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/module.h>
48 #include <linux/types.h>
49 #include <linux/kernel.h>
50 #include <linux/netfilter_ipv4.h>
51 #include <linux/netfilter_ipv4/ip_nat.h>
52 #include <linux/netfilter_ipv4/ip_nat_helper.h>
53 #include <linux/brlock.h>
54 #include <linux/types.h>
55 #include <linux/ip.h>
56 #include <net/checksum.h>
57 #include <net/udp.h>
58 #include <asm/uaccess.h>
59
60
61
62 #define SNMP_PORT 161
63 #define SNMP_TRAP_PORT 162
64 #define NOCT1(n) (u_int8_t )((n) & 0xff)
65
66 static int debug = 0;
67 static spinlock_t snmp_lock = SPIN_LOCK_UNLOCKED;
68
69 /*
70 * Application layer address mapping mimics the NAT mapping, but
71 * only for the first octet in this case (a more flexible system
72 * can be implemented if needed).
73 */
74 struct oct1_map
75 {
76 u_int8_t from;
77 u_int8_t to;
78 };
79
80
81 /*****************************************************************************
82 *
83 * Basic ASN.1 decoding routines (gxsnmp author Dirk Wisse)
84 *
85 *****************************************************************************/
86
87 /* Class */
88 #define ASN1_UNI 0 /* Universal */
89 #define ASN1_APL 1 /* Application */
90 #define ASN1_CTX 2 /* Context */
91 #define ASN1_PRV 3 /* Private */
92
93 /* Tag */
94 #define ASN1_EOC 0 /* End Of Contents */
95 #define ASN1_BOL 1 /* Boolean */
96 #define ASN1_INT 2 /* Integer */
97 #define ASN1_BTS 3 /* Bit String */
98 #define ASN1_OTS 4 /* Octet String */
99 #define ASN1_NUL 5 /* Null */
100 #define ASN1_OJI 6 /* Object Identifier */
101 #define ASN1_OJD 7 /* Object Description */
102 #define ASN1_EXT 8 /* External */
103 #define ASN1_SEQ 16 /* Sequence */
104 #define ASN1_SET 17 /* Set */
105 #define ASN1_NUMSTR 18 /* Numerical String */
106 #define ASN1_PRNSTR 19 /* Printable String */
107 #define ASN1_TEXSTR 20 /* Teletext String */
108 #define ASN1_VIDSTR 21 /* Video String */
109 #define ASN1_IA5STR 22 /* IA5 String */
110 #define ASN1_UNITIM 23 /* Universal Time */
111 #define ASN1_GENTIM 24 /* General Time */
112 #define ASN1_GRASTR 25 /* Graphical String */
113 #define ASN1_VISSTR 26 /* Visible String */
114 #define ASN1_GENSTR 27 /* General String */
115
116 /* Primitive / Constructed methods*/
117 #define ASN1_PRI 0 /* Primitive */
118 #define ASN1_CON 1 /* Constructed */
119
120 /*
121 * Error codes.
122 */
123 #define ASN1_ERR_NOERROR 0
124 #define ASN1_ERR_DEC_EMPTY 2
125 #define ASN1_ERR_DEC_EOC_MISMATCH 3
126 #define ASN1_ERR_DEC_LENGTH_MISMATCH 4
127 #define ASN1_ERR_DEC_BADVALUE 5
128
129 /*
130 * ASN.1 context.
131 */
132 struct asn1_ctx
133 {
134 int error; /* Error condition */
135 unsigned char *pointer; /* Octet just to be decoded */
136 unsigned char *begin; /* First octet */
137 unsigned char *end; /* Octet after last octet */
138 };
139
140 /*
141 * Octet string (not null terminated)
142 */
143 struct asn1_octstr
144 {
145 unsigned char *data;
146 unsigned int len;
147 };
148
asn1_open(struct asn1_ctx * ctx,unsigned char * buf,unsigned int len)149 static void asn1_open(struct asn1_ctx *ctx,
150 unsigned char *buf,
151 unsigned int len)
152 {
153 ctx->begin = buf;
154 ctx->end = buf + len;
155 ctx->pointer = buf;
156 ctx->error = ASN1_ERR_NOERROR;
157 }
158
asn1_octet_decode(struct asn1_ctx * ctx,unsigned char * ch)159 static unsigned char asn1_octet_decode(struct asn1_ctx *ctx, unsigned char *ch)
160 {
161 if (ctx->pointer >= ctx->end) {
162 ctx->error = ASN1_ERR_DEC_EMPTY;
163 return 0;
164 }
165 *ch = *(ctx->pointer)++;
166 return 1;
167 }
168
asn1_tag_decode(struct asn1_ctx * ctx,unsigned int * tag)169 static unsigned char asn1_tag_decode(struct asn1_ctx *ctx, unsigned int *tag)
170 {
171 unsigned char ch;
172
173 *tag = 0;
174
175 do
176 {
177 if (!asn1_octet_decode(ctx, &ch))
178 return 0;
179 *tag <<= 7;
180 *tag |= ch & 0x7F;
181 } while ((ch & 0x80) == 0x80);
182 return 1;
183 }
184
asn1_id_decode(struct asn1_ctx * ctx,unsigned int * cls,unsigned int * con,unsigned int * tag)185 static unsigned char asn1_id_decode(struct asn1_ctx *ctx,
186 unsigned int *cls,
187 unsigned int *con,
188 unsigned int *tag)
189 {
190 unsigned char ch;
191
192 if (!asn1_octet_decode(ctx, &ch))
193 return 0;
194
195 *cls = (ch & 0xC0) >> 6;
