net/ipv4/netfilter/ip_nat_snmp_basic.c

   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/in.h>
  47 #include <linux/module.h>
  48 #include <linux/types.h>
  49 #include <linux/kernel.h>
  50 #include <linux/moduleparam.h>
  51 #include <linux/netfilter_ipv4.h>
  52 #include <linux/netfilter_ipv4/ip_nat.h>
  53 #include <linux/netfilter_ipv4/ip_conntrack_helper.h>
  54 #include <linux/netfilter_ipv4/ip_nat_helper.h>
  55 #include <linux/ip.h>
  56 #include <linux/udp.h>
  57 #include <net/checksum.h>
  58 #include <net/udp.h>
  59 #include <asm/uaccess.h>
  60
  61 MODULE_LICENSE("GPL");
  62 MODULE_AUTHOR("James Morris <jmorris@intercode.com.au>");
  63 MODULE_DESCRIPTION("Basic SNMP Application Layer Gateway");
  64
  65 #define SNMP_PORT 161
  66 #define SNMP_TRAP_PORT 162
  67 #define NOCT1(n) (*(u8 *)n)
  68
  69 static int debug;
  70 static DEFINE_SPINLOCK(snmp_lock);
  71
  72 /*
  73  * Application layer address mapping mimics the NAT mapping, but
  74  * only for the first octet in this case (a more flexible system
  75  * can be implemented if needed).
  76  */
  77 struct oct1_map
  78 {
  79         u_int8_t from;
  80         u_int8_t to;
  81 };
  82
  83
  84 /*****************************************************************************
  85  *
  86  * Basic ASN.1 decoding routines (gxsnmp author Dirk Wisse)
  87  *
  88  *****************************************************************************/
  89
  90 /* Class */
  91 #define ASN1_UNI        0       /* Universal */
  92 #define ASN1_APL        1       /* Application */
  93 #define ASN1_CTX        2       /* Context */
  94 #define ASN1_PRV        3       /* Private */
  95
  96 /* Tag */
  97 #define ASN1_EOC        0       /* End Of Contents */
  98 #define ASN1_BOL        1       /* Boolean */
  99 #define ASN1_INT        2       /* Integer */
 100 #define ASN1_BTS        3       /* Bit String */
 101 #define ASN1_OTS        4       /* Octet String */
 102 #define ASN1_NUL        5       /* Null */
 103 #define ASN1_OJI        6       /* Object Identifier  */
 104 #define ASN1_OJD        7       /* Object Description */
 105 #define ASN1_EXT        8       /* External */
 106 #define ASN1_SEQ        16      /* Sequence */
 107 #define ASN1_SET        17      /* Set */
 108 #define ASN1_NUMSTR     18      /* Numerical String */
 109 #define ASN1_PRNSTR     19      /* Printable String */
 110 #define ASN1_TEXSTR     20      /* Teletext String */
 111 #define ASN1_VIDSTR     21      /* Video String */
 112 #define ASN1_IA5STR     22      /* IA5 String */
 113 #define ASN1_UNITIM     23      /* Universal Time */
 114 #define ASN1_GENTIM     24      /* General Time */
 115 #define ASN1_GRASTR     25      /* Graphical String */
 116 #define ASN1_VISSTR     26      /* Visible String */
 117 #define ASN1_GENSTR     27      /* General String */
 118
 119 /* Primitive / Constructed methods*/
 120 #define ASN1_PRI        0       /* Primitive */
 121 #define ASN1_CON        1       /* Constructed */
 122
 123 /*
 124  * Error codes.
 125  */
 126 #define ASN1_ERR_NOERROR                0
 127 #define ASN1_ERR_DEC_EMPTY              2
 128 #define ASN1_ERR_DEC_EOC_MISMATCH       3
 129 #define ASN1_ERR_DEC_LENGTH_MISMATCH    4
 130 #define ASN1_ERR_DEC_BADVALUE           5
 131
 132 /*
 133  * ASN.1 context.
