 8;
323 *integer |= ch;
324 }
325 return 1;
326 }
327
328 static unsigned char asn1_uint_decode(struct asn1_ctx *ctx,
329 unsigned char *eoc,
330 unsigned int *integer)
331 {
332 unsigned char ch;
333 unsigned int len;
334
335 if (!asn1_octet_decode(ctx, &ch))
336 return 0;
337
338 *integer = ch;
339 if (ch == 0) len = 0;
340 else len = 1;
341
342 while (ctx->pointer < eoc) {
343 if (++len > sizeof (unsigned int)) {
344 ctx->error = ASN1_ERR_DEC_BADVALUE;
345 return 0;
346 }
347
348 if (!asn1_octet_decode(ctx, &ch))
349 return 0;
350
351 *integer <<= 8;
352 *integer |= ch;
353 }
354 return 1;
355 }
356
357 static unsigned char asn1_ulong_decode(struct asn1_ctx *ctx,
358 unsigned char *eoc,
359 unsigned long *integer)
360 {
361 unsigned char ch;
362 unsigned int len;
363
364 if (!asn1_octet_decode(ctx, &ch))
365 return 0;
366
367 *integer = ch;
368 if (ch == 0) len = 0;
369 else len = 1;
370
371 while (ctx->pointer < eoc) {
372 if (++len > sizeof (unsigned long)) {
373 ctx->error = ASN1_ERR_DEC_BADVALUE;
374 return 0;
375 }
376
377 if (!asn1_octet_decode(ctx, &ch))
378 return 0;
379
380 *integer <<= 8;
381 *integer |= ch;
382 }
383 return 1;
384 }
385
386 static unsigned char asn1_octets_decode(struct asn1_ctx *ctx,
387 unsigned char *eoc,
388 unsigned char **octets,
389 unsigned int *len)
390 {
391 unsigned char *ptr;
392
393 *len = 0;
394
395 *octets = kmalloc(eoc - ctx->pointer, GFP_ATOMIC);
396 if (*octets == NULL) {
397 if (net_ratelimit())
398 printk("OOM in bsalg (%d)\n", __LINE__);
399 return 0;
400 }
401
402 ptr = *octets;
403 while (ctx->pointer < eoc) {
404 if (!asn1_octet_decode(ctx, (unsigned char *)ptr++)) {
405 kfree(*octets);
406 *octets = NULL;
407 return 0;
408 }
409 (*len)++;
410 }
411 return 1;
412 }
413
414 static unsigned char asn1_subid_decode(struct asn1_ctx *ctx,
415 unsigned long *subid)
416 {
417 unsigned char ch;
418
419 *subid = 0;
420
421 do {
422 if (!asn1_octet_decode(ctx, &ch))
423 return 0;
424
425 *subid <<= 7;
426 *subid |= ch & 0x7F;
427 } while ((ch & 0x80) == 0x80);
428 return 1;
429 }
430
431 static unsigned char asn1_oid_decode(struct asn1_ctx *ctx,
432 unsigned char *eoc,
433 unsigned long **oid,
434 unsigned int *len)
435 {
436 unsigned long subid;
437 unsigned int size;
438 unsigned long *optr;
439
440 size = eoc - ctx->pointer + 1;
441 *oid = kmalloc(size * sizeof(unsigned long), GFP_ATOMIC);
442 if (*oid == NULL) {
443 if (net_ratelimit())
444 printk("OOM in bsalg (%d)\n", __LINE__);
445 return 0;
446 }
447
448 optr = *oid;
449
450 if (!asn1_subid_decode(ctx, &subid)) {
451 kfree(*oid);
452 *oid = NULL;
453 return 0;
454 }
455
456 if (subid < 40) {
457 optr [0] = 0;
458 optr [1] = subid;
459 } else if (subid < 80) {
460 optr [0] = 1;
461 optr [1] = subid - 40;
462 } else {
463 optr [0] = 2;
464 optr [1] = subid - 80;
465 }
466
467 *len = 2;
468 optr += 2;
469
470 while (ctx->pointer < eoc) {
471 if (++(*len) > size) {
472 ctx->error = ASN1_ERR_DEC_BADVALUE;
473 kfree(*oid);
474 *oid = NULL;
475 return 0;
476 }
477
478 if (!asn1_subid_decode(ctx, optr++)) {
479 kfree(*oid);
480 *oid = NULL;
481 return 0;
482 }
483 }
484 return 1;
485 }
486