196 *con = (ch & 0x20) >> 5;
197 *tag = (ch & 0x1F);
198
199 if (*tag == 0x1F) {
200 if (!asn1_tag_decode(ctx, tag))
201 return 0;
202 }
203 return 1;
204 }
205
asn1_length_decode(struct asn1_ctx * ctx,unsigned int * def,unsigned int * len)206 static unsigned char asn1_length_decode(struct asn1_ctx *ctx,
207 unsigned int *def,
208 unsigned int *len)
209 {
210 unsigned char ch, cnt;
211
212 if (!asn1_octet_decode(ctx, &ch))
213 return 0;
214
215 if (ch == 0x80)
216 *def = 0;
217 else {
218 *def = 1;
219
220 if (ch < 0x80)
221 *len = ch;
222 else {
223 cnt = (unsigned char) (ch & 0x7F);
224 *len = 0;
225
226 while (cnt > 0) {
227 if (!asn1_octet_decode(ctx, &ch))
228 return 0;
229 *len <<= 8;
230 *len |= ch;
231 cnt--;
232 }
233 }
234 }
235
236 /* don't trust len bigger than ctx buffer */
237 if (*len > ctx->end - ctx->pointer)
238 return 0;
239
240 return 1;
241 }
242
asn1_header_decode(struct asn1_ctx * ctx,unsigned char ** eoc,unsigned int * cls,unsigned int * con,unsigned int * tag)243 static unsigned char asn1_header_decode(struct asn1_ctx *ctx,
244 unsigned char **eoc,
245 unsigned int *cls,
246 unsigned int *con,
247 unsigned int *tag)
248 {
249 unsigned int def, len;
250
251 if (!asn1_id_decode(ctx, cls, con, tag))
252 return 0;
253
254 if (!asn1_length_decode(ctx, &def, &len))
255 return 0;
256
257 /* primitive shall be definite, indefinite shall be constructed */
258 if (*con == ASN1_PRI && !def)
259 return 0;
260
261 if (def)
262 *eoc = ctx->pointer + len;
263 else
264 *eoc = 0;
265 return 1;
266 }
267
asn1_eoc_decode(struct asn1_ctx * ctx,unsigned char * eoc)268 static unsigned char asn1_eoc_decode(struct asn1_ctx *ctx, unsigned char *eoc)
269 {
270 unsigned char ch;
271
272 if (eoc == 0) {
273 if (!asn1_octet_decode(ctx, &ch))
274 return 0;
275
276 if (ch != 0x00) {
277 ctx->error = ASN1_ERR_DEC_EOC_MISMATCH;
278 return 0;
279 }
280
281 if (!asn1_octet_decode(ctx, &ch))
282 return 0;
283
284 if (ch != 0x00) {
285 ctx->error = ASN1_ERR_DEC_EOC_MISMATCH;
286 return 0;
287 }
288 return 1;
289 } else {
290 if (ctx->pointer != eoc) {
291 ctx->error = ASN1_ERR_DEC_LENGTH_MISMATCH;
292 return 0;
293 }
294 return 1;
295 }
296 }
297
asn1_null_decode(struct asn1_ctx * ctx,unsigned char * eoc)298 static unsigned char asn1_null_decode(struct asn1_ctx *ctx, unsigned char *eoc)
299 {
300 ctx->pointer = eoc;
301 return 1;
302 }
303
asn1_long_decode(struct asn1_ctx * ctx,unsigned char * eoc,long * integer)304 static unsigned char asn1_long_decode(struct asn1_ctx *ctx,
305 unsigned char *eoc,
306 long *integer)
307 {
308 unsigned char ch;
309 unsigned int len;
310
311 if (!asn1_octet_decode(ctx, &ch))
312 return 0;
313
314 *integer = (signed char) ch;
315 len = 1;
316
317 while (ctx->pointer < eoc) {
318 if (++len > sizeof (long)) {
319 ctx->error = ASN1_ERR_DEC_BADVALUE;
320 return 0;
321 }
322
323 if (!asn1_octet_decode(ctx, &ch))
324 return 0;
325
326 *integer <<= 8;
327 *integer |= ch;
328 }
329 return 1;
330 }
331
asn1_uint_decode(struct asn1_ctx * ctx,unsigned char * eoc,unsigned int * integer)332 static unsigned char asn1_uint_decode(struct asn1_ctx *ctx,
333 unsigned char *eoc,
334 unsigned int *integer)
335 {
336 unsigned char ch;
337 unsigned int len;
338
339 if (!asn1_octet_decode(ctx, &ch))
340 return 0;
341
342 *integer = ch;
343 if (ch == 0) len = 0;
344 else len = 1;
345
346 while (ctx->pointer < eoc) {
347 if (++len > sizeof (unsigned int)) {
348 ctx->error = ASN1_ERR_DEC_BADVALUE;
349 return 0;
350 }
351
352 if (!asn1_octet_decode(ctx, &ch))
353 return 0;
354
355 *integer <<= 8;
356 *integer |= ch;
357 }
358 return 1;
359 }
360
asn1_ulong_decode(struct asn1_ctx * ctx,unsigned char * eoc,unsigned long * integer)361 static unsigned char asn1_ulong_decode(struct asn1_ctx *ctx,
362 unsigned char *eoc,
363 unsigned long *integer)
364 {
365 unsigned char ch;
366 unsigned int len;
367
368 if (!asn1_octet_decode(ctx, &ch))
369 return 0;
370
371 *integer = ch;
372 if (ch == 0) len = 0;
373 else len = 1;
374
375 while (ctx->pointer < eoc) {
376 if (++len > sizeof (unsigned long)) {
377 ctx->error = ASN1_ERR_DEC_BADVALUE;
378 return 0;
379 }
380
381 if (!asn1_octet_decode(ctx, &ch))
382 return 0;
383
384 *integer <<= 8;
385 *integer |= ch;
386 }
387 return 1;
388 }
389