 134  */
 135 struct asn1_ctx
 136 {
 137         int error;                      /* Error condition */
 138         unsigned char *pointer;         /* Octet just to be decoded */
 139         unsigned char *begin;           /* First octet */
 140         unsigned char *end;             /* Octet after last octet */
 141 };
 142
 143 /*
 144  * Octet string (not null terminated)
 145  */
 146 struct asn1_octstr
 147 {
 148         unsigned char *data;
 149         unsigned int len;
 150 };
 151
 152 static void asn1_open(struct asn1_ctx *ctx,
 153                       unsigned char *buf,
 154                       unsigned int len)
 155 {
 156         ctx->begin = buf;
 157         ctx->end = buf + len;
 158         ctx->pointer = buf;
 159         ctx->error = ASN1_ERR_NOERROR;
 160 }
 161
 162 static unsigned char asn1_octet_decode(struct asn1_ctx *ctx, unsigned char *ch)
 163 {
 164         if (ctx->pointer >= ctx->end) {
 165                 ctx->error = ASN1_ERR_DEC_EMPTY;
 166                 return 0;
 167         }
 168         *ch = *(ctx->pointer)++;
 169         return 1;
 170 }
 171
 172 static unsigned char asn1_tag_decode(struct asn1_ctx *ctx, unsigned int *tag)
 173 {
 174         unsigned char ch;
 175
 176         *tag = 0;
 177
 178         do
 179         {
 180                 if (!asn1_octet_decode(ctx, &ch))
 181                         return 0;
 182                 *tag <<= 7;
 183                 *tag |= ch & 0x7F;
 184         } while ((ch & 0x80) == 0x80);
 185         return 1;
 186 }
 187
 188 static unsigned char asn1_id_decode(struct asn1_ctx *ctx,
 189                                     unsigned int *cls,
 190                                     unsigned int *con,
 191                                     unsigned int *tag)
 192 {
 193         unsigned char ch;
 194
 195         if (!asn1_octet_decode(ctx, &ch))
 196                 return 0;
 197
 198         *cls = (ch & 0xC0) >> 6;
 199         *con = (ch & 0x20) >> 5;
 200         *tag = (ch & 0x1F);
 201
 202         if (*tag == 0x1F) {
 203                 if (!asn1_tag_decode(ctx, tag))
 204                         return 0;
 205         }
 206         return 1;
 207 }
 208
 209 static unsigned char asn1_length_decode(struct asn1_ctx *ctx,
 210                                         unsigned int *def,
 211                                         unsigned int *len)
 212 {
 213         unsigned char ch, cnt;
 214
 215         if (!asn1_octet_decode(ctx, &ch))
 216                 return 0;
 217
 218         if (ch == 0x80)
 219                 *def = 0;
 220         else {
 221                 *def = 1;
 222
 223                 if (ch < 0x80)
 224                         *len = ch;
 225                 else {
 226                         cnt = (unsigned char) (ch & 0x7F);
 227                         *len = 0;
 228
 229                         while (cnt > 0) {
 230                                 if (!asn1_octet_decode(ctx, &ch))
 231                                         return 0;
 232                                 *len <<= 8;
 233                                 *len |= ch;
 234                                 cnt--;
 235                         }
 236                 }
 237         }
 238         return 1;
 239 }
 240
 241 static unsigned char asn1_header_decode(struct asn1_ctx *ctx,
 242                                         unsigned char **eoc,
 243                                         unsigned int *cls,
 244                                         unsigned int *con,
 245                                         unsigned int *tag)
 246 {
 247         unsigned int def, len;
 248
 249         if (!asn1_id_decode(ctx, cls, con, tag))
 250                 return 0;
 251
 252         def = len = 0;
 253         if (!asn1_length_decode(ctx, &def, &len))
 254                 return 0;
 255
 256         if (def)
 257                 *eoc = ctx->pointer + len;
 258         else
 259                 *eoc = NULL;
 260         return 1;
 261 }
 262
 263 static unsigned char asn1_eoc_decode(struct asn1_ctx *ctx, unsigned char *eoc)
 264 {
 265         unsigned char ch;
 266
 267         if (eoc == 0) {
 268                 if (!asn1_octet_decode(ctx, &ch))
 269                         return 0;
 270
 271                 if (ch != 0x00) {
 272                         ctx->error = ASN1_ERR_DEC_EOC_MISMATCH;
 273                         return 0;
 274                 }
 275
 276                 if (!asn1_octet_decode(ctx, &ch))
 277                         return 0;
 278
 279                 if (ch != 0x00) {
 280                         ctx->error = ASN1_ERR_DEC_EOC_MISMATCH;
 281                         return 0;
 282                 }
 283                 return 1;
 284         } else {
 285                 if (ctx->pointer != eoc) {
 286                         ctx->error = ASN1_ERR_DEC_LENGTH_MISMATCH;
 287                         return 0;
 288                 }
 289                 return 1;
 290         }
 291 }
 292
 293 static unsigned char asn1_null_decode(struct asn1_ctx *ctx, unsigned char *eoc)
 294 {
 295         ctx->pointer = eoc;
 296         return 1;
 297 }
 298
 299 static unsigned char asn1_long_decode(struct asn1_ctx *ctx,
 300                                       unsigned char *eoc,
 301                                       long *integer)
 302 {
 303         unsigned char ch;
 304         unsigned int  len;
 305
 306         if (!asn1_octet_decode(ctx, &ch))
 307                 return 0;
 308
 309         *integer = (signed char) ch;
 310         len = 1;
 311
 312         while (ctx->pointer < eoc) {
 313                 if (++len > sizeof (long)) {
 314                         ctx->error = ASN1_ERR_DEC_BADVALUE;
