net/ipv4/netfilter/nf_nat_snmp_basic.c

   1 /*
   2  * nf_nat_snmp_basic.c
   3  *
   4  * Basic SNMP Application Layer Gateway
   5  *
   6  * This IP NAT module is intended for use with SNMP network
   7  * discovery and monitoring applications where target networks use
   8  * conflicting private address realms.
   9  *
  10  * Static NAT is used to remap the networks from the view of the network
  11  * management system at the IP layer, and this module remaps some application
  12  * layer addresses to match.
  13  *
  14  * The simplest form of ALG is performed, where only tagged IP addresses
  15  * are modified.  The module does not need to be MIB aware and only scans
  16  * messages at the ASN.1/BER level.
  17  *
  18  * Currently, only SNMPv1 and SNMPv2 are supported.
  19  *
  20  * More information on ALG and associated issues can be found in
  21  * RFC 2962
  22  *
  23  * The ASB.1/BER parsing code is derived from the gxsnmp package by Gregory
  24  * McLean & Jochen Friedrich, stripped down for use in the kernel.
  25  *
  26  * Copyright (c) 2000 RP Internet (www.rpi.net.au).
  27  *
  28  * This program is free software; you can redistribute it and/or modify
  29  * it under the terms of the GNU General Public License as published by
  30  * the Free Software Foundation; either version 2 of the License, or
  31  * (at your option) any later version.
  32  * This program is distributed in the hope that it will be useful,
  33  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  34  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  35  * GNU General Public License for more details.
  36  * You should have received a copy of the GNU General Public License
  37  * along with this program; if not, write to the Free Software
  38  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
  39  *
  40  * Author: James Morris <jmorris@intercode.com.au>
  41  */
  42 #include <linux/module.h>
  43 #include <linux/moduleparam.h>
  44 #include <linux/types.h>
  45 #include <linux/kernel.h>
  46 #include <linux/in.h>
  47 #include <linux/ip.h>
  48 #include <linux/udp.h>
  49 #include <net/checksum.h>
  50 #include <net/udp.h>
  51
  52 #include <net/netfilter/nf_nat.h>
  53 #include <net/netfilter/nf_conntrack_expect.h>
  54 #include <net/netfilter/nf_conntrack_helper.h>
  55 #include <net/netfilter/nf_nat_helper.h>
  56
  57 MODULE_LICENSE("GPL");
  58 MODULE_AUTHOR("James Morris <jmorris@intercode.com.au>");
  59 MODULE_DESCRIPTION("Basic SNMP Application Layer Gateway");
  60 MODULE_ALIAS("ip_nat_snmp_basic");
  61
  62 #define SNMP_PORT 161
  63 #define SNMP_TRAP_PORT 162
  64 #define NOCT1(n) (*(u8 *)(n))
  65
  66 static int debug;
  67 static DEFINE_SPINLOCK(snmp_lock);
  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
 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
 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
 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
 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
 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 = 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         return 1;
 236 }
 237
 238 static unsigned char asn1_header_decode(struct asn1_ctx *ctx,
 239                                         unsigned char **eoc,
 240                                         unsigned int *cls,
 241                                         unsigned int *con,
 242                                         unsigned int *tag)
 243 {
 244         unsigned int def, len;
 245
 246         if (!asn1_id_decode(ctx, cls, con, tag))
 247                 return 0;
 248
 249         def = len = 0;
 250         if (!asn1_length_decode(ctx, &def, &len))
 251                 return 0;
 252
 253         if (def)
 254                 *eoc = ctx->pointer + len;
 255         else
 256                 *eoc = NULL;
 257         return 1;
 258 }
 259
 260 static unsigned char asn1_eoc_decode(struct asn1_ctx *ctx, unsigned char *eoc)
 261 {
 262         unsigned char ch;
 263
 264         if (eoc == NULL) {
 265                 if (!asn1_octet_decode(ctx, &ch))
 266                         return 0;
 267
 268                 if (ch != 0x00) {
 269                         ctx->error = ASN1_ERR_DEC_EOC_MISMATCH;
 270                         return 0;
 271                 }
 272
 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                 return 1;
 281         } else {
 282                 if (ctx->pointer != eoc) {
 283                         ctx->error = ASN1_ERR_DEC_LENGTH_MISMATCH;
 284                         return 0;
 285                 }
 286                 return 1;
 287         }
 288 }
 289
 290 static unsigned char asn1_null_decode(struct asn1_ctx *ctx, unsigned char *eoc)
 291 {
 292         ctx->pointer = eoc;
 293         return 1;
 294 }
 295
 296 static unsigned char asn1_long_decode(struct asn1_ctx *ctx,
 297                                       unsigned char *eoc,
 298                                       long *integer)
 299 {
 300         unsigned char ch;
 301         unsigned int  len;
 302
 303         if (!asn1_octet_decode(ctx, &ch))
 304                 return 0;
 305
 306         *integer = (signed char) ch;
 307         len = 1;
 308
 309         while (ctx->pointer < eoc) {
 310                 if (++len > sizeof (long)) {
