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_helper.h>
  54 #include <net/netfilter/nf_nat_helper.h>
  55
  56 MODULE_LICENSE("GPL");
  57 MODULE_AUTHOR("James Morris <jmorris@intercode.com.au>");
  58 MODULE_DESCRIPTION("Basic SNMP Application Layer Gateway");
  59 MODULE_ALIAS("ip_nat_snmp_basic");
  60
  61 #define SNMP_PORT 161
  62 #define SNMP_TRAP_PORT 162
  63 #define NOCT1(n) (*(u8 *)n)
  64
  65 static int debug;
  66 static DEFINE_SPINLOCK(snmp_lock);
  67
  68 /*
  69  * Application layer address mapping mimics the NAT mapping, but
  70  * only for the first octet in this case (a more flexible system
  71  * can be implemented if needed).
  72  */
  73 struct oct1_map
  74 {
  75         u_int8_t from;
  76         u_int8_t to;
  77 };
  78
  79
  80 /*****************************************************************************
  81  *
  82  * Basic ASN.1 decoding routines (gxsnmp author Dirk Wisse)
  83  *
  84  *****************************************************************************/
  85
  86 /* Class */
  87 #define ASN1_UNI        0       /* Universal */
  88 #define ASN1_APL        1       /* Application */
  89 #define ASN1_CTX        2       /* Context */
  90 #define ASN1_PRV        3       /* Private */
  91
  92 /* Tag */
  93 #define ASN1_EOC        0       /* End Of Contents */
  94 #define ASN1_BOL        1       /* Boolean */
  95 #define ASN1_INT        2       /* Integer */
  96 #define ASN1_BTS        3       /* Bit String */
  97 #define ASN1_OTS        4       /* Octet String */
  98 #define ASN1_NUL        5       /* Null */
  99 #define ASN1_OJI        6       /* Object Identifier  */
 100 #define ASN1_OJD        7       /* Object Description */
 101 #define ASN1_EXT        8       /* External */
 102 #define ASN1_SEQ        16      /* Sequence */
 103 #define ASN1_SET        17      /* Set */
 104 #define ASN1_NUMSTR     18      /* Numerical String */
 105 #define ASN1_PRNSTR     19      /* Printable String */
 106 #define ASN1_TEXSTR     20      /* Teletext String */
 107 #define ASN1_VIDSTR     21      /* Video String */
 108 #define ASN1_IA5STR     22      /* IA5 String */
 109 #define ASN1_UNITIM     23      /* Universal Time */
 110 #define ASN1_GENTIM     24      /* General Time */
 111 #define ASN1_GRASTR     25      /* Graphical String */
 112 #define ASN1_VISSTR     26      /* Visible String */
 113 #define ASN1_GENSTR     27      /* General String */
 114
 115 /* Primitive / Constructed methods*/
 116 #define ASN1_PRI        0       /* Primitive */
 117 #define ASN1_CON        1       /* Constructed */
 118
 119 /*
 120  * Error codes.
 121  */
 122 #define ASN1_ERR_NOERROR                0
 123 #define ASN1_ERR_DEC_EMPTY              2
 124 #define ASN1_ERR_DEC_EOC_MISMATCH       3
 125 #define ASN1_ERR_DEC_LENGTH_MISMATCH    4
 126 #define ASN1_ERR_DEC_BADVALUE           5
 127
 128 /*
 129  * ASN.1 context.