487 /*****************************************************************************
488 *
489 * SNMP decoding routines (gxsnmp author Dirk Wisse)
490 *
491 *****************************************************************************/
492
493 /* SNMP Versions */
494 #define SNMP_V1 0
495 #define SNMP_V2C 1
496 #define SNMP_V2 2
497 #define SNMP_V3 3
498
499 /* Default Sizes */
500 #define SNMP_SIZE_COMM 256
501 #define SNMP_SIZE_OBJECTID 128
502 #define SNMP_SIZE_BUFCHR 256
503 #define SNMP_SIZE_BUFINT 128
504 #define SNMP_SIZE_SMALLOBJECTID 16
505
506 /* Requests */
507 #define SNMP_PDU_GET 0
508 #define SNMP_PDU_NEXT 1
509 #define SNMP_PDU_RESPONSE 2
510 #define SNMP_PDU_SET 3
511 #define SNMP_PDU_TRAP1 4
512 #define SNMP_PDU_BULK 5
513 #define SNMP_PDU_INFORM 6
514 #define SNMP_PDU_TRAP2 7
515
516 /* Errors */
517 #define SNMP_NOERROR 0
518 #define SNMP_TOOBIG 1
519 #define SNMP_NOSUCHNAME 2
520 #define SNMP_BADVALUE 3
521 #define SNMP_READONLY 4
522 #define SNMP_GENERROR 5
523 #define SNMP_NOACCESS 6
524 #define SNMP_WRONGTYPE 7
525 #define SNMP_WRONGLENGTH 8
526 #define SNMP_WRONGENCODING 9
527 #define SNMP_WRONGVALUE 10
528 #define SNMP_NOCREATION 11
529 #define SNMP_INCONSISTENTVALUE 12
530 #define SNMP_RESOURCEUNAVAILABLE 13
531 #define SNMP_COMMITFAILED 14
532 #define SNMP_UNDOFAILED 15
533 #define SNMP_AUTHORIZATIONERROR 16
534 #define SNMP_NOTWRITABLE 17
535 #define SNMP_INCONSISTENTNAME 18
536
537 /* General SNMP V1 Traps */
538 #define SNMP_TRAP_COLDSTART 0
539 #define SNMP_TRAP_WARMSTART 1
540 #define SNMP_TRAP_LINKDOWN 2
541 #define SNMP_TRAP_LINKUP 3
542 #define SNMP_TRAP_AUTFAILURE 4
543 #define SNMP_TRAP_EQPNEIGHBORLOSS 5
544 #define SNMP_TRAP_ENTSPECIFIC 6
545
546 /* SNMPv1 Types */
547 #define SNMP_NULL 0
548 #define SNMP_INTEGER 1 /* l */
549 #define SNMP_OCTETSTR 2 /* c */
550 #define SNMP_DISPLAYSTR 2 /* c */
551 #define SNMP_OBJECTID 3 /* ul */
552 #define SNMP_IPADDR 4 /* uc */
553 #define SNMP_COUNTER 5 /* ul */
554 #define SNMP_GAUGE 6 /* ul */
555 #define SNMP_TIMETICKS 7 /* ul */
556 #define SNMP_OPAQUE 8 /* c */
557
558 /* Additional SNMPv2 Types */
559 #define SNMP_UINTEGER 5 /* ul */
560 #define SNMP_BITSTR 9 /* uc */
561 #define SNMP_NSAP 10 /* uc */
562 #define SNMP_COUNTER64 11 /* ul */
563 #define SNMP_NOSUCHOBJECT 12
564 #define SNMP_NOSUCHINSTANCE 13
565 #define SNMP_ENDOFMIBVIEW 14
566
567 union snmp_syntax
568 {
569 unsigned char uc[0]; /* 8 bit unsigned */
570 char c[0]; /* 8 bit signed */
571 unsigned long ul[0]; /* 32 bit unsigned */
572 long l[0]; /* 32 bit signed */
573 };
574
575 struct snmp_object
576 {
577 unsigned long *id;
578 unsigned int id_len;
579 unsigned short type;
580 unsigned int syntax_len;
581 union snmp_syntax syntax;
582 };
583
584 struct snmp_request
585 {
586 unsigned long id;
587 unsigned int error_status;
588 unsigned int error_index;
589 };
590
591 struct snmp_v1_trap
592 {
593 unsigned long *id;
594 unsigned int id_len;
595 unsigned long ip_address; /* pointer */
596 unsigned int general;
597 unsigned int specific;
598 unsigned long time;
599 };
600
601 /* SNMP types */
602 #define SNMP_IPA 0
603 #define SNMP_CNT 1