asn1_octets_decode(struct asn1_ctx * ctx,unsigned char * eoc,unsigned char ** octets,unsigned int * len)390 static unsigned char asn1_octets_decode(struct asn1_ctx *ctx,
391 unsigned char *eoc,
392 unsigned char **octets,
393 unsigned int *len)
394 {
395 unsigned char *ptr;
396
397 *len = 0;
398
399 *octets = kmalloc(eoc - ctx->pointer, GFP_ATOMIC);
400 if (*octets == NULL) {
401 if (net_ratelimit())
402 printk("OOM in bsalg (%d)\n", __LINE__);
403 return 0;
404 }
405
406 ptr = *octets;
407 while (ctx->pointer < eoc) {
408 if (!asn1_octet_decode(ctx, (unsigned char *)ptr++)) {
409 kfree(*octets);
410 *octets = NULL;
411 return 0;
412 }
413 (*len)++;
414 }
415 return 1;
416 }
417
asn1_subid_decode(struct asn1_ctx * ctx,unsigned long * subid)418 static unsigned char asn1_subid_decode(struct asn1_ctx *ctx,
419 unsigned long *subid)
420 {
421 unsigned char ch;
422
423 *subid = 0;
424
425 do {
426 if (!asn1_octet_decode(ctx, &ch))
427 return 0;
428
429 *subid <<= 7;
430 *subid |= ch & 0x7F;
431 } while ((ch & 0x80) == 0x80);
432 return 1;
433 }
434
asn1_oid_decode(struct asn1_ctx * ctx,unsigned char * eoc,unsigned long ** oid,unsigned int * len)435 static unsigned char asn1_oid_decode(struct asn1_ctx *ctx,
436 unsigned char *eoc,
437 unsigned long **oid,
438 unsigned int *len)
439 {
440 unsigned long subid;
441 unsigned int size;
442 unsigned long *optr;
443
444 size = eoc - ctx->pointer + 1;
445
446 /* first subid actually encodes first two subids */
447 if (size < 2 || size > ULONG_MAX/sizeof(unsigned long))
448 return 0;
449
450 *oid = kmalloc(size * sizeof(unsigned long), GFP_ATOMIC);
451 if (*oid == NULL) {
452 if (net_ratelimit())
453 printk("OOM in bsalg (%d)\n", __LINE__);
454 return 0;
455 }
456
457 optr = *oid;
458
459 if (!asn1_subid_decode(ctx, &subid)) {
460 kfree(*oid);
461 *oid = NULL;
462 return 0;
463 }
464
465 if (subid < 40) {
466 optr [0] = 0;
467 optr [1] = subid;
468 } else if (subid < 80) {
469 optr [0] = 1;
470 optr [1] = subid - 40;
471 } else {
472 optr [0] = 2;
473 optr [1] = subid - 80;
474 }
475
476 *len = 2;
477 optr += 2;
478
479 while (ctx->pointer < eoc) {
480 if (++(*len) > size) {
481 ctx->error = ASN1_ERR_DEC_BADVALUE;
482 kfree(*oid);
483 *oid = NULL;
484 return 0;
485 }
486
487 if (!asn1_subid_decode(ctx, optr++)) {
488 kfree(*oid);
489 *oid = NULL;
490 return 0;
491 }
492 }
493 return 1;
494 }
495
496 /*****************************************************************************
497 *
498 * SNMP decoding routines (gxsnmp author Dirk Wisse)
499 *
500 *****************************************************************************/
501
502 /* SNMP Versions */
503 #define SNMP_V1 0
504 #define SNMP_V2C 1
505 #define SNMP_V2 2
506 #define SNMP_V3 3
507
508 /* Default Sizes */
509 #define SNMP_SIZE_COMM 256
510 #define SNMP_SIZE_OBJECTID 128
511 #define SNMP_SIZE_BUFCHR 256
512 #define SNMP_SIZE_BUFINT 128
513 #define SNMP_SIZE_SMALLOBJECTID 16
514
515 /* Requests */
516 #define SNMP_PDU_GET 0
517 #define SNMP_PDU_NEXT 1
518 #define SNMP_PDU_RESPONSE 2
519 #define SNMP_PDU_SET 3
520 #define SNMP_PDU_TRAP1 4
521 #define SNMP_PDU_BULK 5
522 #define SNMP_PDU_INFORM 6
523 #define SNMP_PDU_TRAP2 7
524
525 /* Errors */
526 #define SNMP_NOERROR 0
527 #define SNMP_TOOBIG 1
528 #define SNMP_NOSUCHNAME 2
529 #define SNMP_BADVALUE 3
530 #define SNMP_READONLY 4
531 #define SNMP_GENERROR 5
532 #define SNMP_NOACCESS 6
533 #define SNMP_WRONGTYPE 7
534 #define SNMP_WRONGLENGTH 8
535 #define SNMP_WRONGENCODING 9
536 #define SNMP_WRONGVALUE 10
537 #define SNMP_NOCREATION 11
538 #define SNMP_INCONSISTENTVALUE 12
539 #define SNMP_RESOURCEUNAVAILABLE 13
540 #define SNMP_COMMITFAILED 14
541 #define SNMP_UNDOFAILED 15
542 #define SNMP_AUTHORIZATIONERROR 16
543 #define SNMP_NOTWRITABLE 17
544 #define SNMP_INCONSISTENTNAME 18
545
546 /* General SNMP V1 Traps */
547 #define SNMP_TRAP_COLDSTART 0
548 #define SNMP_TRAP_WARMSTART 1
549 #define SNMP_TRAP_LINKDOWN 2
550 #define SNMP_TRAP_LINKUP 3
551 #define SNMP_TRAP_AUTFAILURE 4
552 #define SNMP_TRAP_EQPNEIGHBORLOSS 5
553 #define SNMP_TRAP_ENTSPECIFIC 6
554
555 /* SNMPv1 Types */
556 #define SNMP_NULL 0
557 #define SNMP_INTEGER 1 /* l */
558 #define SNMP_OCTETSTR 2 /* c */
559 #define SNMP_DISPLAYSTR 2 /* c */