 315                         return 0;
 316                 }
 317
 318                 if (!asn1_octet_decode(ctx, &ch))
 319                         return 0;
 320
 321                 *integer <<= 8;
 322                 *integer |= ch;
 323         }
 324         return 1;
 325 }
 326
 327 static unsigned char asn1_uint_decode(struct asn1_ctx *ctx,
 328                                       unsigned char *eoc,
 329                                       unsigned int *integer)
 330 {
 331         unsigned char ch;
 332         unsigned int  len;
 333
 334         if (!asn1_octet_decode(ctx, &ch))
 335                 return 0;
 336
 337         *integer = ch;
 338         if (ch == 0) len = 0;
 339         else len = 1;
 340
 341         while (ctx->pointer < eoc) {
 342                 if (++len > sizeof (unsigned int)) {
 343                         ctx->error = ASN1_ERR_DEC_BADVALUE;
 344                         return 0;
 345                 }
 346
 347                 if (!asn1_octet_decode(ctx, &ch))
 348                         return 0;
 349
 350                 *integer <<= 8;
 351                 *integer |= ch;
 352         }
 353         return 1;
 354 }
 355
 356 static unsigned char asn1_ulong_decode(struct asn1_ctx *ctx,
 357                                        unsigned char *eoc,
 358                                        unsigned long *integer)
 359 {
 360         unsigned char ch;
 361         unsigned int  len;
 362
 363         if (!asn1_octet_decode(ctx, &ch))
 364                 return 0;
 365
 366         *integer = ch;
 367         if (ch == 0) len = 0;
 368         else len = 1;
 369
 370         while (ctx->pointer < eoc) {
 371                 if (++len > sizeof (unsigned long)) {
 372                         ctx->error = ASN1_ERR_DEC_BADVALUE;
 373                         return 0;
 374                 }
 375
 376                 if (!asn1_octet_decode(ctx, &ch))
 377                         return 0;
 378
 379                 *integer <<= 8;
 380                 *integer |= ch;
 381         }
 382         return 1;
 383 }
 384
 385 static unsigned char asn1_octets_decode(struct asn1_ctx *ctx,
 386                                         unsigned char *eoc,
 387                                         unsigned char **octets,
 388                                         unsigned int *len)
 389 {
 390         unsigned char *ptr;
 391
 392         *len = 0;
 393
 394         *octets = kmalloc(eoc - ctx->pointer, GFP_ATOMIC);
 395         if (*octets == NULL) {
 396                 if (net_ratelimit())
 397                         printk("OOM in bsalg (%d)\n", __LINE__);
 398                 return 0;
 399         }
 400
 401         ptr = *octets;
 402         while (ctx->pointer < eoc) {
 403                 if (!asn1_octet_decode(ctx, (unsigned char *)ptr++)) {
 404                         kfree(*octets);
 405                         *octets = NULL;
 406                         return 0;
 407                 }
 408                 (*len)++;
 409         }
 410         return 1;
 411 }
 412
 413 static unsigned char asn1_subid_decode(struct asn1_ctx *ctx,
 414                                        unsigned long *subid)
 415 {
 416         unsigned char ch;
 417
 418         *subid = 0;
 419
 420         do {
 421                 if (!asn1_octet_decode(ctx, &ch))
 422                         return 0;
 423
 424                 *subid <<= 7;
 425                 *subid |= ch & 0x7F;
 426         } while ((ch & 0x80) == 0x80);
 427         return 1;
 428 }
 429
 430 static unsigned char asn1_oid_decode(struct asn1_ctx *ctx,
 431                                      unsigned char *eoc,
 432                                      unsigned long **oid,
 433                                      unsigned int *len)
 434 {
 435         unsigned long subid;
 436         unsigned int  size;
 437         unsigned long *optr;
 438
 439         size = eoc - ctx->pointer + 1;
 440         *oid = kmalloc(size * sizeof(unsigned long), GFP_ATOMIC);
 441         if (*oid == NULL) {
 442                 if (net_ratelimit())
 443                         printk("OOM in bsalg (%d)\n", __LINE__);
 444                 return 0;
 445         }
 446
 447         optr = *oid;
 448
 449         if (!asn1_subid_decode(ctx, &subid)) {
 450                 kfree(*oid);
 451                 *oid = NULL;
 452                 return 0;
 453         }
 454
 455         if (subid < 40) {
 456                 optr [0] = 0;
 457                 optr [1] = subid;
 458         } else if (subid < 80) {
 459                 optr [0] = 1;
 460                 optr [1] = subid - 40;
 461         } else {
 462                 optr [0] = 2;
 463                 optr [1] = subid - 80;
 464         }
 465
 466         *len = 2;
 467         optr += 2;
 468
 469         while (ctx->pointer < eoc) {
 470                 if (++(*len) > size) {
 471                         ctx->error = ASN1_ERR_DEC_BADVALUE;
 472                         kfree(*oid);
 473                         *oid = NULL;
 474                         return 0;
 475                 }
 476
 477                 if (!asn1_subid_decode(ctx, optr++)) {
 478                         kfree(*oid);
 479                         *oid = NULL;
 480                         return 0;
 481                 }
 482         }
 483         return 1;
 484 }
 485
 486 /*****************************************************************************
 487  *
 488  * SNMP decoding routines (gxsnmp author Dirk Wisse)
 489  *
 490  *****************************************************************************/
 491
 492 /* SNMP Versions */
 493 #define SNMP_V1                         0