604 #define SNMP_GGE 2
605 #define SNMP_TIT 3
606 #define SNMP_OPQ 4
607 #define SNMP_C64 6
608
609 /* SNMP errors */
610 #define SERR_NSO 0
611 #define SERR_NSI 1
612 #define SERR_EOM 2
613
614 static inline void mangle_address(unsigned char *begin,
615 unsigned char *addr,
616 const struct oct1_map *map,
617 u_int16_t *check);
618 struct snmp_cnv
619 {
620 unsigned int class;
621 unsigned int tag;
622 int syntax;
623 };
624
625 static struct snmp_cnv snmp_conv [] =
626 {
627 {ASN1_UNI, ASN1_NUL, SNMP_NULL},
628 {ASN1_UNI, ASN1_INT, SNMP_INTEGER},
629 {ASN1_UNI, ASN1_OTS, SNMP_OCTETSTR},
630 {ASN1_UNI, ASN1_OTS, SNMP_DISPLAYSTR},
631 {ASN1_UNI, ASN1_OJI, SNMP_OBJECTID},
632 {ASN1_APL, SNMP_IPA, SNMP_IPADDR},
633 {ASN1_APL, SNMP_CNT, SNMP_COUNTER}, /* Counter32 */
634 {ASN1_APL, SNMP_GGE, SNMP_GAUGE}, /* Gauge32 == Unsigned32 */
635 {ASN1_APL, SNMP_TIT, SNMP_TIMETICKS},
636 {ASN1_APL, SNMP_OPQ, SNMP_OPAQUE},
637
638 /* SNMPv2 data types and errors */
639 {ASN1_UNI, ASN1_BTS, SNMP_BITSTR},
640 {ASN1_APL, SNMP_C64, SNMP_COUNTER64},
641 {ASN1_CTX, SERR_NSO, SNMP_NOSUCHOBJECT},
642 {ASN1_CTX, SERR_NSI, SNMP_NOSUCHINSTANCE},
643 {ASN1_CTX, SERR_EOM, SNMP_ENDOFMIBVIEW},
644 {0, 0, -1}
645 };
646
647 static unsigned char snmp_tag_cls2syntax(unsigned int tag,
648 unsigned int cls,
649 unsigned short *syntax)
650 {
651 struct snmp_cnv *cnv;
652
653 cnv = snmp_conv;
654
655 while (cnv->syntax != -1) {
656 if (cnv->tag == tag && cnv->class == cls) {
657 *syntax = cnv->syntax;
658 return 1;
659 }
660 cnv++;
661 }
662 return 0;
663 }
664
665 static unsigned char snmp_object_decode(struct asn1_ctx *ctx,
666 struct snmp_object **obj)
667 {
668 unsigned int cls, con, tag, len, idlen;
669 unsigned short type;
670 unsigned char *eoc, *end, *p;
671 unsigned long *lp, *id;
672 unsigned long ul;
673 long l;
674
675 *obj = NULL;
676 id = NULL;
677
678 if (!asn1_header_decode(ctx, &eoc, &cls, &con, &tag))
679 return 0;
680
681 if (cls != ASN1_UNI || con != ASN1_CON || tag != ASN1_SEQ)
682 return 0;
683
684 if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
685 return 0;
686
687 if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_OJI)
688 return 0;
689
690 if (!asn1_oid_decode(ctx, end, &id, &idlen))
691 return 0;
692
693 if (!asn1_header_decode(ctx, &end, &cls, &con, &tag)) {
694 kfree(id);
695 return 0;
696 }
697
698 if (con != ASN1_PRI) {
699 kfree(id);
700 return 0;
701 }
702
703 type = 0;
704 if (!snmp_tag_cls2syntax(tag, cls, &type)) {
705 kfree(id);
706 return 0;
707 }
708
709 l = 0;
710 switch (type) {
711 case SNMP_INTEGER:
712 len = sizeof(long);
713 if (!asn1_long_decode(ctx, end, &l)) {
714 kfree(id);
715 return 0;
716 }
717 *obj = kmalloc(sizeof(struct snmp_object) + len,
718 GFP_ATOMIC);
719 if (*obj == NULL) {
720 kfree(id);
721 if (net_ratelimit())
722 printk("OOM in bsalg (%d)\n", __LINE__);
723 return 0;
724 }
725 (*obj)->syntax.l[0] = l;
726 break;
727 case SNMP_OCTETSTR:
728 case SNMP_OPAQUE:
729 if (!asn1_octets_decode(ctx, end, &p, &len)) {
730 kfree(id);
731 return 0;
732 }
733 *obj = kmalloc(sizeof(struct snmp_object) + len,
734 GFP_ATOMIC);
735 if (*obj == NULL) {
736 kfree(id);