 311                         ctx->error = ASN1_ERR_DEC_BADVALUE;
 312                         return 0;
 313                 }
 314
 315                 if (!asn1_octet_decode(ctx, &ch))
 316                         return 0;
 317
 318                 *integer <<= 8;
 319                 *integer |= ch;
 320         }
 321         return 1;
 322 }
 323
 324 static unsigned char asn1_uint_decode(struct asn1_ctx *ctx,
 325                                       unsigned char *eoc,
 326                                       unsigned int *integer)
 327 {
 328         unsigned char ch;
 329         unsigned int  len;
 330
 331         if (!asn1_octet_decode(ctx, &ch))
 332                 return 0;
 333
 334         *integer = ch;
 335         if (ch == 0) len = 0;
 336         else len = 1;
 337
 338         while (ctx->pointer < eoc) {
 339                 if (++len > sizeof (unsigned int)) {
 340                         ctx->error = ASN1_ERR_DEC_BADVALUE;
 341                         return 0;
 342                 }
 343
 344                 if (!asn1_octet_decode(ctx, &ch))
 345                         return 0;
 346
 347                 *integer <<= 8;
 348                 *integer |= ch;
 349         }
 350         return 1;
 351 }
 352
 353 static unsigned char asn1_ulong_decode(struct asn1_ctx *ctx,
 354                                        unsigned char *eoc,
 355                                        unsigned long *integer)
 356 {
 357         unsigned char ch;
 358         unsigned int  len;
 359
 360         if (!asn1_octet_decode(ctx, &ch))
 361                 return 0;
 362
 363         *integer = ch;
 364         if (ch == 0) len = 0;
 365         else len = 1;
 366
 367         while (ctx->pointer < eoc) {
 368                 if (++len > sizeof (unsigned long)) {
 369                         ctx->error = ASN1_ERR_DEC_BADVALUE;
 370                         return 0;
 371                 }
 372
 373                 if (!asn1_octet_decode(ctx, &ch))
 374                         return 0;
 375
 376                 *integer <<= 8;
 377                 *integer |= ch;
 378         }
 379         return 1;
 380 }
 381
 382 static unsigned char asn1_octets_decode(struct asn1_ctx *ctx,
 383                                         unsigned char *eoc,
 384                                         unsigned char **octets,
 385                                         unsigned int *len)
 386 {
 387         unsigned char *ptr;
 388
 389         *len = 0;
 390
 391         *octets = kmalloc(eoc - ctx->pointer, GFP_ATOMIC);
 392         if (*octets == NULL) {
 393                 if (net_ratelimit())
 394                         printk("OOM in bsalg (%d)\n", __LINE__);
 395                 return 0;
 396         }
 397
 398         ptr = *octets;
 399         while (ctx->pointer < eoc) {
 400                 if (!asn1_octet_decode(ctx, (unsigned char *)ptr++)) {
 401                         kfree(*octets);
 402                         *octets = NULL;
 403                         return 0;
 404                 }
 405                 (*len)++;
 406         }
 407         return 1;
 408 }
 409
 410 static unsigned char asn1_subid_decode(struct asn1_ctx *ctx,
 411                                        unsigned long *subid)
 412 {
 413         unsigned char ch;
 414
 415         *subid = 0;
 416
 417         do {
 418                 if (!asn1_octet_decode(ctx, &ch))
 419                         return 0;
 420
 421                 *subid <<= 7;
 422                 *subid |= ch & 0x7F;
 423         } while ((ch & 0x80) == 0x80);
 424         return 1;
 425 }
 426
 427 static unsigned char asn1_oid_decode(struct asn1_ctx *ctx,
 428                                      unsigned char *eoc,
 429                                      unsigned long **oid,
 430                                      unsigned int *len)
 431 {
 432         unsigned long subid;
 433         unsigned int  size;
 434         unsigned long *optr;
 435
 436         size = eoc - ctx->pointer + 1;
 437         *oid = kmalloc(size * sizeof(unsigned long), GFP_ATOMIC);
 438         if (*oid == NULL) {
 439                 if (net_ratelimit())
 440                         printk("OOM in bsalg (%d)\n", __LINE__);
 441                 return 0;
 442         }
 443
 444         optr = *oid;
 445
 446         if (!asn1_subid_decode(ctx, &subid)) {
 447                 kfree(*oid);
 448                 *oid = NULL;
 449                 return 0;
 450         }
 451
 452         if (subid < 40) {
 453                 optr [0] = 0;
 454                 optr [1] = subid;
 455         } else if (subid < 80) {
 456                 optr [0] = 1;
 457                 optr [1] = subid - 40;
 458         } else {
 459                 optr [0] = 2;
 460                 optr [1] = subid - 80;
 461         }
 462
 463         *len = 2;
 464         optr += 2;
 465
 466         while (ctx->pointer < eoc) {
 467                 if (++(*len) > size) {
 468                         ctx->error = ASN1_ERR_DEC_BADVALUE;
 469                         kfree(*oid);
 470                         *oid = NULL;
 471                         return 0;
 472                 }
 473
 474                 if (!asn1_subid_decode(ctx, optr++)) {
 475                         kfree(*oid);
