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  * Copyright (c) 2006-2010 Patrick McHardy <kaber@trash.net>
  43  */
  44 #include <linux/module.h>
  45 #include <linux/moduleparam.h>
  46 #include <linux/types.h>
  47 #include <linux/kernel.h>
  48 #include <linux/slab.h>
  49 #include <linux/in.h>
  50 #include <linux/ip.h>
  51 #include <linux/udp.h>
  52 #include <net/checksum.h>
  53 #include <net/udp.h>
  54
  55 #include <net/netfilter/nf_nat.h>
  56 #include <net/netfilter/nf_conntrack_expect.h>
  57 #include <net/netfilter/nf_conntrack_helper.h>
  58 #include <net/netfilter/nf_nat_helper.h>
  59 #include <linux/netfilter/nf_conntrack_snmp.h>
  60
  61 MODULE_LICENSE("GPL");
  62 MODULE_AUTHOR("James Morris <jmorris@intercode.com.au>");
  63 MODULE_DESCRIPTION("Basic SNMP Application Layer Gateway");
  64 MODULE_ALIAS("ip_nat_snmp_basic");
  65
  66 #define SNMP_PORT 161
  67 #define SNMP_TRAP_PORT 162
  68 #define NOCT1(n) (*(u8 *)(n))
  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 = 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
 240         /* don't trust len bigger than ctx buffer */
 241         if (*len > ctx->end - ctx->pointer)
 242                 return 0;
 243
 244         return 1;
 245 }
 246
 247 static unsigned char asn1_header_decode(struct asn1_ctx *ctx,
 248                                         unsigned char **eoc,
 249                                         unsigned int *cls,
 250                                         unsigned int *con,
 251                                         unsigned int *tag)
 252 {
 253         unsigned int def, len;
 254
 255         if (!asn1_id_decode(ctx, cls, con, tag))
 256                 return 0;
 257
 258         def = len = 0;
 259         if (!asn1_length_decode(ctx, &def, &len))
 260                 return 0;
 261
 262         /* primitive shall be definite, indefinite shall be constructed */
 263         if (*con == ASN1_PRI && !def)
 264                 return 0;
 265
 266         if (def)
 267                 *eoc = ctx->pointer + len;
 268         else
 269                 *eoc = NULL;
 270         return 1;
 271 }
 272
 273 static unsigned char asn1_eoc_decode(struct asn1_ctx *ctx, unsigned char *eoc)
 274 {
 275         unsigned char ch;
 276
 277         if (eoc == NULL) {
 278                 if (!asn1_octet_decode(ctx, &ch))
 279                         return 0;
 280
 281                 if (ch != 0x00) {
 282                         ctx->error = ASN1_ERR_DEC_EOC_MISMATCH;
 283                         return 0;
 284                 }
 285
 286                 if (!asn1_octet_decode(ctx, &ch))
 287                         return 0;
 288
 289                 if (ch != 0x00) {
 290                         ctx->error = ASN1_ERR_DEC_EOC_MISMATCH;
 291                         return 0;
 292                 }
 293                 return 1;
 294         } else {
 295                 if (ctx->pointer != eoc) {
 296                         ctx->error = ASN1_ERR_DEC_LENGTH_MISMATCH;
 297                         return 0;
 298                 }
 299                 return 1;
 300         }
 301 }
 302
 303 static unsigned char asn1_null_decode(struct asn1_ctx *ctx, unsigned char *eoc)
 304 {
 305         ctx->pointer = eoc;
 306         return 1;
 307 }
 308
 309 static unsigned char asn1_long_decode(struct asn1_ctx *ctx,
 310                                       unsigned char *eoc,
 311                                       long *integer)
 312 {
 313         unsigned char ch;
 314         unsigned int  len;
 315
 316         if (!asn1_octet_decode(ctx, &ch))
 317                 return 0;
 318
 319         *integer = (signed char) ch;
 320         len = 1;
 321
 322         while (ctx->pointer < eoc) {
 323                 if (++len > sizeof (long)) {
 324                         ctx->error = ASN1_ERR_DEC_BADVALUE;
 325                         return 0;
 326                 }
 327
 328                 if (!asn1_octet_decode(ctx, &ch))
 329                         return 0;
 330
 331                 *integer <<= 8;
 332                 *integer |= ch;
 333         }
 334         return 1;
 335 }
 336
 337 static unsigned char asn1_uint_decode(struct asn1_ctx *ctx,
 338                                       unsigned char *eoc,
 339                                       unsigned int *integer)
 340 {
 341         unsigned char ch;
 342         unsigned int  len;
 343
 344         if (!asn1_octet_decode(ctx, &ch))
 345                 return 0;
 346