 494 #define SNMP_V2C                        1
 495 #define SNMP_V2                         2
 496 #define SNMP_V3                         3
 497
 498 /* Default Sizes */
 499 #define SNMP_SIZE_COMM                  256
 500 #define SNMP_SIZE_OBJECTID              128
 501 #define SNMP_SIZE_BUFCHR                256
 502 #define SNMP_SIZE_BUFINT                128
 503 #define SNMP_SIZE_SMALLOBJECTID         16
 504
 505 /* Requests */
 506 #define SNMP_PDU_GET                    0
 507 #define SNMP_PDU_NEXT                   1
 508 #define SNMP_PDU_RESPONSE               2
 509 #define SNMP_PDU_SET                    3
 510 #define SNMP_PDU_TRAP1                  4
 511 #define SNMP_PDU_BULK                   5
 512 #define SNMP_PDU_INFORM                 6
 513 #define SNMP_PDU_TRAP2                  7
 514
 515 /* Errors */
 516 #define SNMP_NOERROR                    0
 517 #define SNMP_TOOBIG                     1
 518 #define SNMP_NOSUCHNAME                 2
 519 #define SNMP_BADVALUE                   3
 520 #define SNMP_READONLY                   4
 521 #define SNMP_GENERROR                   5
 522 #define SNMP_NOACCESS                   6
 523 #define SNMP_WRONGTYPE                  7
 524 #define SNMP_WRONGLENGTH                8
 525 #define SNMP_WRONGENCODING              9
 526 #define SNMP_WRONGVALUE                 10
 527 #define SNMP_NOCREATION                 11
 528 #define SNMP_INCONSISTENTVALUE          12
 529 #define SNMP_RESOURCEUNAVAILABLE        13
 530 #define SNMP_COMMITFAILED               14
 531 #define SNMP_UNDOFAILED                 15
 532 #define SNMP_AUTHORIZATIONERROR         16
 533 #define SNMP_NOTWRITABLE                17
 534 #define SNMP_INCONSISTENTNAME           18
 535
 536 /* General SNMP V1 Traps */
 537 #define SNMP_TRAP_COLDSTART             0
 538 #define SNMP_TRAP_WARMSTART             1
 539 #define SNMP_TRAP_LINKDOWN              2
 540 #define SNMP_TRAP_LINKUP                3
 541 #define SNMP_TRAP_AUTFAILURE            4
 542 #define SNMP_TRAP_EQPNEIGHBORLOSS       5
 543 #define SNMP_TRAP_ENTSPECIFIC           6
 544
 545 /* SNMPv1 Types */
 546 #define SNMP_NULL                0
 547 #define SNMP_INTEGER             1    /* l  */
 548 #define SNMP_OCTETSTR            2    /* c  */
 549 #define SNMP_DISPLAYSTR          2    /* c  */
 550 #define SNMP_OBJECTID            3    /* ul */
 551 #define SNMP_IPADDR              4    /* uc */
 552 #define SNMP_COUNTER             5    /* ul */
 553 #define SNMP_GAUGE               6    /* ul */
 554 #define SNMP_TIMETICKS           7    /* ul */
 555 #define SNMP_OPAQUE              8    /* c  */
 556
 557 /* Additional SNMPv2 Types */
 558 #define SNMP_UINTEGER            5    /* ul */
 559 #define SNMP_BITSTR              9    /* uc */
 560 #define SNMP_NSAP               10    /* uc */
 561 #define SNMP_COUNTER64          11    /* ul */
 562 #define SNMP_NOSUCHOBJECT       12
 563 #define SNMP_NOSUCHINSTANCE     13
 564 #define SNMP_ENDOFMIBVIEW       14
 565
 566 union snmp_syntax
 567 {
 568         unsigned char uc[0];    /* 8 bit unsigned */
 569         char c[0];              /* 8 bit signed */
 570         unsigned long ul[0];    /* 32 bit unsigned */
 571         long l[0];              /* 32 bit signed */
 572 };
 573
 574 struct snmp_object
 575 {
 576         unsigned long *id;
 577         unsigned int id_len;
 578         unsigned short type;
 579         unsigned int syntax_len;
 580         union snmp_syntax syntax;
 581 };
 582
 583 struct snmp_request
 584 {
 585         unsigned long id;
 586         unsigned int error_status;
 587         unsigned int error_index;
 588 };
 589
 590 struct snmp_v1_trap
 591 {
 592         unsigned long *id;
 593         unsigned int id_len;
 594         unsigned long ip_address;       /* pointer  */
 595         unsigned int general;
 596         unsigned int specific;
 597         unsigned long time;
 598 };
 599
 600 /* SNMP types */
 601 #define SNMP_IPA    0
 602 #define SNMP_CNT    1
 603 #define SNMP_GGE    2
 604 #define SNMP_TIT    3
 605 #define SNMP_OPQ    4
 606 #define SNMP_C64    6
 607
 608 /* SNMP errors */
 609 #define SERR_NSO    0
 610 #define SERR_NSI    1
 611 #define SERR_EOM    2
 612
 613 static inline void mangle_address(unsigned char *begin,
 614                                   unsigned char *addr,
 615                                   const struct oct1_map *map,
 616                                   __sum16 *check);
 617 struct snmp_cnv
 618 {
 619         unsigned int class;
 620         unsigned int tag;
 621         int syntax;
 622 };
 623
 624 static struct snmp_cnv snmp_conv [] =
 625 {
 626         {ASN1_UNI, ASN1_NUL, SNMP_NULL},
 627         {ASN1_UNI, ASN1_INT, SNMP_INTEGER},
 628         {ASN1_UNI, ASN1_OTS, SNMP_OCTETSTR},
 629         {ASN1_UNI, ASN1_OTS, SNMP_DISPLAYSTR},
 630         {ASN1_UNI, ASN1_OJI, SNMP_OBJECTID},
 631         {ASN1_APL, SNMP_IPA, SNMP_IPADDR},
 632         {ASN1_APL, SNMP_CNT, SNMP_COUNTER},     /* Counter32 */
 633         {ASN1_APL, SNMP_GGE, SNMP_GAUGE},       /* Gauge32 == Unsigned32  */
 634         {ASN1_APL, SNMP_TIT, SNMP_TIMETICKS},
 635         {ASN1_APL, SNMP_OPQ, SNMP_OPAQUE},
 636
 637         /* SNMPv2 data types and errors */
 638         {ASN1_UNI, ASN1_BTS, SNMP_BITSTR},
 639         {ASN1_APL, SNMP_C64, SNMP_COUNTER64},
 640         {ASN1_CTX, SERR_NSO, SNMP_NOSUCHOBJECT},
 641         {ASN1_CTX, SERR_NSI, SNMP_NOSUCHINSTANCE},
 642         {ASN1_CTX, SERR_EOM, SNMP_ENDOFMIBVIEW},
 643         {0,       0,       -1}
 644 };
 645
 646 static unsigned char snmp_tag_cls2syntax(unsigned int tag,
 647                                          unsigned int cls,