737 if (net_ratelimit())
738 printk("OOM in bsalg (%d)\n", __LINE__);
739 return 0;
740 }
741 memcpy((*obj)->syntax.c, p, len);
742 kfree(p);
743 break;
744 case SNMP_NULL:
745 case SNMP_NOSUCHOBJECT:
746 case SNMP_NOSUCHINSTANCE:
747 case SNMP_ENDOFMIBVIEW:
748 len = 0;
749 *obj = kmalloc(sizeof(struct snmp_object), GFP_ATOMIC);
750 if (*obj == NULL) {
751 kfree(id);
752 if (net_ratelimit())
753 printk("OOM in bsalg (%d)\n", __LINE__);
754 return 0;
755 }
756 if (!asn1_null_decode(ctx, end)) {
757 kfree(id);
758 kfree(*obj);
759 *obj = NULL;
760 return 0;
761 }
762 break;
763 case SNMP_OBJECTID:
764 if (!asn1_oid_decode(ctx, end, (unsigned long **)&lp, &len)) {
765 kfree(id);
766 return 0;
767 }
768 len *= sizeof(unsigned long);
769 *obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
770 if (*obj == NULL) {
771 kfree(id);
772 if (net_ratelimit())
773 printk("OOM in bsalg (%d)\n", __LINE__);
774 return 0;
775 }
776 memcpy((*obj)->syntax.ul, lp, len);
777 kfree(lp);
778 break;
779 case SNMP_IPADDR:
780 if (!asn1_octets_decode(ctx, end, &p, &len)) {
781 kfree(id);
782 return 0;
783 }
784 if (len != 4) {
785 kfree(p);
786 kfree(id);
787 return 0;
788 }
789 *obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
790 if (*obj == NULL) {
791 kfree(p);
792 kfree(id);
793 if (net_ratelimit())
794 printk("OOM in bsalg (%d)\n", __LINE__);
795 return 0;
796 }
797 memcpy((*obj)->syntax.uc, p, len);
798 kfree(p);
799 break;
800 case SNMP_COUNTER:
801 case SNMP_GAUGE:
802 case SNMP_TIMETICKS:
803 len = sizeof(unsigned long);
804 if (!asn1_ulong_decode(ctx, end, &ul)) {
805 kfree(id);
806 return 0;
807 }
808 *obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
809 if (*obj == NULL) {
810 kfree(id);
811 if (net_ratelimit())
812 printk("OOM in bsalg (%d)\n", __LINE__);
813 return 0;
814 }
815 (*obj)->syntax.ul[0] = ul;
816 break;
817 default:
818 kfree(id);
819 return 0;
820 }
821
822 (*obj)->syntax_len = len;
823 (*obj)->type = type;
824 (*obj)->id = id;
825 (*obj)->id_len = idlen;
826
827 if (!asn1_eoc_decode(ctx, eoc)) {
828 kfree(id);
829 kfree(*obj);
830 *obj = NULL;
831 return 0;
832 }
833 return 1;
834 }
835
836 static unsigned char snmp_request_decode(struct asn1_ctx *ctx,
837 struct snmp_request *request)
838 {
839 unsigned int cls, con, tag;
840 unsigned char *end;
841
842 if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
843 return 0;
844
845 if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
846 return 0;
847
848 if (!asn1_ulong_decode(ctx, end, &request->id))
849 return 0;
850
851 if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
852 return 0;
853
854 if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
855 return 0;
856
857 if (!asn1_uint_decode(ctx, end, &request->error_status))
858 return 0;
859
860 if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
861 return 0;
862
863 if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
864 return 0;
865
866 if (!asn1_uint_decode(ctx, end, &request->error_index))
867 return 0;
868
869 return 1;
870 }
871
872 /*
873 * Fast checksum update for possibly oddly-aligned UDP byte, from the
874 * code example in the draft.