 347         *integer = ch;
 348         if (ch == 0) len = 0;
 349         else len = 1;
 350
 351         while (ctx->pointer < eoc) {
 352                 if (++len > sizeof (unsigned int)) {
 353                         ctx->error = ASN1_ERR_DEC_BADVALUE;
 354                         return 0;
 355                 }
 356
 357                 if (!asn1_octet_decode(ctx, &ch))
 358                         return 0;
 359
 360                 *integer <<= 8;
 361                 *integer |= ch;
 362         }
 363         return 1;
 364 }
 365
 366 static unsigned char asn1_ulong_decode(struct asn1_ctx *ctx,
 367                                        unsigned char *eoc,
 368                                        unsigned long *integer)
 369 {
 370         unsigned char ch;
 371         unsigned int  len;
 372
 373         if (!asn1_octet_decode(ctx, &ch))
 374                 return 0;
 375
 376         *integer = ch;
 377         if (ch == 0) len = 0;
 378         else len = 1;
 379
 380         while (ctx->pointer < eoc) {
 381                 if (++len > sizeof (unsigned long)) {
 382                         ctx->error = ASN1_ERR_DEC_BADVALUE;
 383                         return 0;
 384                 }
 385
 386                 if (!asn1_octet_decode(ctx, &ch))
 387                         return 0;
 388
 389                 *integer <<= 8;
 390                 *integer |= ch;
 391         }
 392         return 1;
 393 }
 394
 395 static unsigned char asn1_octets_decode(struct asn1_ctx *ctx,
 396                                         unsigned char *eoc,
 397                                         unsigned char **octets,
 398                                         unsigned int *len)
 399 {
 400         unsigned char *ptr;
 401
 402         *len = 0;
 403
 404         *octets = kmalloc(eoc - ctx->pointer, GFP_ATOMIC);
 405         if (*octets == NULL)
 406                 return 0;
 407
 408         ptr = *octets;
 409         while (ctx->pointer < eoc) {
 410                 if (!asn1_octet_decode(ctx, ptr++)) {
 411                         kfree(*octets);
 412                         *octets = NULL;
 413                         return 0;
 414                 }
 415                 (*len)++;
 416         }
 417         return 1;
 418 }
 419
 420 static unsigned char asn1_subid_decode(struct asn1_ctx *ctx,
 421                                        unsigned long *subid)
 422 {
 423         unsigned char ch;
 424
 425         *subid = 0;
 426
 427         do {
 428                 if (!asn1_octet_decode(ctx, &ch))
 429                         return 0;
 430
 431                 *subid <<= 7;
 432                 *subid |= ch & 0x7F;
 433         } while ((ch & 0x80) == 0x80);
 434         return 1;
 435 }
 436
 437 static unsigned char asn1_oid_decode(struct asn1_ctx *ctx,
 438                                      unsigned char *eoc,
 439                                      unsigned long **oid,
 440                                      unsigned int *len)
 441 {
 442         unsigned long subid;
 443         unsigned long *optr;
 444         size_t size;
 445
 446         size = eoc - ctx->pointer + 1;
 447
 448         /* first subid actually encodes first two subids */
 449         if (size < 2 || size > ULONG_MAX/sizeof(unsigned long))
 450                 return 0;
 451
 452         *oid = kmalloc(size * sizeof(unsigned long), GFP_ATOMIC);
 453         if (*oid == NULL)
 454                 return 0;
 455
 456         optr = *oid;
 457
 458         if (!asn1_subid_decode(ctx, &subid)) {
 459                 kfree(*oid);
 460                 *oid = NULL;
 461                 return 0;
 462         }
 463
 464         if (subid < 40) {
 465                 optr [0] = 0;
 466                 optr [1] = subid;
 467         } else if (subid < 80) {
 468                 optr [0] = 1;
 469                 optr [1] = subid - 40;
 470         } else {
 471                 optr [0] = 2;
 472                 optr [1] = subid - 80;
 473         }
 474
 475         *len = 2;
 476         optr += 2;
 477
 478         while (ctx->pointer < eoc) {
 479                 if (++(*len) > size) {
 480                         ctx->error = ASN1_ERR_DEC_BADVALUE;
 481                         kfree(*oid);
 482                         *oid = NULL;
 483                         return 0;
 484                 }
 485
 486                 if (!asn1_subid_decode(ctx, optr++)) {
 487                         kfree(*oid);
 488                         *oid = NULL;
 489                         return 0;