 130  */
 131 struct asn1_ctx
 132 {
 133         int error;                      /* Error condition */
 134         unsigned char *pointer;         /* Octet just to be decoded */
 135         unsigned char *begin;           /* First octet */
 136         unsigned char *end;             /* Octet after last octet */
 137 };
 138
 139 /*
 140  * Octet string (not null terminated)
 141  */
 142 struct asn1_octstr
 143 {
 144         unsigned char *data;
 145         unsigned int len;
 146 };
 147
 148 static void asn1_open(struct asn1_ctx *ctx,
 149                       unsigned char *buf,
 150                       unsigned int len)
 151 {
 152         ctx->begin = buf;
 153         ctx->end = buf + len;
 154         ctx->pointer = buf;
 155         ctx->error = ASN1_ERR_NOERROR;
 156 }
 157
 158 static unsigned char asn1_octet_decode(struct asn1_ctx *ctx, unsigned char *ch)
 159 {
 160         if (ctx->pointer >= ctx->end) {
 161                 ctx->error = ASN1_ERR_DEC_EMPTY;
 162                 return 0;
 163         }
 164         *ch = *(ctx->pointer)++;
 165         return 1;
 166 }
 167
 168 static unsigned char asn1_tag_decode(struct asn1_ctx *ctx, unsigned int *tag)
 169 {
 170         unsigned char ch;
 171
 172         *tag = 0;
 173
 174         do
 175         {
 176                 if (!asn1_octet_decode(ctx, &ch))
 177                         return 0;
 178                 *tag <<= 7;
 179                 *tag |= ch & 0x7F;
 180         } while ((ch & 0x80) == 0x80);
 181         return 1;
 182 }
 183
 184 static unsigned char asn1_id_decode(struct asn1_ctx *ctx,
 185                                     unsigned int *cls,
 186                                     unsigned int *con,
 187                                     unsigned int *tag)
 188 {
 189         unsigned char ch;
 190
 191         if (!asn1_octet_decode(ctx, &ch))
 192                 return 0;
 193
 194         *cls = (ch & 0xC0) >> 6;
 195         *con = (ch & 0x20) >> 5;
 196         *tag = (ch & 0x1F);
 197
 198         if (*tag == 0x1F) {
 199                 if (!asn1_tag_decode(ctx, tag))
 200                         return 0;
 201         }
 202         return 1;
 203 }
 204
 205 static unsigned char asn1_length_decode(struct asn1_ctx *ctx,
 206                                         unsigned int *def,
 207                                         unsigned int *len)
 208 {
 209         unsigned char ch, cnt;
 210
 211         if (!asn1_octet_decode(ctx, &ch))
 212                 return 0;
 213
 214         if (ch == 0x80)
 215                 *def = 0;
 216         else {
 217                 *def = 1;
 218
 219                 if (ch < 0x80)
 220                         *len = ch;
 221                 else {
 222                         cnt = (unsigned char) (ch & 0x7F);
 223                         *len = 0;
 224
 225                         while (cnt > 0) {
 226                                 if (!asn1_octet_decode(ctx, &ch))
 227                                         return 0;
 228                                 *len <<= 8;
 229                                 *len |= ch;
 230                                 cnt--;
 231                         }
 232                 }
 233         }
 234         return 1;
 235 }
 236
 237 static unsigned char asn1_header_decode(struct asn1_ctx *ctx,
 238                                         unsigned char **eoc,
 239                                         unsigned int *cls,
 240                                         unsigned int *con,
 241                                         unsigned int *tag)
 242 {
 243         unsigned int def, len;
 244
 245         if (!asn1_id_decode(ctx, cls, con, tag))
 246                 return 0;
 247
 248         def = len = 0;
 249         if (!asn1_length_decode(ctx, &def, &len))
 250                 return 0;
 251
 252         if (def)
 253                 *eoc = ctx->pointer + len;
 254         else
 255                 *eoc = NULL;
 256         return 1;
 257 }
 258
 259 static unsigned char asn1_eoc_decode(struct asn1_ctx *ctx, unsigned char *eoc)
 260 {
 261         unsigned char ch;
 262
 263         if (eoc == 0) {
 264                 if (!asn1_octet_decode(ctx, &ch))
 265                         return 0;
 266
 267                 if (ch != 0x00) {
 268                         ctx->error = ASN1_ERR_DEC_EOC_MISMATCH;
 269                         return 0;
 270                 }
 271
 272                 if (!asn1_octet_decode(ctx, &ch))
 273                         return 0;
 274
 275                 if (ch != 0x00) {
 276                         ctx->error = ASN1_ERR_DEC_EOC_MISMATCH;
 277                         return 0;
 278                 }
 279                 return 1;
 280         } else {
 281                 if (ctx->pointer != eoc) {