560 #define SNMP_OBJECTID 3 /* ul */
561 #define SNMP_IPADDR 4 /* uc */
562 #define SNMP_COUNTER 5 /* ul */
563 #define SNMP_GAUGE 6 /* ul */
564 #define SNMP_TIMETICKS 7 /* ul */
565 #define SNMP_OPAQUE 8 /* c */
566
567 /* Additional SNMPv2 Types */
568 #define SNMP_UINTEGER 5 /* ul */
569 #define SNMP_BITSTR 9 /* uc */
570 #define SNMP_NSAP 10 /* uc */
571 #define SNMP_COUNTER64 11 /* ul */
572 #define SNMP_NOSUCHOBJECT 12
573 #define SNMP_NOSUCHINSTANCE 13
574 #define SNMP_ENDOFMIBVIEW 14
575
576 union snmp_syntax
577 {
578 unsigned char uc[0]; /* 8 bit unsigned */
579 char c[0]; /* 8 bit signed */
580 unsigned long ul[0]; /* 32 bit unsigned */
581 long l[0]; /* 32 bit signed */
582 };
583
584 struct snmp_object
585 {
586 unsigned long *id;
587 unsigned int id_len;
588 unsigned short type;
589 unsigned int syntax_len;
590 union snmp_syntax syntax;
591 };
592
593 struct snmp_request
594 {
595 unsigned long id;
596 unsigned int error_status;
597 unsigned int error_index;
598 };
599
600 struct snmp_v1_trap
601 {
602 unsigned long *id;
603 unsigned int id_len;
604 unsigned long ip_address; /* pointer */
605 unsigned int general;
606 unsigned int specific;
607 unsigned long time;
608 };
609
610 /* SNMP types */
611 #define SNMP_IPA 0
612 #define SNMP_CNT 1
613 #define SNMP_GGE 2
614 #define SNMP_TIT 3
615 #define SNMP_OPQ 4
616 #define SNMP_C64 6
617
618 /* SNMP errors */
619 #define SERR_NSO 0
620 #define SERR_NSI 1
621 #define SERR_EOM 2
622
623 static void inline mangle_address(unsigned char *begin,
624 unsigned char *addr,
625 const struct oct1_map *map,
626 u_int16_t *check);
627 struct snmp_cnv
628 {
629 unsigned int class;
630 unsigned int tag;
631 int syntax;
632 };
633
634 static struct snmp_cnv snmp_conv [] =
635 {
636 {ASN1_UNI, ASN1_NUL, SNMP_NULL},
637 {ASN1_UNI, ASN1_INT, SNMP_INTEGER},
638 {ASN1_UNI, ASN1_OTS, SNMP_OCTETSTR},
639 {ASN1_UNI, ASN1_OTS, SNMP_DISPLAYSTR},
640 {ASN1_UNI, ASN1_OJI, SNMP_OBJECTID},
641 {ASN1_APL, SNMP_IPA, SNMP_IPADDR},
642 {ASN1_APL, SNMP_CNT, SNMP_COUNTER}, /* Counter32 */
643 {ASN1_APL, SNMP_GGE, SNMP_GAUGE}, /* Gauge32 == Unsigned32 */
644 {ASN1_APL, SNMP_TIT, SNMP_TIMETICKS},
645 {ASN1_APL, SNMP_OPQ, SNMP_OPAQUE},
646
647 /* SNMPv2 data types and errors */
648 {ASN1_UNI, ASN1_BTS, SNMP_BITSTR},
649 {ASN1_APL, SNMP_C64, SNMP_COUNTER64},
650 {ASN1_CTX, SERR_NSO, SNMP_NOSUCHOBJECT},
651 {ASN1_CTX, SERR_NSI, SNMP_NOSUCHINSTANCE},
652 {ASN1_CTX, SERR_EOM, SNMP_ENDOFMIBVIEW},
653 {0, 0, -1}
654 };
655
snmp_tag_cls2syntax(unsigned int tag,unsigned int cls,unsigned short * syntax)656 static unsigned char snmp_tag_cls2syntax(unsigned int tag,
657 unsigned int cls,
658 unsigned short *syntax)
659 {
660 struct snmp_cnv *cnv;
661
662 cnv = snmp_conv;
663
664 while (cnv->syntax != -1) {
665 if (cnv->tag == tag && cnv->class == cls) {
666 *syntax = cnv->syntax;
667 return 1;
668 }
669 cnv++;
670 }
671 return 0;
672 }
673
snmp_object_decode(struct asn1_ctx * ctx,struct snmp_object ** obj)674 static unsigned char snmp_object_decode(struct asn1_ctx *ctx,
675 struct snmp_object **obj)
676 {
677 unsigned int cls, con, tag, len, idlen;
678 unsigned short type;
679 unsigned char *eoc, *end, *p;
680 unsigned long *lp, *id;
681 unsigned long ul;
682 long l;
683
684 *obj = NULL;
685 id = NULL;
686
687 if (!asn1_header_decode(ctx, &eoc, &cls, &con, &tag))
688 return 0;
689
690 if (cls != ASN1_UNI || con != ASN1_CON || tag != ASN1_SEQ)
691 return 0;
692
693 if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
694 return 0;
695
696 if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_OJI)
697 return 0;
698
699 if (!asn1_oid_decode(ctx, end, &id, &idlen))
700 return 0;
701
702 if (!asn1_header_decode(ctx, &end, &cls, &con, &tag)) {
703 kfree(id);
704 return 0;
705 }
706
707 if (con != ASN1_PRI) {
708 kfree(id);
709 return 0;
710 }
711
712 if (!snmp_tag_cls2syntax(tag, cls, &type)) {
713 kfree(id);
714 return 0;
715 }
716
717 switch (type) {
718 case SNMP_INTEGER:
719 len = sizeof(long);
720 if (!asn1_long_decode(ctx, end, &l)) {
721 kfree(id);
722 return 0;
723 }
724 *obj = kmalloc(sizeof(struct snmp_object) + len,
725 GFP_ATOMIC);
726 if (*obj == NULL) {
727 kfree(id);
728 if (net_ratelimit())
729 printk("OOM in bsalg (%d)\n", __LINE__);