 490                 }
 491         }
 492         return 1;
 493 }
 494
 495 /*****************************************************************************
 496  *
 497  * SNMP decoding routines (gxsnmp author Dirk Wisse)
 498  *
 499  *****************************************************************************/
 500
 501 /* SNMP Versions */
 502 #define SNMP_V1                         0
 503 #define SNMP_V2C                        1
 504 #define SNMP_V2                         2
 505 #define SNMP_V3                         3
 506
 507 /* Default Sizes */
 508 #define SNMP_SIZE_COMM                  256
 509 #define SNMP_SIZE_OBJECTID              128
 510 #define SNMP_SIZE_BUFCHR                256
 511 #define SNMP_SIZE_BUFINT                128
 512 #define SNMP_SIZE_SMALLOBJECTID         16
 513
 514 /* Requests */
 515 #define SNMP_PDU_GET                    0
 516 #define SNMP_PDU_NEXT                   1
 517 #define SNMP_PDU_RESPONSE               2
 518 #define SNMP_PDU_SET                    3
 519 #define SNMP_PDU_TRAP1                  4
 520 #define SNMP_PDU_BULK                   5
 521 #define SNMP_PDU_INFORM                 6
 522 #define SNMP_PDU_TRAP2                  7
 523
 524 /* Errors */
 525 #define SNMP_NOERROR                    0
 526 #define SNMP_TOOBIG                     1
 527 #define SNMP_NOSUCHNAME                 2
 528 #define SNMP_BADVALUE                   3
 529 #define SNMP_READONLY                   4
 530 #define SNMP_GENERROR                   5
 531 #define SNMP_NOACCESS                   6
 532 #define SNMP_WRONGTYPE                  7
 533 #define SNMP_WRONGLENGTH                8
 534 #define SNMP_WRONGENCODING              9
 535 #define SNMP_WRONGVALUE                 10
 536 #define SNMP_NOCREATION                 11
 537 #define SNMP_INCONSISTENTVALUE          12
 538 #define SNMP_RESOURCEUNAVAILABLE        13
 539 #define SNMP_COMMITFAILED               14
 540 #define SNMP_UNDOFAILED                 15
 541 #define SNMP_AUTHORIZATIONERROR         16
 542 #define SNMP_NOTWRITABLE                17
 543 #define SNMP_INCONSISTENTNAME           18
 544
 545 /* General SNMP V1 Traps */
 546 #define SNMP_TRAP_COLDSTART             0
 547 #define SNMP_TRAP_WARMSTART             1
 548 #define SNMP_TRAP_LINKDOWN              2
 549 #define SNMP_TRAP_LINKUP                3
 550 #define SNMP_TRAP_AUTFAILURE            4
 551 #define SNMP_TRAP_EQPNEIGHBORLOSS       5
 552 #define SNMP_TRAP_ENTSPECIFIC           6
 553
 554 /* SNMPv1 Types */
 555 #define SNMP_NULL                0
 556 #define SNMP_INTEGER             1    /* l  */
 557 #define SNMP_OCTETSTR            2    /* c  */
 558 #define SNMP_DISPLAYSTR          2    /* c  */
 559 #define SNMP_OBJECTID            3    /* ul */
 560 #define SNMP_IPADDR              4    /* uc */
 561 #define SNMP_COUNTER             5    /* ul */
 562 #define SNMP_GAUGE               6    /* ul */
 563 #define SNMP_TIMETICKS           7    /* ul */
 564 #define SNMP_OPAQUE              8    /* c  */
 565
 566 /* Additional SNMPv2 Types */
 567 #define SNMP_UINTEGER            5    /* ul */
 568 #define SNMP_BITSTR              9    /* uc */
 569 #define SNMP_NSAP               10    /* uc */
 570 #define SNMP_COUNTER64          11    /* ul */
 571 #define SNMP_NOSUCHOBJECT       12
 572 #define SNMP_NOSUCHINSTANCE     13
 573 #define SNMP_ENDOFMIBVIEW       14
 574
 575 union snmp_syntax
 576 {
 577         unsigned char uc[0];    /* 8 bit unsigned */
 578         char c[0];              /* 8 bit signed */
 579         unsigned long ul[0];    /* 32 bit unsigned */
 580         long l[0];              /* 32 bit signed */
 581 };
 582
 583 struct snmp_object
 584 {
 585         unsigned long *id;
 586         unsigned int id_len;
 587         unsigned short type;
 588         unsigned int syntax_len;
 589         union snmp_syntax syntax;
 590 };
 591
 592 struct snmp_request
 593 {
 594         unsigned long id;
 595         unsigned int error_status;
 596         unsigned int error_index;
 597 };
 598
 599 struct snmp_v1_trap
 600 {
 601         unsigned long *id;
 602         unsigned int id_len;
 603         unsigned long ip_address;       /* pointer  */
 604         unsigned int general;
 605         unsigned int specific;
 606         unsigned long time;
 607 };
 608
 609 /* SNMP types */
 610 #define SNMP_IPA    0
 611 #define SNMP_CNT    1
 612 #define SNMP_GGE    2
 613 #define SNMP_TIT    3
 614 #define SNMP_OPQ    4
 615 #define SNMP_C64    6