 282                         ctx->error = ASN1_ERR_DEC_LENGTH_MISMATCH;
 283                         return 0;
 284                 }
 285                 return 1;
 286         }
 287 }
 288
 289 static unsigned char asn1_null_decode(struct asn1_ctx *ctx, unsigned char *eoc)
 290 {
 291         ctx->pointer = eoc;
 292         return 1;
 293 }
 294
 295 static unsigned char asn1_long_decode(struct asn1_ctx *ctx,
 296                                       unsigned char *eoc,
 297                                       long *integer)
 298 {
 299         unsigned char ch;
 300         unsigned int  len;
 301
 302         if (!asn1_octet_decode(ctx, &ch))
 303                 return 0;
 304
 305         *integer = (signed char) ch;
 306         len = 1;
 307
 308         while (ctx->pointer < eoc) {
 309                 if (++len > sizeof (long)) {
 310                         ctx->error = ASN1_ERR_DEC_BADVALUE;
 311                         return 0;
 312                 }
 313
 314                 if (!asn1_octet_decode(ctx, &ch))
 315                         return 0;
 316
 317                 *integer <<= 8;
 318                 *integer |= ch;
 319         }
 320         return 1;
 321 }
 322
 323 static unsigned char asn1_uint_decode(struct asn1_ctx *ctx,
 324                                       unsigned char *eoc,
 325                                       unsigned int *integer)
 326 {
 327         unsigned char ch;
 328         unsigned int  len;
 329
 330         if (!asn1_octet_decode(ctx, &ch))
 331                 return 0;
 332
 333         *integer = ch;
 334         if (ch == 0) len = 0;
 335         else len = 1;
 336
 337         while (ctx->pointer < eoc) {
 338                 if (++len > sizeof (unsigned int)) {
 339                         ctx->error = ASN1_ERR_DEC_BADVALUE;
 340                         return 0;
 341                 }
 342
 343                 if (!asn1_octet_decode(ctx, &ch))
 344                         return 0;
 345
 346                 *integer <<= 8;
 347                 *integer |= ch;
 348         }
 349         return 1;
 350 }
 351
 352 static unsigned char asn1_ulong_decode(struct asn1_ctx *ctx,
 353                                        unsigned char *eoc,
 354                                        unsigned long *integer)
 355 {
 356         unsigned char ch;
 357         unsigned int  len;
 358
 359         if (!asn1_octet_decode(ctx, &ch))
 360                 return 0;
 361
 362         *integer = ch;
 363         if (ch == 0) len = 0;
 364         else len = 1;
 365
 366         while (ctx->pointer < eoc) {
 367                 if (++len > sizeof (unsigned long)) {
 368                         ctx->error = ASN1_ERR_DEC_BADVALUE;
 369                         return 0;
 370                 }
 371
 372                 if (!asn1_octet_decode(ctx, &ch))
 373                         return 0;
 374
 375                 *integer <<= 8;
 376                 *integer |= ch;
 377         }
 378         return 1;
 379 }
 380
 381 static unsigned char asn1_octets_decode(struct asn1_ctx *ctx,
 382                                         unsigned char *eoc,
 383                                         unsigned char **octets,
 384                                         unsigned int *len)
 385 {
 386         unsigned char *ptr;
 387
 388         *len = 0;
 389
 390         *octets = kmalloc(eoc - ctx->pointer, GFP_ATOMIC);
 391         if (*octets == NULL) {
 392                 if (net_ratelimit())
 393                         printk("OOM in bsalg (%d)\n", __LINE__);
 394                 return 0;
 395         }
 396
 397         ptr = *octets;
 398         while (ctx->pointer < eoc) {
 399                 if (!asn1_octet_decode(ctx, (unsigned char *)ptr++)) {
 400                         kfree(*octets);
 401                         *octets = NULL;
 402                         return 0;
 403                 }
 404                 (*len)++;
 405         }
 406         return 1;
 407 }
 408
 409 static unsigned char asn1_subid_decode(struct asn1_ctx *ctx,
 410                                        unsigned long *subid)
 411 {
 412         unsigned char ch;
 413
 414         *subid = 0;
 415
 416         do {
 417                 if (!asn1_octet_decode(ctx, &ch))
 418                         return 0;
 419
 420                 *subid <<= 7;
 421                 *subid |= ch & 0x7F;
 422         } while ((ch & 0x80) == 0x80);
 423         return 1;
 424 }
 425
 426 static unsigned char asn1_oid_decode(struct asn1_ctx *ctx,
 427                                      unsigned char *eoc,
 428                                      unsigned long **oid,
 429                                      unsigned int *len)
 430 {
 431         unsigned long subid;