 648                                          unsigned short *syntax)
 649 {
 650         struct snmp_cnv *cnv;
 651
 652         cnv = snmp_conv;
 653
 654         while (cnv->syntax != -1) {
 655                 if (cnv->tag == tag && cnv->class == cls) {
 656                         *syntax = cnv->syntax;
 657                         return 1;
 658                 }
 659                 cnv++;
 660         }
 661         return 0;
 662 }
 663
 664 static unsigned char snmp_object_decode(struct asn1_ctx *ctx,
 665                                         struct snmp_object **obj)
 666 {
 667         unsigned int cls, con, tag, len, idlen;
 668         unsigned short type;
 669         unsigned char *eoc, *end, *p;
 670         unsigned long *lp, *id;
 671         unsigned long ul;
 672         long l;
 673
 674         *obj = NULL;
 675         id = NULL;
 676
 677         if (!asn1_header_decode(ctx, &eoc, &cls, &con, &tag))
 678                 return 0;
 679
 680         if (cls != ASN1_UNI || con != ASN1_CON || tag != ASN1_SEQ)
 681                 return 0;
 682
 683         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 684                 return 0;
 685
 686         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_OJI)
 687                 return 0;
 688
 689         if (!asn1_oid_decode(ctx, end, &id, &idlen))
 690                 return 0;
 691
 692         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag)) {
 693                 kfree(id);
 694                 return 0;
 695         }
 696
 697         if (con != ASN1_PRI) {
 698                 kfree(id);
 699                 return 0;
 700         }
 701
 702         type = 0;
 703         if (!snmp_tag_cls2syntax(tag, cls, &type)) {
 704                 kfree(id);
 705                 return 0;
 706         }
 707
 708         l = 0;
 709         switch (type) {
 710                 case SNMP_INTEGER:
 711                         len = sizeof(long);
 712                         if (!asn1_long_decode(ctx, end, &l)) {
 713                                 kfree(id);
 714                                 return 0;
 715                         }
 716                         *obj = kmalloc(sizeof(struct snmp_object) + len,
 717                                        GFP_ATOMIC);
 718                         if (*obj == NULL) {
 719                                 kfree(id);
 720                                 if (net_ratelimit())
 721                                         printk("OOM in bsalg (%d)\n", __LINE__);
 722                                 return 0;
 723                         }
 724                         (*obj)->syntax.l[0] = l;
 725                         break;
 726                 case SNMP_OCTETSTR:
 727                 case SNMP_OPAQUE:
 728                         if (!asn1_octets_decode(ctx, end, &p, &len)) {
 729                                 kfree(id);
 730                                 return 0;
 731                         }
 732                         *obj = kmalloc(sizeof(struct snmp_object) + len,
 733                                        GFP_ATOMIC);
 734                         if (*obj == NULL) {
 735                                 kfree(id);
 736                                 if (net_ratelimit())
 737                                         printk("OOM in bsalg (%d)\n", __LINE__);
 738                                 return 0;
 739                         }
 740                         memcpy((*obj)->syntax.c, p, len);
 741                         kfree(p);
 742                         break;
 743                 case SNMP_NULL:
 744                 case SNMP_NOSUCHOBJECT:
 745                 case SNMP_NOSUCHINSTANCE:
 746                 case SNMP_ENDOFMIBVIEW:
 747                         len = 0;
 748                         *obj = kmalloc(sizeof(struct snmp_object), GFP_ATOMIC);
 749                         if (*obj == NULL) {
 750                                 kfree(id);
 751                                 if (net_ratelimit())
 752                                         printk("OOM in bsalg (%d)\n", __LINE__);
 753                                 return 0;
 754                         }
 755                         if (!asn1_null_decode(ctx, end)) {
 756                                 kfree(id);
 757                                 kfree(*obj);
 758                                 *obj = NULL;
 759                                 return 0;
 760                         }
 761                         break;
 762                 case SNMP_OBJECTID:
 763                         if (!asn1_oid_decode(ctx, end, (unsigned long **)&lp, &len)) {
 764                                 kfree(id);
 765                                 return 0;
 766                         }
 767                         len *= sizeof(unsigned long);
 768                         *obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
 769                         if (*obj == NULL) {
 770                                 kfree(lp);
 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(__sum16 *csum,
 877                       const unsigned char *optr,
 878                       const unsigned char *nptr,
 879                       int offset)
 880 {
 881         unsigned char s[4];
 882
 883         if (offset & 1) {
 884                 s[0] = s[2] = 0;
 885                 s[1] = ~*optr;
 886                 s[3] = *nptr;
 887         } else {
 888                 s[1] = s[3] = 0;
 889                 s[0] = ~*optr;
 890                 s[2] = *nptr;
 891         }
 892
 893         *csum = csum_fold(csum_partial(s, 4, ~csum_unfold(*csum)));
 894 }
 895
 896 /*
 897  * Mangle IP address.