 616
 617 /* SNMP errors */
 618 #define SERR_NSO    0
 619 #define SERR_NSI    1
 620 #define SERR_EOM    2
 621
 622 static inline void mangle_address(unsigned char *begin,
 623                                   unsigned char *addr,
 624                                   const struct oct1_map *map,
 625                                   __sum16 *check);
 626 struct snmp_cnv
 627 {
 628         unsigned int class;
 629         unsigned int tag;
 630         int syntax;
 631 };
 632
 633 static const struct snmp_cnv snmp_conv[] = {
 634         {ASN1_UNI, ASN1_NUL, SNMP_NULL},
 635         {ASN1_UNI, ASN1_INT, SNMP_INTEGER},
 636         {ASN1_UNI, ASN1_OTS, SNMP_OCTETSTR},
 637         {ASN1_UNI, ASN1_OTS, SNMP_DISPLAYSTR},
 638         {ASN1_UNI, ASN1_OJI, SNMP_OBJECTID},
 639         {ASN1_APL, SNMP_IPA, SNMP_IPADDR},
 640         {ASN1_APL, SNMP_CNT, SNMP_COUNTER},     /* Counter32 */
 641         {ASN1_APL, SNMP_GGE, SNMP_GAUGE},       /* Gauge32 == Unsigned32  */
 642         {ASN1_APL, SNMP_TIT, SNMP_TIMETICKS},
 643         {ASN1_APL, SNMP_OPQ, SNMP_OPAQUE},
 644
 645         /* SNMPv2 data types and errors */
 646         {ASN1_UNI, ASN1_BTS, SNMP_BITSTR},
 647         {ASN1_APL, SNMP_C64, SNMP_COUNTER64},
 648         {ASN1_CTX, SERR_NSO, SNMP_NOSUCHOBJECT},
 649         {ASN1_CTX, SERR_NSI, SNMP_NOSUCHINSTANCE},
 650         {ASN1_CTX, SERR_EOM, SNMP_ENDOFMIBVIEW},
 651         {0,       0,       -1}
 652 };
 653
 654 static unsigned char snmp_tag_cls2syntax(unsigned int tag,
 655                                          unsigned int cls,
 656                                          unsigned short *syntax)
 657 {
 658         const struct snmp_cnv *cnv;
 659
 660         cnv = snmp_conv;
 661
 662         while (cnv->syntax != -1) {
 663                 if (cnv->tag == tag && cnv->class == cls) {
 664                         *syntax = cnv->syntax;
 665                         return 1;
 666                 }
 667                 cnv++;
 668         }
 669         return 0;
 670 }
 671
 672 static unsigned char snmp_object_decode(struct asn1_ctx *ctx,
 673                                         struct snmp_object **obj)
 674 {
 675         unsigned int cls, con, tag, len, idlen;
 676         unsigned short type;
 677         unsigned char *eoc, *end, *p;
 678         unsigned long *lp, *id;
 679         unsigned long ul;
 680         long l;
 681
 682         *obj = NULL;
 683         id = NULL;
 684
 685         if (!asn1_header_decode(ctx, &eoc, &cls, &con, &tag))
 686                 return 0;
 687
 688         if (cls != ASN1_UNI || con != ASN1_CON || tag != ASN1_SEQ)
 689                 return 0;
 690
 691         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 692                 return 0;
 693
 694         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_OJI)
 695                 return 0;
 696
 697         if (!asn1_oid_decode(ctx, end, &id, &idlen))
 698                 return 0;
 699
 700         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag)) {
 701                 kfree(id);
 702                 return 0;
 703         }
 704
 705         if (con != ASN1_PRI) {
 706                 kfree(id);
 707                 return 0;
 708         }
 709
 710         type = 0;
 711         if (!snmp_tag_cls2syntax(tag, cls, &type)) {
 712                 kfree(id);
 713                 return 0;
 714         }
 715
 716         l = 0;
 717         switch (type) {
 718         case SNMP_INTEGER:
 719                 len = sizeof(long);
 720                 if (!asn1_long_decode(ctx, end, &l)) {
 721                         kfree(id);
 722                         return 0;
 723                 }
 724                 *obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
 725                 if (*obj == NULL) {
 726                         kfree(id);
 727                         return 0;
 728                 }
 729                 (*obj)->syntax.l[0] = l;
 730                 break;
 731         case SNMP_OCTETSTR:
 732         case SNMP_OPAQUE:
 733                 if (!asn1_octets_decode(ctx, end, &p, &len)) {
 734                         kfree(id);
 735                         return 0;
 736                 }
 737                 *obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
 738                 if (*obj == NULL) {
 739                         kfree(p);
 740                         kfree(id);
 741                         return 0;
 742                 }
 743                 memcpy((*obj)->syntax.c, p, len);
