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/slab.h>
  47 #include <linux/in.h>
  48 #include <linux/ip.h>
  49 #include <linux/udp.h>
  50 #include <net/checksum.h>
  51 #include <net/udp.h>
  52
  53 #include <net/netfilter/nf_nat.h>
  54 #include <net/netfilter/nf_conntrack_expect.h>
  55 #include <net/netfilter/nf_conntrack_helper.h>
  56 #include <net/netfilter/nf_nat_helper.h>
  57 #include <linux/netfilter/nf_conntrack_snmp.h>
  58
  59 MODULE_LICENSE("GPL");
  60 MODULE_AUTHOR("James Morris <jmorris@intercode.com.au>");
  61 MODULE_DESCRIPTION("Basic SNMP Application Layer Gateway");
  62 MODULE_ALIAS("ip_nat_snmp_basic");
  63
  64 #define SNMP_PORT 161
  65 #define SNMP_TRAP_PORT 162
  66 #define NOCT1(n) (*(u8 *)(n))
  67
  68 static int debug;
  69 static DEFINE_SPINLOCK(snmp_lock);
  70
  71 /*
  72  * Application layer address mapping mimics the NAT mapping, but
  73  * only for the first octet in this case (a more flexible system
  74  * can be implemented if needed).
  75  */
  76 struct oct1_map
  77 {
  78         u_int8_t from;
  79         u_int8_t to;
  80 };
  81
  82
  83 /*****************************************************************************
  84  *
  85  * Basic ASN.1 decoding routines (gxsnmp author Dirk Wisse)
  86  *
  87  *****************************************************************************/
  88
  89 /* Class */
  90 #define ASN1_UNI        0       /* Universal */
  91 #define ASN1_APL        1       /* Application */
  92 #define ASN1_CTX        2       /* Context */
  93 #define ASN1_PRV        3       /* Private */
  94
  95 /* Tag */
  96 #define ASN1_EOC        0       /* End Of Contents */
  97 #define ASN1_BOL        1       /* Boolean */
  98 #define ASN1_INT        2       /* Integer */
  99 #define ASN1_BTS        3       /* Bit String */
 100 #define ASN1_OTS        4       /* Octet String */
 101 #define ASN1_NUL        5       /* Null */
 102 #define ASN1_OJI        6       /* Object Identifier  */
 103 #define ASN1_OJD        7       /* Object Description */
 104 #define ASN1_EXT        8       /* External */
 105 #define ASN1_SEQ        16      /* Sequence */
 106 #define ASN1_SET        17      /* Set */
 107 #define ASN1_NUMSTR     18      /* Numerical String */
 108 #define ASN1_PRNSTR     19      /* Printable String */
 109 #define ASN1_TEXSTR     20      /* Teletext String */
 110 #define ASN1_VIDSTR     21      /* Video String */
 111 #define ASN1_IA5STR     22      /* IA5 String */
 112 #define ASN1_UNITIM     23      /* Universal Time */
 113 #define ASN1_GENTIM     24      /* General Time */
 114 #define ASN1_GRASTR     25      /* Graphical String */
 115 #define ASN1_VISSTR     26      /* Visible String */
 116 #define ASN1_GENSTR     27      /* General String */
 117
 118 /* Primitive / Constructed methods*/
 119 #define ASN1_PRI        0       /* Primitive */
 120 #define ASN1_CON        1       /* Constructed */
 121
 122 /*
 123  * Error codes.
 124  */
 125 #define ASN1_ERR_NOERROR                0
 126 #define ASN1_ERR_DEC_EMPTY              2
 127 #define ASN1_ERR_DEC_EOC_MISMATCH       3
 128 #define ASN1_ERR_DEC_LENGTH_MISMATCH    4
 129 #define ASN1_ERR_DEC_BADVALUE           5
 130
 131 /*
 132  * ASN.1 context.