875 */
876 static void fast_csum(unsigned char *csum,
877 const unsigned char *optr,
878 const unsigned char *nptr,
879 int odd)
880 {
881 long x, old, new;
882
883 x = csum[0] * 256 + csum[1];
884
885 x =~ x & 0xFFFF;
886
887 if (odd) old = optr[0] * 256;
888 else old = optr[0];
889
890 x -= old & 0xFFFF;
891 if (x <= 0) {
892 x--;
893 x &= 0xFFFF;
894 }
895
896 if (odd) new = nptr[0] * 256;
897 else new = nptr[0];
898
899 x += new & 0xFFFF;
900 if (x & 0x10000) {
901 x++;
902 x &= 0xFFFF;
903 }
904
905 x =~ x & 0xFFFF;
906 csum[0] = x / 256;
907 csum[1] = x & 0xFF;
908 }
909
910 /*
911 * Mangle IP address.
912 * - begin points to the start of the snmp messgae
913 * - addr points to the start of the address
914 */
915 static inline void mangle_address(unsigned char *begin,
916 unsigned char *addr,
917 const struct oct1_map *map,
918 u_int16_t *check)
919 {
920 if (map->from == NOCT1(*addr)) {
921 u_int32_t old;
922
923 if (debug)
924 memcpy(&old, (unsigned char *)addr, sizeof(old));
925
926 *addr = map->to;
927
928 /* Update UDP checksum if being used */
929 if (*check) {
930 unsigned char odd = !((addr - begin) % 2);
931
932 fast_csum((unsigned char *)check,
933 &map->from, &map->to, odd);
934
935 }
936
937 if (debug)
938 printk(KERN_DEBUG "bsalg: mapped %u.%u.%u.%u to "
939 "%u.%u.%u.%u\n", NIPQUAD(old), NIPQUAD(*addr));
940 }
941 }
942
943 static unsigned char snmp_trap_decode(struct asn1_ctx *ctx,
944 struct snmp_v1_trap *trap,
945 const struct oct1_map *map,
946 u_int16_t *check)
947 {
948 unsigned int cls, con, tag, len;
949 unsigned char *end;
950
951 if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
952 return 0;
953
954 if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_OJI)
955 return 0;
956
957 if (!asn1_oid_decode(ctx, end, &trap->id, &trap->id_len))
958 return 0;
959
960 if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
961 goto err_id_free;
962
963 if (!((cls == ASN1_APL && con == ASN1_PRI && tag == SNMP_IPA) ||
964 (cls == ASN1_UNI && con == ASN1_PRI && tag == ASN1_OTS)))
965 goto err_id_free;
966
967 if (!asn1_octets_decode(ctx, end, (unsigned char **)&trap->ip_address, &len))
968 goto err_id_free;
969
970 /* IPv4 only */
971 if (len != 4)
972 goto err_addr_free;
973
974 mangle_address(ctx->begin, ctx->pointer - 4, map, check);
975
976 if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
977 goto err_addr_free;
978
979 if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
980 goto err_addr_free;
981
982 if (!asn1_uint_decode(ctx, end, &trap->general))
983 goto err_addr_free;
984
985 if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
986 goto err_addr_free;
987
988 if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
989 goto err_addr_free;
990
991 if (!asn1_uint_decode(ctx, end, &trap->specific))
992 goto err_addr_free;
993
994 if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
995 goto err_addr_free;
996
997 if (!((cls == ASN1_APL && con == ASN1_PRI && tag == SNMP_TIT) ||
998 (cls == ASN1_UNI && con == ASN1_PRI && tag == ASN1_INT)))
999 goto err_addr_free;
1000
1001 if (!asn1_ulong_decode(ctx, end, &trap->time))
1002 goto err_addr_free;
1003
1004 return 1;
1005
1006 err_id_free:
1007 kfree(trap->id);
1008
1009 err_addr_free:
1010 kfree((unsigned long *)trap->ip_address);
1011
1012 return 0;
1013 }
1014
1015 /*****************************************************************************
1016 *
1017 * Misc. routines
1018 *
1019 *****************************************************************************/
1020
1021 static void hex_dump(unsigned char *buf, size_t len)
1022 {
1023 size_t i;
1024
1025 for (i = 0; i < len; i++) {
1026 if (i && !(i % 16))
1027 printk("\n");
1028 printk("%02x ", *(buf + i));
1029 }
1030 printk("\n");
1031 }
1032
1033 /*
1034 * Parse and mangle SNMP message according to mapping.