 432         unsigned int  size;
 433         unsigned long *optr;
 434
 435         size = eoc - ctx->pointer + 1;
 436         *oid = kmalloc(size * sizeof(unsigned long), GFP_ATOMIC);
 437         if (*oid == NULL) {
 438                 if (net_ratelimit())
 439                         printk("OOM in bsalg (%d)\n", __LINE__);
 440                 return 0;
 441         }
 442
 443         optr = *oid;
 444
 445         if (!asn1_subid_decode(ctx, &subid)) {
 446                 kfree(*oid);
 447                 *oid = NULL;
 448                 return 0;
 449         }
 450
 451         if (subid < 40) {
 452                 optr [0] = 0;
 453                 optr [1] = subid;
 454         } else if (subid < 80) {
 455                 optr [0] = 1;
 456                 optr [1] = subid - 40;
 457         } else {
 458                 optr [0] = 2;
 459                 optr [1] = subid - 80;
 460         }
 461
 462         *len = 2;
 463         optr += 2;
 464
 465         while (ctx->pointer < eoc) {
 466                 if (++(*len) > size) {
 467                         ctx->error = ASN1_ERR_DEC_BADVALUE;
 468                         kfree(*oid);
 469                         *oid = NULL;
 470                         return 0;
 471                 }
 472
 473                 if (!asn1_subid_decode(ctx, optr++)) {
 474                         kfree(*oid);
 475                         *oid = NULL;
 476                         return 0;
 477                 }
 478         }
 479         return 1;
 480 }
 481
 482 /*****************************************************************************
 483  *
 484  * SNMP decoding routines (gxsnmp author Dirk Wisse)
 485  *
 486  *****************************************************************************/
 487
 488 /* SNMP Versions */
 489 #define SNMP_V1                         0
 490 #define SNMP_V2C                        1
 491 #define SNMP_V2                         2
 492 #define SNMP_V3                         3
 493
 494 /* Default Sizes */
 495 #define SNMP_SIZE_COMM                  256
 496 #define SNMP_SIZE_OBJECTID              128
 497 #define SNMP_SIZE_BUFCHR                256
 498 #define SNMP_SIZE_BUFINT                128
 499 #define SNMP_SIZE_SMALLOBJECTID         16
 500
 501 /* Requests */
 502 #define SNMP_PDU_GET                    0
 503 #define SNMP_PDU_NEXT                   1
 504 #define SNMP_PDU_RESPONSE               2
 505 #define SNMP_PDU_SET                    3
 506 #define SNMP_PDU_TRAP1                  4
 507 #define SNMP_PDU_BULK                   5
 508 #define SNMP_PDU_INFORM                 6
 509 #define SNMP_PDU_TRAP2                  7
 510
 511 /* Errors */
 512 #define SNMP_NOERROR                    0
 513 #define SNMP_TOOBIG                     1
 514 #define SNMP_NOSUCHNAME                 2
 515 #define SNMP_BADVALUE                   3
 516 #define SNMP_READONLY                   4
 517 #define SNMP_GENERROR                   5
 518 #define SNMP_NOACCESS                   6
 519 #define SNMP_WRONGTYPE                  7
 520 #define SNMP_WRONGLENGTH                8
 521 #define SNMP_WRONGENCODING              9
 522 #define SNMP_WRONGVALUE                 10
 523 #define SNMP_NOCREATION                 11
 524 #define SNMP_INCONSISTENTVALUE          12
 525 #define SNMP_RESOURCEUNAVAILABLE        13
 526 #define SNMP_COMMITFAILED               14
 527 #define SNMP_UNDOFAILED                 15
 528 #define SNMP_AUTHORIZATIONERROR         16
 529 #define SNMP_NOTWRITABLE                17
 530 #define SNMP_INCONSISTENTNAME           18
 531
 532 /* General SNMP V1 Traps */
 533 #define SNMP_TRAP_COLDSTART             0
 534 #define SNMP_TRAP_WARMSTART             1
 535 #define SNMP_TRAP_LINKDOWN              2
 536 #define SNMP_TRAP_LINKUP                3
 537 #define SNMP_TRAP_AUTFAILURE            4
 538 #define SNMP_TRAP_EQPNEIGHBORLOSS       5
 539 #define SNMP_TRAP_ENTSPECIFIC           6
 540
 541 /* SNMPv1 Types */
 542 #define SNMP_NULL                0
 543 #define SNMP_INTEGER             1    /* l  */
 544 #define SNMP_OCTETSTR            2    /* c  */
 545 #define SNMP_DISPLAYSTR          2    /* c  */
 546 #define SNMP_OBJECTID            3    /* ul */
 547 #define SNMP_IPADDR              4    /* uc */
 548 #define SNMP_COUNTER             5    /* ul */
 549 #define SNMP_GAUGE               6    /* ul */
 550 #define SNMP_TIMETICKS           7    /* ul */
 551 #define SNMP_OPAQUE              8    /* c  */
 552
 553 /* Additional SNMPv2 Types */
 554 #define SNMP_UINTEGER            5    /* ul */
 555 #define SNMP_BITSTR              9    /* uc */
 556 #define SNMP_NSAP               10    /* uc */
 557 #define SNMP_COUNTER64          11    /* ul */
 558 #define SNMP_NOSUCHOBJECT       12