 476                         *oid = NULL;
 477                         return 0;
 478                 }
 479         }
 480         return 1;
 481 }
 482
 483 /*****************************************************************************
 484  *
 485  * SNMP decoding routines (gxsnmp author Dirk Wisse)
 486  *
 487  *****************************************************************************/
 488
 489 /* SNMP Versions */
 490 #define SNMP_V1                         0
 491 #define SNMP_V2C                        1
 492 #define SNMP_V2                         2
 493 #define SNMP_V3                         3
 494
 495 /* Default Sizes */
 496 #define SNMP_SIZE_COMM                  256
 497 #define SNMP_SIZE_OBJECTID              128
 498 #define SNMP_SIZE_BUFCHR                256
 499 #define SNMP_SIZE_BUFINT                128
 500 #define SNMP_SIZE_SMALLOBJECTID         16
 501
 502 /* Requests */
 503 #define SNMP_PDU_GET                    0
 504 #define SNMP_PDU_NEXT                   1
 505 #define SNMP_PDU_RESPONSE               2
 506 #define SNMP_PDU_SET                    3
 507 #define SNMP_PDU_TRAP1                  4
 508 #define SNMP_PDU_BULK                   5
 509 #define SNMP_PDU_INFORM                 6
 510 #define SNMP_PDU_TRAP2                  7
 511
 512 /* Errors */
 513 #define SNMP_NOERROR                    0
 514 #define SNMP_TOOBIG                     1
 515 #define SNMP_NOSUCHNAME                 2
 516 #define SNMP_BADVALUE                   3
 517 #define SNMP_READONLY                   4
 518 #define SNMP_GENERROR                   5
 519 #define SNMP_NOACCESS                   6
 520 #define SNMP_WRONGTYPE                  7
 521 #define SNMP_WRONGLENGTH                8
 522 #define SNMP_WRONGENCODING              9
 523 #define SNMP_WRONGVALUE                 10
 524 #define SNMP_NOCREATION                 11
 525 #define SNMP_INCONSISTENTVALUE          12
 526 #define SNMP_RESOURCEUNAVAILABLE        13
 527 #define SNMP_COMMITFAILED               14
 528 #define SNMP_UNDOFAILED                 15
 529 #define SNMP_AUTHORIZATIONERROR         16
 530 #define SNMP_NOTWRITABLE                17
 531 #define SNMP_INCONSISTENTNAME           18
 532
 533 /* General SNMP V1 Traps */
 534 #define SNMP_TRAP_COLDSTART             0
 535 #define SNMP_TRAP_WARMSTART             1
 536 #define SNMP_TRAP_LINKDOWN              2
 537 #define SNMP_TRAP_LINKUP                3
 538 #define SNMP_TRAP_AUTFAILURE            4
 539 #define SNMP_TRAP_EQPNEIGHBORLOSS       5
 540 #define SNMP_TRAP_ENTSPECIFIC           6
 541
 542 /* SNMPv1 Types */
 543 #define SNMP_NULL                0
 544 #define SNMP_INTEGER             1    /* l  */
 545 #define SNMP_OCTETSTR            2    /* c  */
 546 #define SNMP_DISPLAYSTR          2    /* c  */
 547 #define SNMP_OBJECTID            3    /* ul */
 548 #define SNMP_IPADDR              4    /* uc */
 549 #define SNMP_COUNTER             5    /* ul */
 550 #define SNMP_GAUGE               6    /* ul */
 551 #define SNMP_TIMETICKS           7    /* ul */
 552 #define SNMP_OPAQUE              8    /* c  */
 553
 554 /* Additional SNMPv2 Types */
 555 #define SNMP_UINTEGER            5    /* ul */
 556 #define SNMP_BITSTR              9    /* uc */
 557 #define SNMP_NSAP               10    /* uc */
 558 #define SNMP_COUNTER64          11    /* ul */
 559 #define SNMP_NOSUCHOBJECT       12
 560 #define SNMP_NOSUCHINSTANCE     13
 561 #define SNMP_ENDOFMIBVIEW       14
 562
 563 union snmp_syntax
 564 {
 565         unsigned char uc[0];    /* 8 bit unsigned */
 566         char c[0];              /* 8 bit signed */
 567         unsigned long ul[0];    /* 32 bit unsigned */
 568         long l[0];              /* 32 bit signed */
 569 };
 570
 571 struct snmp_object
 572 {
 573         unsigned long *id;
 574         unsigned int id_len;
 575         unsigned short type;
 576         unsigned int syntax_len;
 577         union snmp_syntax syntax;
 578 };
 579
 580 struct snmp_request
 581 {
 582         unsigned long id;
 583         unsigned int error_status;
 584         unsigned int error_index;
 585 };
 586
 587 struct snmp_v1_trap
 588 {
 589         unsigned long *id;
 590         unsigned int id_len;
 591         unsigned long ip_address;       /* pointer  */
 592         unsigned int general;
 593         unsigned int specific;
 594         unsigned long time;
 595 };
 596
 597 /* SNMP types */
 598 #define SNMP_IPA    0
 599 #define SNMP_CNT    1
 600 #define SNMP_GGE    2
 601 #define SNMP_TIT    3
 602 #define SNMP_OPQ    4
 603 #define SNMP_C64    6
 604
 605 /* SNMP errors */
 606 #define SERR_NSO    0
 607 #define SERR_NSI    1
 608 #define SERR_EOM    2
 609
 610 static inline void mangle_address(unsigned char *begin,
 611                                   unsigned char *addr,
 612                                   const struct oct1_map *map,
 613                                   __sum16 *check);
 614 struct snmp_cnv
 615 {
 616         unsigned int class;
 617         unsigned int tag;
 618         int syntax;
 619 };
 620
 621 static const struct snmp_cnv snmp_conv[] = {
 622         {ASN1_UNI, ASN1_NUL, SNMP_NULL},
 623         {ASN1_UNI, ASN1_INT, SNMP_INTEGER},
 624         {ASN1_UNI, ASN1_OTS, SNMP_OCTETSTR},
 625         {ASN1_UNI, ASN1_OTS, SNMP_DISPLAYSTR},