 744                 kfree(p);
 745                 break;
 746         case SNMP_NULL:
 747         case SNMP_NOSUCHOBJECT:
 748         case SNMP_NOSUCHINSTANCE:
 749         case SNMP_ENDOFMIBVIEW:
 750                 len = 0;
 751                 *obj = kmalloc(sizeof(struct snmp_object), GFP_ATOMIC);
 752                 if (*obj == NULL) {
 753                         kfree(id);
 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, &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                         return 0;
 774                 }
 775                 memcpy((*obj)->syntax.ul, lp, len);
 776                 kfree(lp);
 777                 break;
 778         case SNMP_IPADDR:
 779                 if (!asn1_octets_decode(ctx, end, &p, &len)) {
 780                         kfree(id);
 781                         return 0;
 782                 }
 783                 if (len != 4) {
 784                         kfree(p);
 785                         kfree(id);
 786                         return 0;
 787                 }
 788                 *obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
 789                 if (*obj == NULL) {
 790                         kfree(p);
 791                         kfree(id);
 792                         return 0;
 793                 }
 794                 memcpy((*obj)->syntax.uc, p, len);
 795                 kfree(p);
 796                 break;
 797         case SNMP_COUNTER:
 798         case SNMP_GAUGE:
 799         case SNMP_TIMETICKS:
 800                 len = sizeof(unsigned long);
 801                 if (!asn1_ulong_decode(ctx, end, &ul)) {
 802                         kfree(id);
 803                         return 0;
 804                 }
 805                 *obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
 806                 if (*obj == NULL) {
 807                         kfree(id);
 808                         return 0;
 809                 }
 810                 (*obj)->syntax.ul[0] = ul;
 811                 break;
 812         default:
 813                 kfree(id);
 814                 return 0;
 815         }
 816
 817         (*obj)->syntax_len = len;
 818         (*obj)->type = type;
 819         (*obj)->id = id;
 820         (*obj)->id_len = idlen;
 821
 822         if (!asn1_eoc_decode(ctx, eoc)) {
 823                 kfree(id);
 824                 kfree(*obj);
 825                 *obj = NULL;
 826                 return 0;
 827         }
 828         return 1;
 829 }
 830
 831 static unsigned char snmp_request_decode(struct asn1_ctx *ctx,
 832                                          struct snmp_request *request)
 833 {
 834         unsigned int cls, con, tag;
 835         unsigned char *end;
 836
 837         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 838                 return 0;
 839
 840         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
 841                 return 0;
 842
 843         if (!asn1_ulong_decode(ctx, end, &request->id))
 844                 return 0;
 845
 846         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 847                 return 0;
 848
 849         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
 850                 return 0;
 851
 852         if (!asn1_uint_decode(ctx, end, &request->error_status))
 853                 return 0;
 854
 855         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 856                 return 0;
 857
 858         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
 859                 return 0;
 860
 861         if (!asn1_uint_decode(ctx, end, &request->error_index))
 862                 return 0;
 863
 864         return 1;
 865 }
 866
 867 /*
 868  * Fast checksum update for possibly oddly-aligned UDP byte, from the
 869  * code example in the draft.
 870  */
 871 static void fast_csum(__sum16 *csum,
 872                       const unsigned char *optr,
 873                       const unsigned char *nptr,
 874                       int offset)
 875 {
 876         unsigned char s[4];
 877
 878         if (offset & 1) {
 879                 s[0] = ~0;
 880                 s[1] = ~*optr;
 881                 s[2] = 0;
 882                 s[3] = *nptr;
 883         } else {
 884                 s[0] = ~*optr;
 885                 s[1] = ~0;
 886                 s[2] = *nptr;
 887                 s[3] = 0;
 888         }
 889
 890         *csum = csum_fold(csum_partial(s, 4, ~csum_unfold(*csum)));
 891 }
 892
 893 /*
 894  * Mangle IP address.