 898  *      - begin points to the start of the snmp messgae
 899  *      - addr points to the start of the address
 900  */
 901 static inline void mangle_address(unsigned char *begin,
 902                                   unsigned char *addr,
 903                                   const struct oct1_map *map,
 904                                   __sum16 *check)
 905 {
 906         if (map->from == NOCT1(addr)) {
 907                 u_int32_t old;
 908
 909                 if (debug)
 910                         memcpy(&old, (unsigned char *)addr, sizeof(old));
 911
 912                 *addr = map->to;
 913
 914                 /* Update UDP checksum if being used */
 915                 if (*check) {
 916                         fast_csum(check,
 917                                   &map->from, &map->to, addr - begin);
 918                 }
 919
 920                 if (debug)
 921                         printk(KERN_DEBUG "bsalg: mapped %u.%u.%u.%u to "
 922                                "%u.%u.%u.%u\n", NIPQUAD(old), NIPQUAD(*addr));
 923         }
 924 }
 925
 926 static unsigned char snmp_trap_decode(struct asn1_ctx *ctx,
 927                                       struct snmp_v1_trap *trap,
 928                                       const struct oct1_map *map,
 929                                       __sum16 *check)
 930 {
 931         unsigned int cls, con, tag, len;
 932         unsigned char *end;
 933
 934         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 935                 return 0;
 936
 937         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_OJI)
 938                 return 0;
 939
 940         if (!asn1_oid_decode(ctx, end, &trap->id, &trap->id_len))
 941                 return 0;
 942
 943         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 944                 goto err_id_free;
 945
 946         if (!((cls == ASN1_APL && con == ASN1_PRI && tag == SNMP_IPA) ||
 947               (cls == ASN1_UNI && con == ASN1_PRI && tag == ASN1_OTS)))
 948                 goto err_id_free;
 949
 950         if (!asn1_octets_decode(ctx, end, (unsigned char **)&trap->ip_address, &len))
 951                 goto err_id_free;
 952
 953         /* IPv4 only */
 954         if (len != 4)
 955                 goto err_addr_free;
 956
 957         mangle_address(ctx->begin, ctx->pointer - 4, map, check);
 958
 959         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 960                 goto err_addr_free;
 961
 962         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
 963                 goto err_addr_free;
 964
 965         if (!asn1_uint_decode(ctx, end, &trap->general))
 966                 goto err_addr_free;
 967
 968         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 969                 goto err_addr_free;
 970
 971         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
 972                 goto err_addr_free;
 973
 974         if (!asn1_uint_decode(ctx, end, &trap->specific))
 975                 goto err_addr_free;
 976
 977         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 978                 goto err_addr_free;
 979
 980         if (!((cls == ASN1_APL && con == ASN1_PRI && tag == SNMP_TIT) ||
 981               (cls == ASN1_UNI && con == ASN1_PRI && tag == ASN1_INT)))
 982                 goto err_addr_free;
 983
 984         if (!asn1_ulong_decode(ctx, end, &trap->time))
 985                 goto err_addr_free;
 986
 987         return 1;
 988
 989 err_addr_free:
 990         kfree((unsigned long *)trap->ip_address);
 991
 992 err_id_free:
 993         kfree(trap->id);
 994
 995         return 0;
 996 }
 997
 998 /*****************************************************************************
 999  *
1000  * Misc. routines
1001  *
1002  *****************************************************************************/
1003
1004 static void hex_dump(unsigned char *buf, size_t len)
1005 {
1006         size_t i;
1007
1008         for (i = 0; i < len; i++) {
1009                 if (i && !(i % 16))
1010                         printk("\n");
1011                 printk("%02x ", *(buf + i));
1012         }
1013         printk("\n");
1014 }
1015
1016 /*
1017  * Parse and mangle SNMP message according to mapping.
1018  * (And this is the fucking 'basic' method).
1019  */
1020 static int snmp_parse_mangle(unsigned char *msg,
1021                              u_int16_t len,
1022                              const struct oct1_map *map,
1023                              __sum16 *check)
1024 {
1025         unsigned char *eoc, *end;
1026         unsigned int cls, con, tag, vers, pdutype;
1027         struct asn1_ctx ctx;
1028         struct asn1_octstr comm;
1029         struct snmp_object **obj;
1030
1031         if (debug > 1)
1032                 hex_dump(msg, len);
1033
1034         asn1_open(&ctx, msg, len);
1035
1036         /*
1037          * Start of SNMP message.
1038          */
1039         if (!asn1_header_decode(&ctx, &eoc, &cls, &con, &tag))
1040                 return 0;
1041         if (cls != ASN1_UNI || con != ASN1_CON || tag != ASN1_SEQ)
1042                 return 0;
1043
1044         /*
1045          * Version 1 or 2 handled.
1046          */
1047         if (!asn1_header_decode(&ctx, &end, &cls, &con, &tag))
1048                 return 0;
1049         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
1050                 return 0;
1051         if (!asn1_uint_decode (&ctx, end, &vers))
1052                 return 0;
1053         if (debug > 1)
1054                 printk(KERN_DEBUG "bsalg: snmp version: %u\n", vers + 1);
1055         if (vers > 1)
1056                 return 1;
1057
1058         /*
1059          * Community.