 626         {ASN1_UNI, ASN1_OJI, SNMP_OBJECTID},
 627         {ASN1_APL, SNMP_IPA, SNMP_IPADDR},
 628         {ASN1_APL, SNMP_CNT, SNMP_COUNTER},     /* Counter32 */
 629         {ASN1_APL, SNMP_GGE, SNMP_GAUGE},       /* Gauge32 == Unsigned32  */
 630         {ASN1_APL, SNMP_TIT, SNMP_TIMETICKS},
 631         {ASN1_APL, SNMP_OPQ, SNMP_OPAQUE},
 632
 633         /* SNMPv2 data types and errors */
 634         {ASN1_UNI, ASN1_BTS, SNMP_BITSTR},
 635         {ASN1_APL, SNMP_C64, SNMP_COUNTER64},
 636         {ASN1_CTX, SERR_NSO, SNMP_NOSUCHOBJECT},
 637         {ASN1_CTX, SERR_NSI, SNMP_NOSUCHINSTANCE},
 638         {ASN1_CTX, SERR_EOM, SNMP_ENDOFMIBVIEW},
 639         {0,       0,       -1}
 640 };
 641
 642 static unsigned char snmp_tag_cls2syntax(unsigned int tag,
 643                                          unsigned int cls,
 644                                          unsigned short *syntax)
 645 {
 646         const struct snmp_cnv *cnv;
 647
 648         cnv = snmp_conv;
 649
 650         while (cnv->syntax != -1) {
 651                 if (cnv->tag == tag && cnv->class == cls) {
 652                         *syntax = cnv->syntax;
 653                         return 1;
 654                 }
 655                 cnv++;
 656         }
 657         return 0;
 658 }
 659
 660 static unsigned char snmp_object_decode(struct asn1_ctx *ctx,
 661                                         struct snmp_object **obj)
 662 {
 663         unsigned int cls, con, tag, len, idlen;
 664         unsigned short type;
 665         unsigned char *eoc, *end, *p;
 666         unsigned long *lp, *id;
 667         unsigned long ul;
 668         long l;
 669
 670         *obj = NULL;
 671         id = NULL;
 672
 673         if (!asn1_header_decode(ctx, &eoc, &cls, &con, &tag))
 674                 return 0;
 675
 676         if (cls != ASN1_UNI || con != ASN1_CON || tag != ASN1_SEQ)
 677                 return 0;
 678
 679         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 680                 return 0;
 681
 682         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_OJI)
 683                 return 0;
 684
 685         if (!asn1_oid_decode(ctx, end, &id, &idlen))
 686                 return 0;
 687
 688         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag)) {
 689                 kfree(id);
 690                 return 0;
 691         }
 692
 693         if (con != ASN1_PRI) {
 694                 kfree(id);
 695                 return 0;
 696         }
 697
 698         type = 0;
 699         if (!snmp_tag_cls2syntax(tag, cls, &type)) {
 700                 kfree(id);
 701                 return 0;
 702         }
 703
 704         l = 0;
 705         switch (type) {
 706                 case SNMP_INTEGER:
 707                         len = sizeof(long);
 708                         if (!asn1_long_decode(ctx, end, &l)) {
 709                                 kfree(id);
 710                                 return 0;
 711                         }
 712                         *obj = kmalloc(sizeof(struct snmp_object) + len,
 713                                        GFP_ATOMIC);
 714                         if (*obj == NULL) {
 715                                 kfree(id);
 716                                 if (net_ratelimit())
 717                                         printk("OOM in bsalg (%d)\n", __LINE__);
 718                                 return 0;
 719                         }
 720                         (*obj)->syntax.l[0] = l;
 721                         break;
 722                 case SNMP_OCTETSTR:
 723                 case SNMP_OPAQUE:
 724                         if (!asn1_octets_decode(ctx, end, &p, &len)) {
 725                                 kfree(id);
 726                                 return 0;
 727                         }
 728                         *obj = kmalloc(sizeof(struct snmp_object) + len,
 729                                        GFP_ATOMIC);
 730                         if (*obj == NULL) {
 731                                 kfree(id);
 732                                 if (net_ratelimit())
 733                                         printk("OOM in bsalg (%d)\n", __LINE__);
 734                                 return 0;
 735                         }
 736                         memcpy((*obj)->syntax.c, p, len);
 737                         kfree(p);
 738                         break;
 739                 case SNMP_NULL:
 740                 case SNMP_NOSUCHOBJECT:
 741                 case SNMP_NOSUCHINSTANCE:
 742                 case SNMP_ENDOFMIBVIEW:
 743                         len = 0;
 744                         *obj = kmalloc(sizeof(struct snmp_object), GFP_ATOMIC);
 745                         if (*obj == NULL) {
 746                                 kfree(id);
 747                                 if (net_ratelimit())
 748                                         printk("OOM in bsalg (%d)\n", __LINE__);
 749                                 return 0;
 750                         }
 751                         if (!asn1_null_decode(ctx, end)) {
 752                                 kfree(id);
 753                                 kfree(*obj);
 754                                 *obj = NULL;
 755                                 return 0;
 756                         }