 895  *      - begin points to the start of the snmp messgae
 896  *      - addr points to the start of the address
 897  */
 898 static inline void mangle_address(unsigned char *begin,
 899                                   unsigned char *addr,
 900                                   const struct oct1_map *map,
 901                                   __sum16 *check)
 902 {
 903         if (map->from == NOCT1(addr)) {
 904                 u_int32_t old;
 905
 906                 if (debug)
 907                         memcpy(&old, addr, sizeof(old));
 908
 909                 *addr = map->to;
 910
 911                 /* Update UDP checksum if being used */
 912                 if (*check) {
 913                         fast_csum(check,
 914                                   &map->from, &map->to, addr - begin);
 915
 916                 }
 917
 918                 if (debug)
 919                         printk(KERN_DEBUG "bsalg: mapped %pI4 to %pI4\n",
 920                                &old, addr);
 921         }
 922 }
 923
 924 static unsigned char snmp_trap_decode(struct asn1_ctx *ctx,
 925                                       struct snmp_v1_trap *trap,
 926                                       const struct oct1_map *map,
 927                                       __sum16 *check)
 928 {
 929         unsigned int cls, con, tag, len;
 930         unsigned char *end;
 931
 932         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 933                 return 0;
 934
 935         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_OJI)
 936                 return 0;
 937
 938         if (!asn1_oid_decode(ctx, end, &trap->id, &trap->id_len))
 939                 return 0;
 940
 941         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 942                 goto err_id_free;
 943
 944         if (!((cls == ASN1_APL && con == ASN1_PRI && tag == SNMP_IPA) ||
 945               (cls == ASN1_UNI && con == ASN1_PRI && tag == ASN1_OTS)))
 946                 goto err_id_free;
 947
 948         if (!asn1_octets_decode(ctx, end, (unsigned char **)&trap->ip_address, &len))
 949                 goto err_id_free;
 950
 951         /* IPv4 only */
 952         if (len != 4)
 953                 goto err_addr_free;
 954
 955         mangle_address(ctx->begin, ctx->pointer - 4, map, check);
 956
 957         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 958                 goto err_addr_free;
 959
 960         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
 961                 goto err_addr_free;
 962
 963         if (!asn1_uint_decode(ctx, end, &trap->general))
 964                 goto err_addr_free;
 965
 966         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 967                 goto err_addr_free;
 968
 969         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
 970                 goto err_addr_free;
 971
 972         if (!asn1_uint_decode(ctx, end, &trap->specific))
 973                 goto err_addr_free;
 974
 975         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 976                 goto err_addr_free;
 977
 978         if (!((cls == ASN1_APL && con == ASN1_PRI && tag == SNMP_TIT) ||
 979               (cls == ASN1_UNI && con == ASN1_PRI && tag == ASN1_INT)))
 980                 goto err_addr_free;
 981
 982         if (!asn1_ulong_decode(ctx, end, &trap->time))
 983                 goto err_addr_free;
 984
 985         return 1;
 986
 987 err_addr_free:
 988         kfree((unsigned long *)trap->ip_address);
 989
 990 err_id_free:
 991         kfree(trap->id);
 992
 993         return 0;
 994 }
 995
 996 /*****************************************************************************
 997  *
 998  * Misc. routines
 999  *
1000  *****************************************************************************/
1001
1002 static void hex_dump(const unsigned char *buf, size_t len)
1003 {
1004         size_t i;
1005
1006         for (i = 0; i < len; i++) {
1007                 if (i && !(i % 16))
1008                         printk("\n");
1009                 printk("%02x ", *(buf + i));
1010         }
1011         printk("\n");
1012 }
1013
1014 /*
1015  * Parse and mangle SNMP message according to mapping.
1016  * (And this is the fucking 'basic' method).
1017  */
1018 static int snmp_parse_mangle(unsigned char *msg,
1019                              u_int16_t len,
1020                              const struct oct1_map *map,
1021                              __sum16 *check)
1022 {
1023         unsigned char *eoc, *end;
1024         unsigned int cls, con, tag, vers, pdutype;
1025         struct asn1_ctx ctx;
1026         struct asn1_octstr comm;
1027         struct snmp_object *obj;
1028
1029         if (debug > 1)
1030                 hex_dump(msg, len);
1031
1032         asn1_open(&ctx, msg, len);
1033
1034         /*
1035          * Start of SNMP message.
1036          */
1037         if (!asn1_header_decode(&ctx, &eoc, &cls, &con, &tag))
1038                 return 0;
1039         if (cls != ASN1_UNI || con != ASN1_CON || tag != ASN1_SEQ)
1040                 return 0;
1041
1042         /*
1043          * Version 1 or 2 handled.
1044          */
1045         if (!asn1_header_decode(&ctx, &end, &cls, &con, &tag))
1046                 return 0;
1047         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
1048                 return 0;
1049         if (!asn1_uint_decode (&ctx, end, &vers))
1050                 return 0;
1051         if (debug > 1)
1052                 printk(KERN_DEBUG "bsalg: snmp version: %u\n", vers + 1);
1053         if (vers > 1)
1054                 return 1;
1055
1056         /*
1057          * Community.