730 return 0;
731 }
732 (*obj)->syntax.l[0] = l;
733 break;
734 case SNMP_OCTETSTR:
735 case SNMP_OPAQUE:
736 if (!asn1_octets_decode(ctx, end, &p, &len)) {
737 kfree(id);
738 return 0;
739 }
740 *obj = kmalloc(sizeof(struct snmp_object) + len,
741 GFP_ATOMIC);
742 if (*obj == NULL) {
743 kfree(p);
744 kfree(id);
745 if (net_ratelimit())
746 printk("OOM in bsalg (%d)\n", __LINE__);
747 return 0;
748 }
749 memcpy((*obj)->syntax.c, p, len);
750 kfree(p);
751 break;
752 case SNMP_NULL:
753 case SNMP_NOSUCHOBJECT:
754 case SNMP_NOSUCHINSTANCE:
755 case SNMP_ENDOFMIBVIEW:
756 len = 0;
757 *obj = kmalloc(sizeof(struct snmp_object), GFP_ATOMIC);
758 if (*obj == NULL) {
759 kfree(id);
760 if (net_ratelimit())
761 printk("OOM in bsalg (%d)\n", __LINE__);
762 return 0;
763 }
764 if (!asn1_null_decode(ctx, end)) {
765 kfree(id);
766 kfree(*obj);
767 *obj = NULL;
768 return 0;
769 }
770 break;
771 case SNMP_OBJECTID:
772 if (!asn1_oid_decode(ctx, end, (unsigned long **)&lp, &len)) {
773 kfree(id);
774 return 0;
775 }
776 len *= sizeof(unsigned long);
777 *obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
778 if (*obj == NULL) {
779 kfree(id);
780 if (net_ratelimit())
781 printk("OOM in bsalg (%d)\n", __LINE__);
782 return 0;
783 }
784 memcpy((*obj)->syntax.ul, lp, len);
785 kfree(lp);
786 break;
787 case SNMP_IPADDR:
788 if (!asn1_octets_decode(ctx, end, &p, &len)) {
789 kfree(id);
790 return 0;
791 }
792 if (len != 4) {
793 kfree(p);
794 kfree(id);
795 return 0;
796 }
797 *obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
798 if (*obj == NULL) {
799 kfree(p);
800 kfree(id);
801 if (net_ratelimit())
802 printk("OOM in bsalg (%d)\n", __LINE__);
803 return 0;
804 }
805 memcpy((*obj)->syntax.uc, p, len);
806 kfree(p);
807 break;
808 case SNMP_COUNTER:
809 case SNMP_GAUGE:
810 case SNMP_TIMETICKS:
811 len = sizeof(unsigned long);
812 if (!asn1_ulong_decode(ctx, end, &ul)) {
813 kfree(id);
814 return 0;
815 }
816 *obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
817 if (*obj == NULL) {
818 kfree(id);
819 if (net_ratelimit())
820 printk("OOM in bsalg (%d)\n", __LINE__);
821 return 0;
822 }
823 (*obj)->syntax.ul[0] = ul;
824 break;
825 default:
826 kfree(id);
827 return 0;
828 }
829
830 (*obj)->syntax_len = len;
831 (*obj)->type = type;
832 (*obj)->id = id;
833 (*obj)->id_len = idlen;
834
835 if (!asn1_eoc_decode(ctx, eoc)) {
836 kfree(id);
837 kfree(*obj);
838 *obj = NULL;
839 return 0;
840 }
841 return 1;
842 }
843
snmp_request_decode(struct asn1_ctx * ctx,struct snmp_request * request)844 static unsigned char snmp_request_decode(struct asn1_ctx *ctx,
845 struct snmp_request *request)
846 {
847 unsigned int cls, con, tag;
848 unsigned char *end;
849
850 if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
851 return 0;
852
853 if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
854 return 0;
855
856 if (!asn1_ulong_decode(ctx, end, &request->id))
857 return 0;
858
859 if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
860 return 0;
861
862 if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
863 return 0;
864
865 if (!asn1_uint_decode(ctx, end, &request->error_status))
866 return 0;
867
868 if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
869 return 0;
870
871 if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
872 return 0;
873
874 if (!asn1_uint_decode(ctx, end, &request->error_index))
875 return 0;
876
877 return 1;
878 }
879
880 /*
881 * Fast checksum update for possibly oddly-aligned UDP byte, from the
882 * code example in the draft.
883 */
fast_csum(unsigned char * csum,const unsigned char * optr,const unsigned char * nptr,int odd)884 static void fast_csum(unsigned char *csum,
885 const unsigned char *optr,
886 const unsigned char *nptr,
887 int odd)
888 {
889 long x, old, new;
890
891 x = csum[0] * 256 + csum[1];
892
893 x =~ x & 0xFFFF;
894
895 if (odd) old = optr[0] * 256;
896 else old = optr[0];
897
898 x -= old & 0xFFFF;
899 if (x <= 0) {
900 x--;
901 x &= 0xFFFF;
902 }
903
904 if (odd) new = nptr[0] * 256;
905 else new = nptr[0];
906
907 x += new & 0xFFFF;
908 if (x & 0x10000) {
909 x++;
910 x &= 0xFFFF;
911 }
912
913 x =~ x & 0xFFFF;
914 csum[0] = x / 256;
915 csum[1] = x & 0xFF;
916 }
917
918 /*
919 * Mangle IP address.