 757                         break;
 758                 case SNMP_OBJECTID:
 759                         if (!asn1_oid_decode(ctx, end, (unsigned long **)&lp, &len)) {
 760                                 kfree(id);
 761                                 return 0;
 762                         }
 763                         len *= sizeof(unsigned long);
 764                         *obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
 765                         if (*obj == NULL) {
 766                                 kfree(lp);
 767                                 kfree(id);
 768                                 if (net_ratelimit())
 769                                         printk("OOM in bsalg (%d)\n", __LINE__);
 770                                 return 0;
 771                         }
 772                         memcpy((*obj)->syntax.ul, lp, len);
 773                         kfree(lp);
 774                         break;
 775                 case SNMP_IPADDR:
 776                         if (!asn1_octets_decode(ctx, end, &p, &len)) {
 777                                 kfree(id);
 778                                 return 0;
 779                         }
 780                         if (len != 4) {
 781                                 kfree(p);
 782                                 kfree(id);
 783                                 return 0;
 784                         }
 785                         *obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
 786                         if (*obj == NULL) {
 787                                 kfree(p);
 788                                 kfree(id);
 789                                 if (net_ratelimit())
 790                                         printk("OOM in bsalg (%d)\n", __LINE__);
 791                                 return 0;
 792                         }
 793                         memcpy((*obj)->syntax.uc, p, len);
 794                         kfree(p);
 795                         break;
 796                 case SNMP_COUNTER:
 797                 case SNMP_GAUGE:
 798                 case SNMP_TIMETICKS:
 799                         len = sizeof(unsigned long);
 800                         if (!asn1_ulong_decode(ctx, end, &ul)) {
 801                                 kfree(id);
 802                                 return 0;
 803                         }
 804                         *obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
 805                         if (*obj == NULL) {
 806                                 kfree(id);
 807                                 if (net_ratelimit())
 808                                         printk("OOM in bsalg (%d)\n", __LINE__);
 809                                 return 0;
 810                         }
 811                         (*obj)->syntax.ul[0] = ul;
 812                         break;
 813                 default:
 814                         kfree(id);
 815                         return 0;
 816         }
 817
 818         (*obj)->syntax_len = len;
 819         (*obj)->type = type;
 820         (*obj)->id = id;
 821         (*obj)->id_len = idlen;
 822
 823         if (!asn1_eoc_decode(ctx, eoc)) {
 824                 kfree(id);
 825                 kfree(*obj);
 826                 *obj = NULL;
 827                 return 0;
 828         }
 829         return 1;
 830 }
 831
 832 static unsigned char snmp_request_decode(struct asn1_ctx *ctx,
 833                                          struct snmp_request *request)
 834 {
 835         unsigned int cls, con, tag;
 836         unsigned char *end;
 837
 838         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 839                 return 0;
 840
 841         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
 842                 return 0;
 843
 844         if (!asn1_ulong_decode(ctx, end, &request->id))
 845                 return 0;
 846
 847         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 848                 return 0;
 849
 850         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
 851                 return 0;
 852
 853         if (!asn1_uint_decode(ctx, end, &request->error_status))
 854                 return 0;
 855
 856         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 857                 return 0;
 858
 859         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
 860                 return 0;
 861
 862         if (!asn1_uint_decode(ctx, end, &request->error_index))
 863                 return 0;
 864
 865         return 1;
 866 }
 867
 868 /*
 869  * Fast checksum update for possibly oddly-aligned UDP byte, from the
 870  * code example in the draft.
 871  */
 872 static void fast_csum(__sum16 *csum,
 873                       const unsigned char *optr,
 874                       const unsigned char *nptr,
 875                       int offset)
 876 {
 877         unsigned char s[4];
 878
 879         if (offset & 1) {
 880                 s[0] = s[2] = 0;
 881                 s[1] = ~*optr;
 882                 s[3] = *nptr;
 883         } else {
 884                 s[1] = s[3] = 0;
 885                 s[0] = ~*optr;
 886                 s[2] = *nptr;
 887         }
 888
 889         *csum = csum_fold(csum_partial(s, 4, ~csum_unfold(*csum)));
 890 }
 891
 892 /*
 893  * Mangle IP address.