1058          */
1059         if (!asn1_header_decode (&ctx, &end, &cls, &con, &tag))
1060                 return 0;
1061         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_OTS)
1062                 return 0;
1063         if (!asn1_octets_decode(&ctx, end, &comm.data, &comm.len))
1064                 return 0;
1065         if (debug > 1) {
1066                 unsigned int i;
1067
1068                 printk(KERN_DEBUG "bsalg: community: ");
1069                 for (i = 0; i < comm.len; i++)
1070                         printk("%c", comm.data[i]);
1071                 printk("\n");
1072         }
1073         kfree(comm.data);
1074
1075         /*
1076          * PDU type
1077          */
1078         if (!asn1_header_decode(&ctx, &eoc, &cls, &con, &pdutype))
1079                 return 0;
1080         if (cls != ASN1_CTX || con != ASN1_CON)
1081                 return 0;
1082         if (debug > 1) {
1083                 static const unsigned char *const pdus[] = {
1084                         [SNMP_PDU_GET] = "get",
1085                         [SNMP_PDU_NEXT] = "get-next",
1086                         [SNMP_PDU_RESPONSE] = "response",
1087                         [SNMP_PDU_SET] = "set",
1088                         [SNMP_PDU_TRAP1] = "trapv1",
1089                         [SNMP_PDU_BULK] = "bulk",
1090                         [SNMP_PDU_INFORM] = "inform",
1091                         [SNMP_PDU_TRAP2] = "trapv2"
1092                 };
1093
1094                 if (pdutype > SNMP_PDU_TRAP2)
1095                         printk(KERN_DEBUG "bsalg: bad pdu type %u\n", pdutype);
1096                 else
1097                         printk(KERN_DEBUG "bsalg: pdu: %s\n", pdus[pdutype]);
1098         }
1099         if (pdutype != SNMP_PDU_RESPONSE &&
1100             pdutype != SNMP_PDU_TRAP1 && pdutype != SNMP_PDU_TRAP2)
1101                 return 1;
1102
1103         /*
1104          * Request header or v1 trap
1105          */
1106         if (pdutype == SNMP_PDU_TRAP1) {
1107                 struct snmp_v1_trap trap;
1108                 unsigned char ret = snmp_trap_decode(&ctx, &trap, map, check);
1109
1110                 if (ret) {
1111                         kfree(trap.id);
1112                         kfree((unsigned long *)trap.ip_address);
1113                 } else
1114                         return ret;
1115
1116         } else {
1117                 struct snmp_request req;
1118
1119                 if (!snmp_request_decode(&ctx, &req))
1120                         return 0;
1121
1122                 if (debug > 1)
1123                         printk(KERN_DEBUG "bsalg: request: id=0x%lx error_status=%u "
1124                         "error_index=%u\n", req.id, req.error_status,
1125                         req.error_index);
1126         }
1127
1128         /*
1129          * Loop through objects, look for IP addresses to mangle.
1130          */
1131         if (!asn1_header_decode(&ctx, &eoc, &cls, &con, &tag))
1132                 return 0;
1133
1134         if (cls != ASN1_UNI || con != ASN1_CON || tag != ASN1_SEQ)
1135                 return 0;
1136
1137         while (!asn1_eoc_decode(&ctx, eoc)) {
1138                 unsigned int i;
1139
1140                 if (!snmp_object_decode(&ctx, &obj)) {
1141                         if (obj) {
1142                                 kfree(obj->id);
1143                                 kfree(obj);
1144                         }
1145                         return 0;
1146                 }
1147
1148                 if (debug > 1) {
1149                         printk(KERN_DEBUG "bsalg: object: ");
1150                         for (i = 0; i < obj->id_len; i++) {
1151                                 if (i > 0)
1152                                         printk(".");
1153                                 printk("%lu", obj->id[i]);
1154                         }
1155                         printk(": type=%u\n", obj->type);
1156
1157                 }
1158
1159                 if (obj->type == SNMP_IPADDR)
1160                         mangle_address(ctx.begin, ctx.pointer - 4 , map, check);
1161
1162                 kfree(obj->id);
1163                 kfree(obj);
1164         }
1165
1166         if (!asn1_eoc_decode(&ctx, eoc))
1167                 return 0;
1168
1169         return 1;
1170 }
1171
1172 /*****************************************************************************
1173  *
1174  * NAT routines.
1175  *
1176  *****************************************************************************/
1177
1178 /*
1179  * SNMP translation routine.
1180  */
1181 static int snmp_translate(struct nf_conn *ct,
1182                           enum ip_conntrack_info ctinfo,
1183                           struct sk_buff *skb)
1184 {
1185         struct iphdr *iph = ip_hdr(skb);
1186         struct udphdr *udph = (struct udphdr *)((__be32 *)iph + iph->ihl);
1187         u_int16_t udplen = ntohs(udph->len);
1188         u_int16_t paylen = udplen - sizeof(struct udphdr);
1189         int dir = CTINFO2DIR(ctinfo);
1190         struct oct1_map map;
1191
1192         /*
1193          * Determine mappping for application layer addresses based
1194          * on NAT manipulations for the packet.
