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