920 * - begin points to the start of the snmp messgae
921 * - addr points to the start of the address
922 */
mangle_address(unsigned char * begin,unsigned char * addr,const struct oct1_map * map,u_int16_t * check)923 static void inline mangle_address(unsigned char *begin,
924 unsigned char *addr,
925 const struct oct1_map *map,
926 u_int16_t *check)
927 {
928 if (map->from == NOCT1(*addr)) {
929 u_int32_t old;
930
931 if (debug)
932 memcpy(&old, (unsigned char *)addr, sizeof(old));
933
934 *addr = map->to;
935
936 /* Update UDP checksum if being used */
937 if (*check) {
938 unsigned char odd = !((addr - begin) % 2);
939
940 fast_csum((unsigned char *)check,
941 &map->from, &map->to, odd);
942
943 }
944
945 if (debug)
946 printk(KERN_DEBUG "bsalg: mapped %u.%u.%u.%u to "
947 "%u.%u.%u.%u\n", NIPQUAD(old), NIPQUAD(*addr));
948 }
949 }
950
snmp_trap_decode(struct asn1_ctx * ctx,struct snmp_v1_trap * trap,const struct oct1_map * map,u_int16_t * check)951 static unsigned char snmp_trap_decode(struct asn1_ctx *ctx,
952 struct snmp_v1_trap *trap,
953 const struct oct1_map *map,
954 u_int16_t *check)
955 {
956 unsigned int cls, con, tag, len;
957 unsigned char *end;
958
959 if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
960 return 0;
961
962 if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_OJI)
963 return 0;
964
965 if (!asn1_oid_decode(ctx, end, &trap->id, &trap->id_len))
966 return 0;
967
968 if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
969 goto err_id_free;
970
971 if (!((cls == ASN1_APL && con == ASN1_PRI && tag == SNMP_IPA) ||
972 (cls == ASN1_UNI && con == ASN1_PRI && tag == ASN1_OTS)))
973 goto err_id_free;
974
975 if (!asn1_octets_decode(ctx, end, (unsigned char **)&trap->ip_address, &len))
976 goto err_id_free;
977
978 /* IPv4 only */
979 if (len != 4)
980 goto err_addr_free;
981
982 mangle_address(ctx->begin, ctx->pointer - 4, map, check);
983
984 if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
985 goto err_addr_free;
986
987 if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
988 goto err_addr_free;;
989
990 if (!asn1_uint_decode(ctx, end, &trap->general))
991 goto err_addr_free;;
992
993 if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
994 goto err_addr_free;
995
996 if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
997 goto err_addr_free;
998
999 if (!asn1_uint_decode(ctx, end, &trap->specific))
1000 goto err_addr_free;
1001
1002 if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
1003 goto err_addr_free;
1004
1005 if (!((cls == ASN1_APL && con == ASN1_PRI && tag == SNMP_TIT) ||
1006 (cls == ASN1_UNI && con == ASN1_PRI && tag == ASN1_INT)))
1007 goto err_addr_free;
1008
1009 if (!asn1_ulong_decode(ctx, end, &trap->time))
1010 goto err_addr_free;
1011
1012 return 1;
1013
1014 err_addr_free:
1015 kfree((unsigned long *)trap->ip_address);
1016
1017 err_id_free:
1018 kfree(trap->id);
1019
1020 return 0;
1021 }
1022
1023 /*****************************************************************************
1024 *
1025 * Misc. routines
1026 *
1027 *****************************************************************************/
1028
hex_dump(unsigned char * buf,size_t len)1029 static void hex_dump(unsigned char *buf, size_t len)
1030 {
1031 size_t i;
1032
1033 for (i = 0; i < len; i++) {
1034 if (i && !(i % 16))
1035 printk("\n");
1036 printk("%02x ", *(buf + i));
1037 }
1038 printk("\n");
1039 }
1040
1041 /*
1042 * Parse and mangle SNMP message according to mapping.
1043 * (And this is the fucking 'basic' method).
1044 */
snmp_parse_mangle(unsigned char * msg,u_int16_t len,const struct oct1_map * map,u_int16_t * check)1045 static int snmp_parse_mangle(unsigned char *msg,
1046 u_int16_t len,
1047 const struct oct1_map *map,
1048 u_int16_t *check)
1049 {
1050 unsigned char *eoc, *end;
1051 unsigned int cls, con, tag, vers, pdutype;
1052 struct asn1_ctx ctx;
1053 struct asn1_octstr comm;
1054 struct snmp_object **obj;
1055
1056 if (debug > 1)
1057 hex_dump(msg, len);
1058
1059 asn1_open(&ctx, msg, len);
1060
1061 /*
1062 * Start of SNMP message.
1063 */
1064 if (!asn1_header_decode(&ctx, &eoc, &cls, &con, &tag))
1065 return 0;
1066 if (cls != ASN1_UNI || con != ASN1_CON || tag != ASN1_SEQ)
1067 return 0;
1068
1069 /*
1070 * Version 1 or 2 handled.
1071 */
1072 if (!asn1_header_decode(&ctx, &end, &cls, &con, &tag))
1073 return 0;
1074 if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
1075 return 0;
1076 if (!asn1_uint_decode (&ctx, end, &vers))
1077 return 0;
1078 if (debug > 1)
1079 printk(KERN_DEBUG "bsalg: snmp version: %u\n", vers + 1);
1080 if (vers > 1)
1081 return 1;
1082
1083 /*
1084 * Community.