1195          */
1196         if (dir == IP_CT_DIR_ORIGINAL) {
1197                 /* SNAT traps */
1198                 map.from = NOCT1(&ct->tuplehash[dir].tuple.src.u3.ip);
1199                 map.to = NOCT1(&ct->tuplehash[!dir].tuple.dst.u3.ip);
1200         } else {
1201                 /* DNAT replies */
1202                 map.from = NOCT1(&ct->tuplehash[dir].tuple.src.u3.ip);
1203                 map.to = NOCT1(&ct->tuplehash[!dir].tuple.dst.u3.ip);
1204         }
1205
1206         if (map.from == map.to)
1207                 return NF_ACCEPT;
1208
1209         if (!snmp_parse_mangle((unsigned char *)udph + sizeof(struct udphdr),
1210                                paylen, &map, &udph->check)) {
1211                 net_warn_ratelimited("bsalg: parser failed\n");
1212                 return NF_DROP;
1213         }
1214         return NF_ACCEPT;
1215 }
1216
1217 /* We don't actually set up expectations, just adjust internal IP
1218  * addresses if this is being NATted */
1219 static int help(struct sk_buff *skb, unsigned int protoff,
1220                 struct nf_conn *ct,
1221                 enum ip_conntrack_info ctinfo)
1222 {
1223         int dir = CTINFO2DIR(ctinfo);
1224         unsigned int ret;
1225         const struct iphdr *iph = ip_hdr(skb);
1226         const struct udphdr *udph = (struct udphdr *)((__be32 *)iph + iph->ihl);
1227
1228         /* SNMP replies and originating SNMP traps get mangled */
1229         if (udph->source == htons(SNMP_PORT) && dir != IP_CT_DIR_REPLY)
1230                 return NF_ACCEPT;
1231         if (udph->dest == htons(SNMP_TRAP_PORT) && dir != IP_CT_DIR_ORIGINAL)
1232                 return NF_ACCEPT;
1233
1234         /* No NAT? */
1235         if (!(ct->status & IPS_NAT_MASK))
1236                 return NF_ACCEPT;
1237
1238         /*
1239          * Make sure the packet length is ok.  So far, we were only guaranteed
1240          * to have a valid length IP header plus 8 bytes, which means we have
1241          * enough room for a UDP header.  Just verify the UDP length field so we
1242          * can mess around with the payload.
1243          */
1244         if (ntohs(udph->len) != skb->len - (iph->ihl << 2)) {
1245                 net_warn_ratelimited("SNMP: dropping malformed packet src=%pI4 dst=%pI4\n",
1246                                      &iph->saddr, &iph->daddr);
1247                  return NF_DROP;
1248         }
1249
1250         if (!skb_make_writable(skb, skb->len))
1251                 return NF_DROP;
1252
1253         spin_lock_bh(&snmp_lock);
1254         ret = snmp_translate(ct, ctinfo, skb);
1255         spin_unlock_bh(&snmp_lock);
1256         return ret;
1257 }
1258
1259 static const struct nf_conntrack_expect_policy snmp_exp_policy = {
1260         .max_expected   = 0,
1261         .timeout        = 180,
1262 };
1263
1264 static struct nf_conntrack_helper snmp_helper __read_mostly = {
1265         .me                     = THIS_MODULE,
1266         .help                   = help,
1267         .expect_policy          = &snmp_exp_policy,
1268         .name                   = "snmp",
1269         .tuple.src.l3num        = AF_INET,
1270         .tuple.src.u.udp.port   = cpu_to_be16(SNMP_PORT),
1271         .tuple.dst.protonum     = IPPROTO_UDP,
1272 };
1273
1274 static struct nf_conntrack_helper snmp_trap_helper __read_mostly = {
1275         .me                     = THIS_MODULE,
1276         .help                   = help,
1277         .expect_policy          = &snmp_exp_policy,
1278         .name                   = "snmp_trap",
1279         .tuple.src.l3num        = AF_INET,
1280         .tuple.src.u.udp.port   = cpu_to_be16(SNMP_TRAP_PORT),
1281         .tuple.dst.protonum     = IPPROTO_UDP,
1282 };
1283
1284 /*****************************************************************************
1285  *
1286  * Module stuff.
1287  *
1288  *****************************************************************************/
1289
1290 static int __init nf_nat_snmp_basic_init(void)
1291 {
1292         int ret = 0;
1293
1294         BUG_ON(nf_nat_snmp_hook != NULL);
1295         RCU_INIT_POINTER(nf_nat_snmp_hook, help);
1296
1297         ret = nf_conntrack_helper_register(&snmp_trap_helper);
1298         if (ret < 0) {
1299                 nf_conntrack_helper_unregister(&snmp_helper);
1300                 return ret;
1301         }
1302         return ret;
1303 }
1304
1305 static void __exit nf_nat_snmp_basic_fini(void)
1306 {
1307         RCU_INIT_POINTER(nf_nat_snmp_hook, NULL);
1308         nf_conntrack_helper_unregister(&snmp_trap_helper);
1309 }
1310
1311 module_init(nf_nat_snmp_basic_init);
1312 module_exit(nf_nat_snmp_basic_fini);
1313
1314 module_param(debug, int, 0600);