1035 * (And this is the fucking 'basic' method).
1036 */
1037 static int snmp_parse_mangle(unsigned char *msg,
1038 u_int16_t len,
1039 const struct oct1_map *map,
1040 u_int16_t *check)
1041 {
1042 unsigned char *eoc, *end;
1043 unsigned int cls, con, tag, vers, pdutype;
1044 struct asn1_ctx ctx;
1045 struct asn1_octstr comm;
1046 struct snmp_object **obj;
1047
1048 if (debug > 1)
1049 hex_dump(msg, len);
1050
1051 asn1_open(&ctx, msg, len);
1052
1053 /*
1054 * Start of SNMP message.
1055 */
1056 if (!asn1_header_decode(&ctx, &eoc, &cls, &con, &tag))
1057 return 0;
1058 if (cls != ASN1_UNI || con != ASN1_CON || tag != ASN1_SEQ)
1059 return 0;
1060
1061 /*
1062 * Version 1 or 2 handled.
1063 */
1064 if (!asn1_header_decode(&ctx, &end, &cls, &con, &tag))
1065 return 0;
1066 if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
1067 return 0;
1068 if (!asn1_uint_decode (&ctx, end, &vers))
1069 return 0;
1070 if (debug > 1)
1071 printk(KERN_DEBUG "bsalg: snmp version: %u\n", vers + 1);
1072 if (vers > 1)
1073 return 1;
1074
1075 /*
1076 * Community.
1077 */
1078 if (!asn1_header_decode (&ctx, &end, &cls, &con, &tag))
1079 return 0;
1080 if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_OTS)
1081 return 0;
1082 if (!asn1_octets_decode(&ctx, end, &comm.data, &comm.len))
1083 return 0;
1084 if (debug > 1) {
1085 unsigned int i;
1086
1087 printk(KERN_DEBUG "bsalg: community: ");
1088 for (i = 0; i < comm.len; i++)
1089 printk("%c", comm.data[i]);
1090 printk("\n");
1091 }
1092 kfree(comm.data);
1093
1094 /*
1095 * PDU type
1096 */
1097 if (!asn1_header_decode(&ctx, &eoc, &cls, &con, &pdutype))
1098 return 0;
1099 if (cls != ASN1_CTX || con != ASN1_CON)
1100 return 0;
1101 if (debug > 1) {
1102 unsigned char *pdus[] = {
1103 [SNMP_PDU_GET] = "get",
1104 [SNMP_PDU_NEXT] = "get-next",
1105 [SNMP_PDU_RESPONSE] = "response",
1106 [SNMP_PDU_SET] = "set",
1107 [SNMP_PDU_TRAP1] = "trapv1",
1108 [SNMP_PDU_BULK] = "bulk",
1109 [SNMP_PDU_INFORM] = "inform",
1110 [SNMP_PDU_TRAP2] = "trapv2"
1111 };
1112
1113 if (pdutype > SNMP_PDU_TRAP2)
1114 printk(KERN_DEBUG "bsalg: bad pdu type %u\n", pdutype);
1115 else
1116 printk(KERN_DEBUG "bsalg: pdu: %s\n", pdus[pdutype]);
1117 }
1118 if (pdutype != SNMP_PDU_RESPONSE &&
1119 pdutype != SNMP_PDU_TRAP1 && pdutype != SNMP_PDU_TRAP2)
1120 return 1;
1121
1122 /*
1123 * Request header or v1 trap
1124 */
1125 if (pdutype == SNMP_PDU_TRAP1) {
1126 struct snmp_v1_trap trap;
1127 unsigned char ret = snmp_trap_decode(&ctx, &trap, map, check);
1128
1129 /* Discard trap allocations regardless */
1130 kfree(trap.id);
1131 kfree((unsigned long *)trap.ip_address);
1132
1133 if (!ret)
1134 return ret;
1135
1136 } else {
1137 struct snmp_request req;
1138
1139 if (!snmp_request_decode(&ctx, &req))
1140 return 0;
1141
1142 if (debug > 1)
1143 printk(KERN_DEBUG "bsalg: request: id=0x%lx error_status=%u "
1144 "error_index=%u\n", req.id, req.error_status,
1145 req.error_index);
1146 }
1147
1148 /*
1149 * Loop through objects, look for IP addresses to mangle.