1060          */
1061         if (!asn1_header_decode (&ctx, &end, &cls, &con, &tag))
1062                 return 0;
1063         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_OTS)
1064                 return 0;
1065         if (!asn1_octets_decode(&ctx, end, &comm.data, &comm.len))
1066                 return 0;
1067         if (debug > 1) {
1068                 unsigned int i;
1069
1070                 printk(KERN_DEBUG "bsalg: community: ");
1071                 for (i = 0; i < comm.len; i++)
1072                         printk("%c", comm.data[i]);
1073                 printk("\n");
1074         }
1075         kfree(comm.data);
1076
1077         /*
1078          * PDU type
1079          */
1080         if (!asn1_header_decode(&ctx, &eoc, &cls, &con, &pdutype))
1081                 return 0;
1082         if (cls != ASN1_CTX || con != ASN1_CON)
1083                 return 0;
1084         if (debug > 1) {
1085                 unsigned char *pdus[] = {
1086                         [SNMP_PDU_GET] = "get",
1087                         [SNMP_PDU_NEXT] = "get-next",
1088                         [SNMP_PDU_RESPONSE] = "response",
1089                         [SNMP_PDU_SET] = "set",
1090                         [SNMP_PDU_TRAP1] = "trapv1",
1091                         [SNMP_PDU_BULK] = "bulk",
1092                         [SNMP_PDU_INFORM] = "inform",
1093                         [SNMP_PDU_TRAP2] = "trapv2"
1094                 };
1095
1096                 if (pdutype > SNMP_PDU_TRAP2)
1097                         printk(KERN_DEBUG "bsalg: bad pdu type %u\n", pdutype);
1098                 else
1099                         printk(KERN_DEBUG "bsalg: pdu: %s\n", pdus[pdutype]);
1100         }
1101         if (pdutype != SNMP_PDU_RESPONSE &&
1102             pdutype != SNMP_PDU_TRAP1 && pdutype != SNMP_PDU_TRAP2)
1103                 return 1;
1104
1105         /*
1106          * Request header or v1 trap
1107          */
1108         if (pdutype == SNMP_PDU_TRAP1) {
1109                 struct snmp_v1_trap trap;
1110                 unsigned char ret = snmp_trap_decode(&ctx, &trap, map, check);
1111
1112                 if (ret) {
1113                         kfree(trap.id);
1114                         kfree((unsigned long *)trap.ip_address);
1115                 } else
1116                         return ret;
1117
1118         } else {
1119                 struct snmp_request req;
1120
1121                 if (!snmp_request_decode(&ctx, &req))
1122                         return 0;
1123
1124                 if (debug > 1)
1125                         printk(KERN_DEBUG "bsalg: request: id=0x%lx error_status=%u "
1126                         "error_index=%u\n", req.id, req.error_status,
1127                         req.error_index);
1128         }
1129
1130         /*
1131          * Loop through objects, look for IP addresses to mangle.
1132          */
1133         if (!asn1_header_decode(&ctx, &eoc, &cls, &con, &tag))
1134                 return 0;
1135
1136         if (cls != ASN1_UNI || con != ASN1_CON || tag != ASN1_SEQ)
1137                 return 0;
1138
1139         obj = kmalloc(sizeof(struct snmp_object), GFP_ATOMIC);
1140         if (obj == NULL) {
1141                 if (net_ratelimit())
1142                         printk(KERN_WARNING "OOM in bsalg(%d)\n", __LINE__);
1143                 return 0;
1144         }
1145
1146         while (!asn1_eoc_decode(&ctx, eoc)) {
1147                 unsigned int i;
1148
1149                 if (!snmp_object_decode(&ctx, obj)) {
1150                         if (*obj) {
1151                                 kfree((*obj)->id);
1152                                 kfree(*obj);
1153                         }
1154                         kfree(obj);
1155                         return 0;
1156                 }
1157
1158                 if (debug > 1) {
1159                         printk(KERN_DEBUG "bsalg: object: ");
1160                         for (i = 0; i < (*obj)->id_len; i++) {
1161                                 if (i > 0)
1162                                         printk(".");
1163                                 printk("%lu", (*obj)->id[i]);
1164                         }
1165                         printk(": type=%u\n", (*obj)->type);
1166
1167                 }
1168
1169                 if ((*obj)->type == SNMP_IPADDR)
1170                         mangle_address(ctx.begin, ctx.pointer - 4 , map, check);
1171
1172                 kfree((*obj)->id);
1173                 kfree(*obj);
1174         }
1175         kfree(obj);
1176
1177         if (!asn1_eoc_decode(&ctx, eoc))
1178                 return 0;
1179
1180         return 1;
1181 }
1182
1183 /*****************************************************************************
1184  *
1185  * NAT routines.
1186  *
1187  *****************************************************************************/
1188
1189 /*
1190  * SNMP translation routine.
1191  */
1192 static int snmp_translate(struct ip_conntrack *ct,
1193                           enum ip_conntrack_info ctinfo,
1194                           struct sk_buff **pskb)
1195 {
1196         struct iphdr *iph = (*pskb)->nh.iph;
1197         struct udphdr *udph = (struct udphdr *)((__be32 *)iph + iph->ihl);
1198         u_int16_t udplen = ntohs(udph->len);
1199         u_int16_t paylen = udplen - sizeof(struct udphdr);
1200         int dir = CTINFO2DIR(ctinfo);
1201         struct oct1_map map;
1202
1203         /*
1204          * Determine mappping for application layer addresses based
1205          * on NAT manipulations for the packet.