 894  *      - begin points to the start of the snmp messgae
 895  *      - addr points to the start of the address
 896  */
 897 static inline void mangle_address(unsigned char *begin,
 898                                   unsigned char *addr,
 899                                   const struct oct1_map *map,
 900                                   __sum16 *check)
 901 {
 902         if (map->from == NOCT1(addr)) {
 903                 u_int32_t old;
 904
 905                 if (debug)
 906                         memcpy(&old, addr, sizeof(old));
 907
 908                 *addr = map->to;
 909
 910                 /* Update UDP checksum if being used */
 911                 if (*check) {
 912                         fast_csum(check,
 913                                   &map->from, &map->to, addr - begin);
 914
 915                 }
 916
 917                 if (debug)
 918                         printk(KERN_DEBUG "bsalg: mapped %u.%u.%u.%u to "
 919                                "%u.%u.%u.%u\n", NIPQUAD(old), NIPQUAD(*addr));
 920         }
 921 }
 922
 923 static unsigned char snmp_trap_decode(struct asn1_ctx *ctx,
 924                                       struct snmp_v1_trap *trap,
 925                                       const struct oct1_map *map,
 926                                       __sum16 *check)
 927 {
 928         unsigned int cls, con, tag, len;
 929         unsigned char *end;
 930
 931         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 932                 return 0;
 933
 934         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_OJI)
 935                 return 0;
 936
 937         if (!asn1_oid_decode(ctx, end, &trap->id, &trap->id_len))
 938                 return 0;
 939
 940         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 941                 goto err_id_free;
 942
 943         if (!((cls == ASN1_APL && con == ASN1_PRI && tag == SNMP_IPA) ||
 944               (cls == ASN1_UNI && con == ASN1_PRI && tag == ASN1_OTS)))
 945                 goto err_id_free;
 946
 947         if (!asn1_octets_decode(ctx, end, (unsigned char **)&trap->ip_address, &len))
 948                 goto err_id_free;
 949
 950         /* IPv4 only */
 951         if (len != 4)
 952                 goto err_addr_free;
 953
 954         mangle_address(ctx->begin, ctx->pointer - 4, map, check);
 955
 956         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 957                 goto err_addr_free;
 958
 959         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
 960                 goto err_addr_free;
 961
 962         if (!asn1_uint_decode(ctx, end, &trap->general))
 963                 goto err_addr_free;
 964
 965         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 966                 goto err_addr_free;
 967
 968         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
 969                 goto err_addr_free;
 970
 971         if (!asn1_uint_decode(ctx, end, &trap->specific))
 972                 goto err_addr_free;
 973
 974         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 975                 goto err_addr_free;
 976
 977         if (!((cls == ASN1_APL && con == ASN1_PRI && tag == SNMP_TIT) ||
 978               (cls == ASN1_UNI && con == ASN1_PRI && tag == ASN1_INT)))
 979                 goto err_addr_free;
 980
 981         if (!asn1_ulong_decode(ctx, end, &trap->time))
 982                 goto err_addr_free;
 983
 984         return 1;
 985
 986 err_addr_free:
 987         kfree((unsigned long *)trap->ip_address);
 988
 989 err_id_free:
 990         kfree(trap->id);
 991
 992         return 0;
 993 }
 994
 995 /*****************************************************************************
 996  *
 997  * Misc. routines
 998  *
 999  *****************************************************************************/
1000
1001 static void hex_dump(const unsigned char *buf, size_t len)
1002 {
1003         size_t i;
1004
1005         for (i = 0; i < len; i++) {
1006                 if (i && !(i % 16))
1007                         printk("\n");
1008                 printk("%02x ", *(buf + i));
1009         }
1010         printk("\n");
1011 }
1012
1013 /*
1014  * Parse and mangle SNMP message according to mapping.
1015  * (And this is the fucking 'basic' method).
1016  */
1017 static int snmp_parse_mangle(unsigned char *msg,
1018                              u_int16_t len,
1019                              const struct oct1_map *map,
1020                              __sum16 *check)
1021 {
1022         unsigned char *eoc, *end;
1023         unsigned int cls, con, tag, vers, pdutype;
1024         struct asn1_ctx ctx;
1025         struct asn1_octstr comm;
1026         struct snmp_object **obj;
1027
1028         if (debug > 1)
1029                 hex_dump(msg, len);
1030
1031         asn1_open(&ctx, msg, len);
1032
1033         /*
1034          * Start of SNMP message.
1035          */
1036         if (!asn1_header_decode(&ctx, &eoc, &cls, &con, &tag))
1037                 return 0;
1038         if (cls != ASN1_UNI || con != ASN1_CON || tag != ASN1_SEQ)
1039                 return 0;
1040
1041         /*
1042          * Version 1 or 2 handled.
1043          */
1044         if (!asn1_header_decode(&ctx, &end, &cls, &con, &tag))
1045                 return 0;
1046         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
1047                 return 0;
1048         if (!asn1_uint_decode (&ctx, end, &vers))
1049                 return 0;
1050         if (debug > 1)
1051                 printk(KERN_DEBUG "bsalg: snmp version: %u\n", vers + 1);
1052         if (vers > 1)
1053                 return 1;
1054
1055         /*
1056          * Community.