 559 #define SNMP_NOSUCHINSTANCE     13
 560 #define SNMP_ENDOFMIBVIEW       14
 561
 562 union snmp_syntax
 563 {
 564         unsigned char uc[0];    /* 8 bit unsigned */
 565         char c[0];              /* 8 bit signed */
 566         unsigned long ul[0];    /* 32 bit unsigned */
 567         long l[0];              /* 32 bit signed */
 568 };
 569
 570 struct snmp_object
 571 {
 572         unsigned long *id;
 573         unsigned int id_len;
 574         unsigned short type;
 575         unsigned int syntax_len;
 576         union snmp_syntax syntax;
 577 };
 578
 579 struct snmp_request
 580 {
 581         unsigned long id;
 582         unsigned int error_status;
 583         unsigned int error_index;
 584 };
 585
 586 struct snmp_v1_trap
 587 {
 588         unsigned long *id;
 589         unsigned int id_len;
 590         unsigned long ip_address;       /* pointer  */
 591         unsigned int general;
 592         unsigned int specific;
 593         unsigned long time;
 594 };
 595
 596 /* SNMP types */
 597 #define SNMP_IPA    0
 598 #define SNMP_CNT    1
 599 #define SNMP_GGE    2
 600 #define SNMP_TIT    3
 601 #define SNMP_OPQ    4
 602 #define SNMP_C64    6
 603
 604 /* SNMP errors */
 605 #define SERR_NSO    0
 606 #define SERR_NSI    1
 607 #define SERR_EOM    2
 608
 609 static inline void mangle_address(unsigned char *begin,
 610                                   unsigned char *addr,
 611                                   const struct oct1_map *map,
 612                                   __sum16 *check);
 613 struct snmp_cnv
 614 {
 615         unsigned int class;
 616         unsigned int tag;
 617         int syntax;
 618 };
 619
 620 static struct snmp_cnv snmp_conv [] =
 621 {
 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         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, (unsigned char *)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(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                 unsigned char *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 **pskb)
1192 {
1193         struct iphdr *iph = ip_hdr(*pskb);
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 **pskb, 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         struct iphdr *iph = ip_hdr(*pskb);
1235         struct udphdr *udph = (struct udphdr *)((u_int32_t *)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) != (*pskb)->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(pskb, (*pskb)->len))
1262                 return NF_DROP;
1263
1264         spin_lock_bh(&snmp_lock);
1265         ret = snmp_translate(ct, ctinfo, pskb);
1266         spin_unlock_bh(&snmp_lock);
1267         return ret;
1268 }
1269
1270 static struct nf_conntrack_helper snmp_helper __read_mostly = {
1271         .max_expected           = 0,
1272         .timeout                = 180,
1273         .me                     = THIS_MODULE,
1274         .help                   = help,
1275         .name                   = "snmp",
1276         .tuple.src.l3num        = AF_INET,
1277         .tuple.src.u.udp.port   = __constant_htons(SNMP_PORT),
1278         .tuple.dst.protonum     = IPPROTO_UDP,
1279         .mask.src.l3num         = 0xFFFF,
1280         .mask.src.u.udp.port    = __constant_htons(0xFFFF),
1281         .mask.dst.protonum      = 0xFF,
1282 };
1283
1284 static struct nf_conntrack_helper snmp_trap_helper __read_mostly = {
1285         .max_expected           = 0,
1286         .timeout                = 180,
1287         .me                     = THIS_MODULE,
1288         .help                   = help,
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         .mask.src.l3num         = 0xFFFF,
1294         .mask.src.u.udp.port    = __constant_htons(0xFFFF),
1295         .mask.dst.protonum      = 0xFF,
1296 };
1297
1298 /*****************************************************************************
1299  *
1300  * Module stuff.
1301  *
1302  *****************************************************************************/
1303
1304 static int __init nf_nat_snmp_basic_init(void)
1305 {
1306         int ret = 0;
1307
1308         ret = nf_conntrack_helper_register(&snmp_helper);
1309         if (ret < 0)
1310                 return ret;
1311         ret = nf_conntrack_helper_register(&snmp_trap_helper);
1312         if (ret < 0) {
1313                 nf_conntrack_helper_unregister(&snmp_helper);
1314                 return ret;
1315         }
1316         return ret;
1317 }
1318
1319 static void __exit nf_nat_snmp_basic_fini(void)
1320 {
1321         nf_conntrack_helper_unregister(&snmp_helper);
1322         nf_conntrack_helper_unregister(&snmp_trap_helper);
1323 }
1324
1325 module_init(nf_nat_snmp_basic_init);
1326 module_exit(nf_nat_snmp_basic_fini);
1327
1328 module_param(debug, int, 0600);