1206          */
1207         if (dir == IP_CT_DIR_ORIGINAL) {
1208                 /* SNAT traps */
1209                 map.from = NOCT1(&ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.ip);
1210                 map.to = NOCT1(&ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.ip);
1211         } else {
1212                 /* DNAT replies */
1213                 map.from = NOCT1(&ct->tuplehash[IP_CT_DIR_REPLY].tuple.src.ip);
1214                 map.to = NOCT1(&ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.dst.ip);
1215         }
1216
1217         if (map.from == map.to)
1218                 return NF_ACCEPT;
1219
1220         if (!snmp_parse_mangle((unsigned char *)udph + sizeof(struct udphdr),
1221                                paylen, &map, &udph->check)) {
1222                 if (net_ratelimit())
1223                         printk(KERN_WARNING "bsalg: parser failed\n");
1224                 return NF_DROP;
1225         }
1226         return NF_ACCEPT;
1227 }
1228
1229 /* We don't actually set up expectations, just adjust internal IP
1230  * addresses if this is being NATted */
1231 static int help(struct sk_buff **pskb,
1232                 struct ip_conntrack *ct,
1233                 enum ip_conntrack_info ctinfo)
1234 {
1235         int dir = CTINFO2DIR(ctinfo);
1236         unsigned int ret;
1237         struct iphdr *iph = (*pskb)->nh.iph;
1238         struct udphdr *udph = (struct udphdr *)((u_int32_t *)iph + iph->ihl);
1239
1240         /* SNMP replies and originating SNMP traps get mangled */
1241         if (udph->source == htons(SNMP_PORT) && dir != IP_CT_DIR_REPLY)
1242                 return NF_ACCEPT;
1243         if (udph->dest == htons(SNMP_TRAP_PORT) && dir != IP_CT_DIR_ORIGINAL)
1244                 return NF_ACCEPT;
1245
1246         /* No NAT? */
1247         if (!(ct->status & IPS_NAT_MASK))
1248                 return NF_ACCEPT;
1249
1250         /*
1251          * Make sure the packet length is ok.  So far, we were only guaranteed
1252          * to have a valid length IP header plus 8 bytes, which means we have
1253          * enough room for a UDP header.  Just verify the UDP length field so we
1254          * can mess around with the payload.
1255          */
1256         if (ntohs(udph->len) != (*pskb)->len - (iph->ihl << 2)) {
1257                  if (net_ratelimit())
1258                          printk(KERN_WARNING "SNMP: dropping malformed packet "
1259                                 "src=%u.%u.%u.%u dst=%u.%u.%u.%u\n",
1260                                 NIPQUAD(iph->saddr), NIPQUAD(iph->daddr));
1261                  return NF_DROP;
1262         }
1263
1264         if (!skb_make_writable(pskb, (*pskb)->len))
1265                 return NF_DROP;
1266
1267         spin_lock_bh(&snmp_lock);
1268         ret = snmp_translate(ct, ctinfo, pskb);
1269         spin_unlock_bh(&snmp_lock);
1270         return ret;
1271 }
1272
1273 static struct ip_conntrack_helper snmp_helper = {
1274         .max_expected = 0,
1275         .timeout = 180,
1276         .me = THIS_MODULE,
1277         .help = help,
1278         .name = "snmp",
1279
1280         .tuple = {.src = {.u = {.udp = {.port = __constant_htons(SNMP_PORT)}}},
1281                   .dst = {.protonum = IPPROTO_UDP},
1282         },
1283         .mask = {.src = {.u = {0xFFFF}},
1284                  .dst = {.protonum = 0xFF},
1285         },
1286 };
1287
1288 static struct ip_conntrack_helper snmp_trap_helper = {
1289         .max_expected = 0,
1290         .timeout = 180,
1291         .me = THIS_MODULE,
1292         .help = help,
1293         .name = "snmp_trap",
1294
1295         .tuple = {.src = {.u = {.udp = {.port = __constant_htons(SNMP_TRAP_PORT)}}},
1296                   .dst = {.protonum = IPPROTO_UDP},
1297         },
1298         .mask = {.src = {.u = {0xFFFF}},
1299                  .dst = {.protonum = 0xFF},
1300         },
1301 };
1302
1303 /*****************************************************************************
1304  *
1305  * Module stuff.
1306  *
1307  *****************************************************************************/
1308
1309 static int __init ip_nat_snmp_basic_init(void)
1310 {
1311         int ret = 0;
1312
1313         ret = ip_conntrack_helper_register(&snmp_helper);
1314         if (ret < 0)
1315                 return ret;
1316         ret = ip_conntrack_helper_register(&snmp_trap_helper);
1317         if (ret < 0) {
1318                 ip_conntrack_helper_unregister(&snmp_helper);
1319                 return ret;
1320         }
1321         return ret;
1322 }
1323
1324 static void __exit ip_nat_snmp_basic_fini(void)
1325 {
1326         ip_conntrack_helper_unregister(&snmp_helper);
1327         ip_conntrack_helper_unregister(&snmp_trap_helper);
1328 }
1329
1330 module_init(ip_nat_snmp_basic_init);
1331 module_exit(ip_nat_snmp_basic_fini);
1332
1333 module_param(debug, int, 0600);