1057          */
1058         if (!asn1_header_decode (&ctx, &end, &cls, &con, &tag))
1059                 return 0;
1060         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_OTS)
1061                 return 0;
1062         if (!asn1_octets_decode(&ctx, end, &comm.data, &comm.len))
1063                 return 0;
1064         if (debug > 1) {
1065                 unsigned int i;
1066
1067                 printk(KERN_DEBUG "bsalg: community: ");
1068                 for (i = 0; i < comm.len; i++)
1069                         printk("%c", comm.data[i]);
1070                 printk("\n");
1071         }
1072         kfree(comm.data);
1073
1074         /*
1075          * PDU type
1076          */
1077         if (!asn1_header_decode(&ctx, &eoc, &cls, &con, &pdutype))
1078                 return 0;
1079         if (cls != ASN1_CTX || con != ASN1_CON)
1080                 return 0;
1081         if (debug > 1) {
1082                 static const unsigned char *const pdus[] = {
1083                         [SNMP_PDU_GET] = "get",
1084                         [SNMP_PDU_NEXT] = "get-next",
1085                         [SNMP_PDU_RESPONSE] = "response",
1086                         [SNMP_PDU_SET] = "set",
1087                         [SNMP_PDU_TRAP1] = "trapv1",
1088                         [SNMP_PDU_BULK] = "bulk",
1089                         [SNMP_PDU_INFORM] = "inform",
1090                         [SNMP_PDU_TRAP2] = "trapv2"
1091                 };
1092
1093                 if (pdutype > SNMP_PDU_TRAP2)
1094                         printk(KERN_DEBUG "bsalg: bad pdu type %u\n", pdutype);
1095                 else
1096                         printk(KERN_DEBUG "bsalg: pdu: %s\n", pdus[pdutype]);
1097         }
1098         if (pdutype != SNMP_PDU_RESPONSE &&
1099             pdutype != SNMP_PDU_TRAP1 && pdutype != SNMP_PDU_TRAP2)
1100                 return 1;
1101
1102         /*
1103          * Request header or v1 trap
1104          */
1105         if (pdutype == SNMP_PDU_TRAP1) {
1106                 struct snmp_v1_trap trap;
1107                 unsigned char ret = snmp_trap_decode(&ctx, &trap, map, check);
1108
1109                 if (ret) {
1110                         kfree(trap.id);
1111                         kfree((unsigned long *)trap.ip_address);
1112                 } else
1113                         return ret;
1114
1115         } else {
1116                 struct snmp_request req;
1117
1118                 if (!snmp_request_decode(&ctx, &req))
1119                         return 0;
1120
1121                 if (debug > 1)
1122                         printk(KERN_DEBUG "bsalg: request: id=0x%lx error_status=%u "
1123                         "error_index=%u\n", req.id, req.error_status,
1124                         req.error_index);
1125         }
1126
1127         /*
1128          * Loop through objects, look for IP addresses to mangle.
1129          */
1130         if (!asn1_header_decode(&ctx, &eoc, &cls, &con, &tag))
1131                 return 0;
1132
1133         if (cls != ASN1_UNI || con != ASN1_CON || tag != ASN1_SEQ)
1134                 return 0;
1135
1136         obj = kmalloc(sizeof(struct snmp_object), GFP_ATOMIC);
1137         if (obj == NULL) {
1138                 if (net_ratelimit())
1139                         printk(KERN_WARNING "OOM in bsalg(%d)\n", __LINE__);
1140                 return 0;
1141         }
1142
1143         while (!asn1_eoc_decode(&ctx, eoc)) {
1144                 unsigned int i;
1145
1146                 if (!snmp_object_decode(&ctx, obj)) {
1147                         if (*obj) {
1148                                 kfree((*obj)->id);
1149                                 kfree(*obj);
1150                         }
1151                         kfree(obj);
1152                         return 0;
1153                 }
1154
1155                 if (debug > 1) {
1156                         printk(KERN_DEBUG "bsalg: object: ");
1157                         for (i = 0; i < (*obj)->id_len; i++) {
1158                                 if (i > 0)
1159                                         printk(".");
1160                                 printk("%lu", (*obj)->id[i]);
1161                         }
1162                         printk(": type=%u\n", (*obj)->type);
1163
1164                 }
1165
1166                 if ((*obj)->type == SNMP_IPADDR)
1167                         mangle_address(ctx.begin, ctx.pointer - 4 , map, check);
1168
1169                 kfree((*obj)->id);
1170                 kfree(*obj);
1171         }
1172         kfree(obj);
1173
1174         if (!asn1_eoc_decode(&ctx, eoc))
1175                 return 0;
1176
1177         return 1;
1178 }
1179
1180 /*****************************************************************************
1181  *
1182  * NAT routines.
1183  *
1184  *****************************************************************************/
1185
1186 /*
1187  * SNMP translation routine.
1188  */
1189 static int snmp_translate(struct nf_conn *ct,
1190                           enum ip_conntrack_info ctinfo,
1191                           struct sk_buff *skb)
1192 {
1193         struct iphdr *iph = ip_hdr(skb);
1194         struct udphdr *udph = (struct udphdr *)((__be32 *)iph + iph->ihl);
1195         u_int16_t udplen = ntohs(udph->len);
1196         u_int16_t paylen = udplen - sizeof(struct udphdr);
1197         int dir = CTINFO2DIR(ctinfo);
1198         struct oct1_map map;
1199
1200         /*
1201          * Determine mappping for application layer addresses based
1202          * on NAT manipulations for the packet.