1085 */
1086 if (!asn1_header_decode (&ctx, &end, &cls, &con, &tag))
1087 return 0;
1088 if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_OTS)
1089 return 0;
1090 if (!asn1_octets_decode(&ctx, end, &comm.data, &comm.len))
1091 return 0;
1092 if (debug > 1) {
1093 unsigned int i;
1094
1095 printk(KERN_DEBUG "bsalg: community: ");
1096 for (i = 0; i < comm.len; i++)
1097 printk("%c", comm.data[i]);
1098 printk("\n");
1099 }
1100 kfree(comm.data);
1101
1102 /*
1103 * PDU type
1104 */
1105 if (!asn1_header_decode(&ctx, &eoc, &cls, &con, &pdutype))
1106 return 0;
1107 if (cls != ASN1_CTX || con != ASN1_CON)
1108 return 0;
1109 if (debug > 1) {
1110 unsigned char *pdus[] = {
1111 [SNMP_PDU_GET] = "get",
1112 [SNMP_PDU_NEXT] = "get-next",
1113 [SNMP_PDU_RESPONSE] = "response",
1114 [SNMP_PDU_SET] = "set",
1115 [SNMP_PDU_TRAP1] = "trapv1",
1116 [SNMP_PDU_BULK] = "bulk",
1117 [SNMP_PDU_INFORM] = "inform",
1118 [SNMP_PDU_TRAP2] = "trapv2"
1119 };
1120
1121 if (pdutype > SNMP_PDU_TRAP2)
1122 printk(KERN_DEBUG "bsalg: bad pdu type %u\n", pdutype);
1123 else
1124 printk(KERN_DEBUG "bsalg: pdu: %s\n", pdus[pdutype]);
1125 }
1126 if (pdutype != SNMP_PDU_RESPONSE &&
1127 pdutype != SNMP_PDU_TRAP1 && pdutype != SNMP_PDU_TRAP2)
1128 return 1;
1129
1130 /*
1131 * Request header or v1 trap
1132 */
1133 if (pdutype == SNMP_PDU_TRAP1) {
1134 struct snmp_v1_trap trap;
1135 unsigned char ret = snmp_trap_decode(&ctx, &trap, map, check);
1136
1137 if (ret) {
1138 kfree(trap.id);
1139 kfree((unsigned long *)trap.ip_address);
1140 } else
1141 return ret;
1142
1143 } else {
1144 struct snmp_request req;
1145
1146 if (!snmp_request_decode(&ctx, &req))
1147 return 0;
1148
1149 if (debug > 1)
1150 printk(KERN_DEBUG "bsalg: request: id=0x%lx error_status=%u "
1151 "error_index=%u\n", req.id, req.error_status,
1152 req.error_index);
1153 }
1154
1155 /*
1156 * Loop through objects, look for IP addresses to mangle.
1157 */
1158 if (!asn1_header_decode(&ctx, &eoc, &cls, &con, &tag))
1159 return 0;
1160
1161 if (cls != ASN1_UNI || con != ASN1_CON || tag != ASN1_SEQ)
1162 return 0;
1163
1164 obj = kmalloc(sizeof(struct snmp_object), GFP_ATOMIC);
1165 if (obj == NULL) {
1166 if (net_ratelimit())
1167 printk(KERN_WARNING "OOM in bsalg(%d)\n", __LINE__);
1168 return 0;
1169 }
1170
1171 while (!asn1_eoc_decode(&ctx, eoc)) {
1172 unsigned int i;
1173
1174 if (!snmp_object_decode(&ctx, obj)) {
1175 if (*obj) {
1176 if ((*obj)->id)
1177 kfree((*obj)->id);
1178 kfree(*obj);
1179 }
1180 kfree(obj);
1181 return 0;
1182 }
1183
1184 if (debug > 1) {
1185 printk(KERN_DEBUG "bsalg: object: ");
1186 for (i = 0; i < (*obj)->id_len; i++) {
1187 if (i > 0)
1188 printk(".");
1189 printk("%lu", (*obj)->id[i]);
1190 }
1191 printk(": type=%u\n", (*obj)->type);
1192
1193 }
1194
1195 if ((*obj)->type == SNMP_IPADDR)
1196 mangle_address(ctx.begin, ctx.pointer - 4 , map, check);
1197
1198 kfree((*obj)->id);
1199 kfree(*obj);
1200 }
1201 kfree(obj);
1202
1203 if (!asn1_eoc_decode(&ctx, eoc))
1204 return 0;
1205
1206 return 1;
1207 }
1208
1209 /*****************************************************************************
1210 *
1211 * NAT routines.
1212 *
1213 *****************************************************************************/
1214
1215 /*
1216 * SNMP translation routine.
1217 */
snmp_translate(struct ip_conntrack * ct,struct ip_nat_info * info,enum ip_conntrack_info ctinfo,unsigned int hooknum,struct sk_buff ** pskb)1218 static int snmp_translate(struct ip_conntrack *ct,
1219 struct ip_nat_info *info,
1220 enum ip_conntrack_info ctinfo,
1221 unsigned int hooknum,
1222 struct sk_buff **pskb)
1223 {
1224 struct iphdr *iph = (*pskb)->nh.iph;
1225 struct udphdr *udph = (struct udphdr *)((u_int32_t *)iph + iph->ihl);
1226 u_int16_t udplen = ntohs(udph->len);
1227 u_int16_t paylen = udplen - sizeof(struct udphdr);
1228 int dir = CTINFO2DIR(ctinfo);
1229 struct oct1_map map;
1230
1231 /*
1232 * Determine mappping for application layer addresses based
1233 * on NAT manipulations for the packet.
1234 */
1235 if (dir == IP_CT_DIR_ORIGINAL) {
1236 /* SNAT traps */
1237 map.from = NOCT1(ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.ip);
1238 map.to = NOCT1(ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.ip);
1239 } else {
1240 /* DNAT replies */
1241 map.from = NOCT1(ct->tuplehash[IP_CT_DIR_REPLY].tuple.src.ip);
1242 map.to = NOCT1(ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.dst.ip);
1243 }
1244
1245 if (map.from == map.to)
1246 return NF_ACCEPT;
1247
1248 if (!snmp_parse_mangle((unsigned char *)udph + sizeof(struct udphdr),
1249 paylen, &map, &udph->check)) {
1250 printk(KERN_WARNING "bsalg: parser failed\n");
1251 return NF_DROP;
1252 }
1253 return NF_ACCEPT;
1254 }
1255
1256 /*
1257 * NAT helper function, packets arrive here from NAT code.