1150 */
1151 if (!asn1_header_decode(&ctx, &eoc, &cls, &con, &tag))
1152 return 0;
1153
1154 if (cls != ASN1_UNI || con != ASN1_CON || tag != ASN1_SEQ)
1155 return 0;
1156
1157 obj = kmalloc(sizeof(struct snmp_object), GFP_ATOMIC);
1158 if (obj == NULL) {
1159 if (net_ratelimit())
1160 printk(KERN_WARNING "OOM in bsalg(%d)\n", __LINE__);
1161 return 0;
1162 }
1163
1164 while (!asn1_eoc_decode(&ctx, eoc)) {
1165 unsigned int i;
1166
1167 if (!snmp_object_decode(&ctx, obj)) {
1168 if (*obj) {
1169 kfree((*obj)->id);
1170 kfree(*obj);
1171 }
1172 kfree(obj);
1173 return 0;
1174 }
1175
1176 if (debug > 1) {
1177 printk(KERN_DEBUG "bsalg: object: ");
1178 for (i = 0; i < (*obj)->id_len; i++) {
1179 if (i > 0)
1180 printk(".");
1181 printk("%lu", (*obj)->id[i]);
1182 }
1183 printk(": type=%u\n", (*obj)->type);
1184
1185 }
1186
1187 if ((*obj)->type == SNMP_IPADDR)
1188 mangle_address(ctx.begin, ctx.pointer - 4 , map, check);
1189
1190 kfree((*obj)->id);
1191 kfree(*obj);
1192 }
1193 kfree(obj);
1194
1195 if (!asn1_eoc_decode(&ctx, eoc))
1196 return 0;
1197
1198 return 1;
1199 }
1200
1201 /*****************************************************************************
1202 *
1203 * NAT routines.
1204 *
1205 *****************************************************************************/
1206
1207 /*
1208 * SNMP translation routine.
1209 */
1210 static int snmp_translate(struct ip_conntrack *ct,
1211 enum ip_conntrack_info ctinfo,
1212 struct sk_buff **pskb)
1213 {
1214 struct iphdr *iph = (*pskb)->nh.iph;
1215 struct udphdr *udph = (struct udphdr *)((u_int32_t *)iph + iph->ihl);
1216 u_int16_t udplen = ntohs(udph->len);
1217 u_int16_t paylen = udplen - sizeof(struct udphdr);
1218 int dir = CTINFO2DIR(ctinfo);
1219 struct oct1_map map;
1220
1221 /*
1222 * Determine mappping for application layer addresses based
1223 * on NAT manipulations for the packet.