1203          */
1204         if (dir == IP_CT_DIR_ORIGINAL) {
1205                 /* SNAT traps */
1206                 map.from = NOCT1(&ct->tuplehash[dir].tuple.src.u3.ip);
1207                 map.to = NOCT1(&ct->tuplehash[!dir].tuple.dst.u3.ip);
1208         } else {
1209                 /* DNAT replies */
1210                 map.from = NOCT1(&ct->tuplehash[dir].tuple.src.u3.ip);
1211                 map.to = NOCT1(&ct->tuplehash[!dir].tuple.dst.u3.ip);
1212         }
1213
1214         if (map.from == map.to)
1215                 return NF_ACCEPT;
1216
1217         if (!snmp_parse_mangle((unsigned char *)udph + sizeof(struct udphdr),
1218                                paylen, &map, &udph->check)) {
1219                 if (net_ratelimit())
1220                         printk(KERN_WARNING "bsalg: parser failed\n");
1221                 return NF_DROP;
1222         }
1223         return NF_ACCEPT;
1224 }
1225
1226 /* We don't actually set up expectations, just adjust internal IP
1227  * addresses if this is being NATted */
1228 static int help(struct sk_buff *skb, unsigned int protoff,
1229                 struct nf_conn *ct,
1230                 enum ip_conntrack_info ctinfo)
1231 {
1232         int dir = CTINFO2DIR(ctinfo);
1233         unsigned int ret;
1234         const struct iphdr *iph = ip_hdr(skb);
1235         const struct udphdr *udph = (struct udphdr *)((__be32 *)iph + iph->ihl);
1236
1237         /* SNMP replies and originating SNMP traps get mangled */
1238         if (udph->source == htons(SNMP_PORT) && dir != IP_CT_DIR_REPLY)
1239                 return NF_ACCEPT;
1240         if (udph->dest == htons(SNMP_TRAP_PORT) && dir != IP_CT_DIR_ORIGINAL)
1241                 return NF_ACCEPT;
1242
1243         /* No NAT? */
1244         if (!(ct->status & IPS_NAT_MASK))
1245                 return NF_ACCEPT;
1246
1247         /*
1248          * Make sure the packet length is ok.  So far, we were only guaranteed
1249          * to have a valid length IP header plus 8 bytes, which means we have
1250          * enough room for a UDP header.  Just verify the UDP length field so we
1251          * can mess around with the payload.
1252          */
1253         if (ntohs(udph->len) != skb->len - (iph->ihl << 2)) {
1254                  if (net_ratelimit())
1255                          printk(KERN_WARNING "SNMP: dropping malformed packet "
1256                                 "src=%u.%u.%u.%u dst=%u.%u.%u.%u\n",
1257                                 NIPQUAD(iph->saddr), NIPQUAD(iph->daddr));
1258                  return NF_DROP;
1259         }
1260
1261         if (!skb_make_writable(skb, skb->len))
1262                 return NF_DROP;
1263
1264         spin_lock_bh(&snmp_lock);
1265         ret = snmp_translate(ct, ctinfo, skb);
1266         spin_unlock_bh(&snmp_lock);
1267         return ret;
1268 }
1269
1270 static const struct nf_conntrack_expect_policy snmp_exp_policy = {
1271         .max_expected   = 0,
1272         .timeout        = 180,
1273 };
1274
1275 static struct nf_conntrack_helper snmp_helper __read_mostly = {
1276         .me                     = THIS_MODULE,
1277         .help                   = help,
1278         .expect_policy          = &snmp_exp_policy,
1279         .name                   = "snmp",
1280         .tuple.src.l3num        = AF_INET,
1281         .tuple.src.u.udp.port   = __constant_htons(SNMP_PORT),
1282         .tuple.dst.protonum     = IPPROTO_UDP,
1283 };
1284
1285 static struct nf_conntrack_helper snmp_trap_helper __read_mostly = {
1286         .me                     = THIS_MODULE,
1287         .help                   = help,
1288         .expect_policy          = &snmp_exp_policy,
1289         .name                   = "snmp_trap",
1290         .tuple.src.l3num        = AF_INET,
1291         .tuple.src.u.udp.port   = __constant_htons(SNMP_TRAP_PORT),
1292         .tuple.dst.protonum     = IPPROTO_UDP,
1293 };
1294
1295 /*****************************************************************************
1296  *
1297  * Module stuff.
1298  *
1299  *****************************************************************************/
1300
1301 static int __init nf_nat_snmp_basic_init(void)
1302 {
1303         int ret = 0;
1304
1305         ret = nf_conntrack_helper_register(&snmp_helper);
1306         if (ret < 0)
1307                 return ret;
1308         ret = nf_conntrack_helper_register(&snmp_trap_helper);
1309         if (ret < 0) {
1310                 nf_conntrack_helper_unregister(&snmp_helper);
1311                 return ret;
1312         }
1313         return ret;
1314 }
1315
1316 static void __exit nf_nat_snmp_basic_fini(void)
1317 {
1318         nf_conntrack_helper_unregister(&snmp_helper);
1319         nf_conntrack_helper_unregister(&snmp_trap_helper);
1320 }
1321
1322 module_init(nf_nat_snmp_basic_init);
1323 module_exit(nf_nat_snmp_basic_fini);
1324
1325 module_param(debug, int, 0600);