1258 */
nat_help(struct ip_conntrack * ct,struct ip_conntrack_expect * exp,struct ip_nat_info * info,enum ip_conntrack_info ctinfo,unsigned int hooknum,struct sk_buff ** pskb)1259 static unsigned int nat_help(struct ip_conntrack *ct,
1260 struct ip_conntrack_expect *exp,
1261 struct ip_nat_info *info,
1262 enum ip_conntrack_info ctinfo,
1263 unsigned int hooknum,
1264 struct sk_buff **pskb)
1265 {
1266 int dir = CTINFO2DIR(ctinfo);
1267 struct iphdr *iph = (*pskb)->nh.iph;
1268 struct udphdr *udph = (struct udphdr *)((u_int32_t *)iph + iph->ihl);
1269
1270 spin_lock_bh(&snmp_lock);
1271
1272 /*
1273 * Translate snmp replies on pre-routing (DNAT) and snmp traps
1274 * on post routing (SNAT).
1275 */
1276 if (!((dir == IP_CT_DIR_REPLY && hooknum == NF_IP_PRE_ROUTING &&
1277 udph->source == ntohs(SNMP_PORT)) ||
1278 (dir == IP_CT_DIR_ORIGINAL && hooknum == NF_IP_POST_ROUTING &&
1279 udph->dest == ntohs(SNMP_TRAP_PORT)))) {
1280 spin_unlock_bh(&snmp_lock);
1281 return NF_ACCEPT;
1282 }
1283
1284 if (debug > 1) {
1285 printk(KERN_DEBUG "bsalg: dir=%s hook=%d manip=%s len=%d "
1286 "src=%u.%u.%u.%u:%u dst=%u.%u.%u.%u:%u "
1287 "osrc=%u.%u.%u.%u odst=%u.%u.%u.%u "
1288 "rsrc=%u.%u.%u.%u rdst=%u.%u.%u.%u "
1289 "\n",
1290 dir == IP_CT_DIR_REPLY ? "reply" : "orig", hooknum,
1291 HOOK2MANIP(hooknum) == IP_NAT_MANIP_SRC ? "snat" :
1292 "dnat", (*pskb)->len,
1293 NIPQUAD(iph->saddr), ntohs(udph->source),
1294 NIPQUAD(iph->daddr), ntohs(udph->dest),
1295 NIPQUAD(ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.ip),
1296 NIPQUAD(ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.dst.ip),
1297 NIPQUAD(ct->tuplehash[IP_CT_DIR_REPLY].tuple.src.ip),
1298 NIPQUAD(ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.ip));
1299 }
1300
1301 /*
1302 * Make sure the packet length is ok. So far, we were only guaranteed
1303 * to have a valid length IP header plus 8 bytes, which means we have
1304 * enough room for a UDP header. Just verify the UDP length field so we
1305 * can mess around with the payload.
1306 */
1307 if (ntohs(udph->len) == (*pskb)->len - (iph->ihl << 2)) {
1308 int ret = snmp_translate(ct, info, ctinfo, hooknum, pskb);
1309 spin_unlock_bh(&snmp_lock);
1310 return ret;
1311 }
1312
1313 if (net_ratelimit())
1314 printk(KERN_WARNING "bsalg: dropping malformed packet "
1315 "src=%u.%u.%u.%u dst=%u.%u.%u.%u\n",
1316 NIPQUAD(iph->saddr), NIPQUAD(iph->daddr));
1317 spin_unlock_bh(&snmp_lock);
1318 return NF_DROP;
1319 }
1320
1321 static struct ip_nat_helper snmp = {
1322 { NULL, NULL },
1323 "snmp",
1324 IP_NAT_HELPER_F_STANDALONE,
1325 THIS_MODULE,
1326 { { 0, { .udp = { __constant_htons(SNMP_PORT) } } },
1327 { 0, { 0 }, IPPROTO_UDP } },
1328 { { 0, { .udp = { 0xFFFF } } },
1329 { 0, { 0 }, 0xFFFF } },
1330 nat_help, NULL };
1331
1332 static struct ip_nat_helper snmp_trap = {
1333 { NULL, NULL },
1334 "snmp_trap",
1335 IP_NAT_HELPER_F_STANDALONE,
1336 THIS_MODULE,
1337 { { 0, { .udp = { __constant_htons(SNMP_TRAP_PORT) } } },
1338 { 0, { 0 }, IPPROTO_UDP } },
1339 { { 0, { .udp = { 0xFFFF } } },
1340 { 0, { 0 }, 0xFFFF } },
1341 nat_help, NULL };
1342
1343 /*****************************************************************************
1344 *
1345 * Module stuff.
1346 *
1347 *****************************************************************************/
1348
init(void)1349 static int __init init(void)
1350 {
1351 int ret = 0;
1352
1353 ret = ip_nat_helper_register(&snmp);
1354 if (ret < 0)
1355 return ret;
1356 ret = ip_nat_helper_register(&snmp_trap);
1357 if (ret < 0) {
1358 ip_nat_helper_unregister(&snmp);
1359 return ret;
1360 }
1361 return ret;
1362 }
1363
fini(void)1364 static void __exit fini(void)
1365 {
1366 ip_nat_helper_unregister(&snmp);
1367 ip_nat_helper_unregister(&snmp_trap);
1368 br_write_lock_bh(BR_NETPROTO_LOCK);
1369 br_write_unlock_bh(BR_NETPROTO_LOCK);
1370 }
1371
1372 module_init(init);
1373 module_exit(fini);
1374
1375 MODULE_PARM(debug, "i");
1376 MODULE_DESCRIPTION("Basic SNMP Application Layer Gateway");
1377 MODULE_LICENSE("GPL");
1378