1224 */
1225 if (dir == IP_CT_DIR_ORIGINAL) {
1226 /* SNAT traps */
1227 map.from = NOCT1(ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.ip);
1228 map.to = NOCT1(ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.ip);
1229 } else {
1230 /* DNAT replies */
1231 map.from = NOCT1(ct->tuplehash[IP_CT_DIR_REPLY].tuple.src.ip);
1232 map.to = NOCT1(ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.dst.ip);
1233 }
1234
1235 if (map.from == map.to)
1236 return NF_ACCEPT;
1237
1238 if (!snmp_parse_mangle((unsigned char *)udph + sizeof(struct udphdr),
1239 paylen, &map, &udph->check)) {
1240 if (net_ratelimit())
1241 printk(KERN_WARNING "bsalg: parser failed\n");
1242 return NF_DROP;
1243 }
1244 return NF_ACCEPT;
1245 }
1246
1247 /* We don't actually set up expectations, just adjust internal IP
1248 * addresses if this is being NATted */
1249 static int help(struct sk_buff **pskb,
1250 struct ip_conntrack *ct,
1251 enum ip_conntrack_info ctinfo)
1252 {
1253 int dir = CTINFO2DIR(ctinfo);
1254 unsigned int ret;
1255 struct iphdr *iph = (*pskb)->nh.iph;
1256 struct udphdr *udph = (struct udphdr *)((u_int32_t *)iph + iph->ihl);
1257
1258 /* SNMP replies and originating SNMP traps get mangled */
1259 if (udph->source == ntohs(SNMP_PORT) && dir != IP_CT_DIR_REPLY)
1260 return NF_ACCEPT;
1261 if (udph->dest == ntohs(SNMP_TRAP_PORT) && dir != IP_CT_DIR_ORIGINAL)
1262 return NF_ACCEPT;
1263
1264 /* No NAT? */
1265 if (!(ct->status & IPS_NAT_MASK))
1266 return NF_ACCEPT;
1267
1268 /*
1269 * Make sure the packet length is ok. So far, we were only guaranteed
1270 * to have a valid length IP header plus 8 bytes, which means we have
1271 * enough room for a UDP header. Just verify the UDP length field so we
1272 * can mess around with the payload.
1273 */
1274 if (ntohs(udph->len) != (*pskb)->len - (iph->ihl << 2)) {
1275 if (net_ratelimit())
1276 printk(KERN_WARNING "SNMP: dropping malformed packet "
1277 "src=%u.%u.%u.%u dst=%u.%u.%u.%u\n",
1278 NIPQUAD(iph->saddr), NIPQUAD(iph->daddr));
1279 return NF_DROP;
1280 }
1281
1282 if (!skb_make_writable(pskb, (*pskb)->len))
1283 return NF_DROP;
1284
1285 spin_lock_bh(&snmp_lock);
1286 ret = snmp_translate(ct, ctinfo, pskb);
1287 spin_unlock_bh(&snmp_lock);
1288 return ret;
1289 }
1290
1291 static struct ip_conntrack_helper snmp_helper = {
1292 .max_expected = 0,
1293 .timeout = 180,
1294 .me = THIS_MODULE,
1295 .help = help,
1296 .name = "snmp",
1297
1298 .tuple = { .src = { .u = { __constant_htons(SNMP_PORT) } },
1299 .dst = { .protonum = IPPROTO_UDP },
1300 },
1301 .mask = { .src = { .u = { 0xFFFF } },
1302 .dst = { .protonum = 0xFF },
1303 },
1304 };
1305
1306 static struct ip_conntrack_helper snmp_trap_helper = {
1307 .max_expected = 0,
1308 .timeout = 180,
1309 .me = THIS_MODULE,
1310 .help = help,
1311 .name = "snmp_trap",
1312
1313 .tuple = { .src = { .u = { __constant_htons(SNMP_TRAP_PORT) } },
1314 .dst = { .protonum = IPPROTO_UDP },
1315 },
1316 .mask = { .src = { .u = { 0xFFFF } },
1317 .dst = { .protonum = 0xFF },
1318 },
1319 };
1320
1321 /*****************************************************************************
1322 *
1323 * Module stuff.
1324 *
1325 *****************************************************************************/
1326
1327 static int __init ip_nat_snmp_basic_init(void)
1328 {
1329 int ret = 0;
1330
1331 ret = ip_conntrack_helper_register(&snmp_helper);
1332 if (ret < 0)
1333 return ret;
1334 ret = ip_conntrack_helper_register(&snmp_trap_helper);
1335 if (ret < 0) {
1336 ip_conntrack_helper_unregister(&snmp_helper);
1337 return ret;
1338 }
1339 return ret;
1340 }
1341
1342 static void __exit ip_nat_snmp_basic_fini(void)
1343 {
1344 ip_conntrack_helper_unregister(&snmp_helper);
1345 ip_conntrack_helper_unregister(&snmp_trap_helper);
1346 }
1347
1348 module_init(ip_nat_snmp_basic_init);
1349 module_exit(ip_nat_snmp_basic_fini);
1350
1351 module_param(debug, bool, 0600);
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