 133  */
 134 struct asn1_ctx
 135 {
 136         int error;                      /* Error condition */
 137         unsigned char *pointer;         /* Octet just to be decoded */
 138         unsigned char *begin;           /* First octet */
 139         unsigned char *end;             /* Octet after last octet */
 140 };
 141
 142 /*
 143  * Octet string (not null terminated)
 144  */
 145 struct asn1_octstr
 146 {
 147         unsigned char *data;
 148         unsigned int len;
 149 };
 150
 151 static void asn1_open(struct asn1_ctx *ctx,
 152                       unsigned char *buf,
 153                       unsigned int len)
 154 {
 155         ctx->begin = buf;
 156         ctx->end = buf + len;
 157         ctx->pointer = buf;
 158         ctx->error = ASN1_ERR_NOERROR;
 159 }
 160
 161 static unsigned char asn1_octet_decode(struct asn1_ctx *ctx, unsigned char *ch)
 162 {
 163         if (ctx->pointer >= ctx->end) {
 164                 ctx->error = ASN1_ERR_DEC_EMPTY;
 165                 return 0;
 166         }
 167         *ch = *(ctx->pointer)++;
 168         return 1;
 169 }
 170
 171 static unsigned char asn1_tag_decode(struct asn1_ctx *ctx, unsigned int *tag)
 172 {
 173         unsigned char ch;
 174
 175         *tag = 0;
 176
 177         do
 178         {
 179                 if (!asn1_octet_decode(ctx, &ch))
 180                         return 0;
 181                 *tag <<= 7;
 182                 *tag |= ch & 0x7F;
 183         } while ((ch & 0x80) == 0x80);
 184         return 1;
 185 }
 186
 187 static unsigned char asn1_id_decode(struct asn1_ctx *ctx,
 188                                     unsigned int *cls,
 189                                     unsigned int *con,
 190                                     unsigned int *tag)
 191 {
 192         unsigned char ch;
 193
 194         if (!asn1_octet_decode(ctx, &ch))
 195                 return 0;
 196
 197         *cls = (ch & 0xC0) >> 6;
 198         *con = (ch & 0x20) >> 5;
 199         *tag = (ch & 0x1F);
 200
 201         if (*tag == 0x1F) {
 202                 if (!asn1_tag_decode(ctx, tag))
 203                         return 0;
 204         }
 205         return 1;
 206 }
 207
 208 static unsigned char asn1_length_decode(struct asn1_ctx *ctx,
 209                                         unsigned int *def,
 210                                         unsigned int *len)
 211 {
 212         unsigned char ch, cnt;
 213
 214         if (!asn1_octet_decode(ctx, &ch))
 215                 return 0;
 216
 217         if (ch == 0x80)
 218                 *def = 0;
 219         else {
 220                 *def = 1;
 221
 222                 if (ch < 0x80)
 223                         *len = ch;
 224                 else {
 225                         cnt = ch & 0x7F;
 226                         *len = 0;
 227
 228                         while (cnt > 0) {
 229                                 if (!asn1_octet_decode(ctx, &ch))
 230                                         return 0;
 231                                 *len <<= 8;
 232                                 *len |= ch;
 233                                 cnt--;
 234                         }
 235                 }
 236         }
 237
 238         /* don't trust len bigger than ctx buffer */
 239         if (*len > ctx->end - ctx->pointer)
 240                 return 0;
 241
 242         return 1;
 243 }
 244
 245 static unsigned char asn1_header_decode(struct asn1_ctx *ctx,
 246                                         unsigned char **eoc,
 247                                         unsigned int *cls,
 248                                         unsigned int *con,
 249                                         unsigned int *tag)
 250 {
 251         unsigned int def, len;
 252
 253         if (!asn1_id_decode(ctx, cls, con, tag))
 254                 return 0;
 255
 256         def = len = 0;
 257         if (!asn1_length_decode(ctx, &def, &len))
 258                 return 0;
 259
 260         /* primitive shall be definite, indefinite shall be constructed */
 261         if (*con == ASN1_PRI && !def)
 262                 return 0;
 263
 264         if (def)
 265                 *eoc = ctx->pointer + len;
 266         else
 267                 *eoc = NULL;
 268         return 1;
 269 }
 270
 271 static unsigned char asn1_eoc_decode(struct asn1_ctx *ctx, unsigned char *eoc)
 272 {
 273         unsigned char ch;
 274
 275         if (eoc == NULL) {
 276                 if (!asn1_octet_decode(ctx, &ch))
 277                         return 0;
 278
 279                 if (ch != 0x00) {
 280                         ctx->error = ASN1_ERR_DEC_EOC_MISMATCH;
 281                         return 0;
 282                 }
 283
 284                 if (!asn1_octet_decode(ctx, &ch))
 285                         return 0;
 286
 287                 if (ch != 0x00) {
 288                         ctx->error = ASN1_ERR_DEC_EOC_MISMATCH;
 289                         return 0;
 290                 }
 291                 return 1;
 292         } else {
 293                 if (ctx->pointer != eoc) {
 294                         ctx->error = ASN1_ERR_DEC_LENGTH_MISMATCH;
 295                         return 0;
 296                 }
 297                 return 1;
 298         }
 299 }
 300
 301 static unsigned char asn1_null_decode(struct asn1_ctx *ctx, unsigned char *eoc)
 302 {
 303         ctx->pointer = eoc;
 304         return 1;
 305 }
 306
 307 static unsigned char asn1_long_decode(struct asn1_ctx *ctx,
 308                                       unsigned char *eoc,
 309                                       long *integer)
 310 {
 311         unsigned char ch;
 312         unsigned int  len;
 313
 314         if (!asn1_octet_decode(ctx, &ch))
 315                 return 0;
 316
 317         *integer = (signed char) ch;
 318         len = 1;
 319
 320         while (ctx->pointer < eoc) {
 321                 if (++len > sizeof (long)) {
 322                         ctx->error = ASN1_ERR_DEC_BADVALUE;
 323                         return 0;
 324                 }
 325
 326                 if (!asn1_octet_decode(ctx, &ch))
 327                         return 0;
 328
 329                 *integer <<= 8;
 330                 *integer |= ch;
 331         }
 332         return 1;
 333 }
 334
 335 static unsigned char asn1_uint_decode(struct asn1_ctx *ctx,
 336                                       unsigned char *eoc,
 337                                       unsigned int *integer)
 338 {
 339         unsigned char ch;
 340         unsigned int  len;
 341
 342         if (!asn1_octet_decode(ctx, &ch))
 343                 return 0;
 344
 345         *integer = ch;
 346         if (ch == 0) len = 0;
 347         else len = 1;
 348
 349         while (ctx->pointer < eoc) {
 350                 if (++len > sizeof (unsigned int)) {
 351                         ctx->error = ASN1_ERR_DEC_BADVALUE;
 352                         return 0;
 353                 }
 354
 355                 if (!asn1_octet_decode(ctx, &ch))
 356                         return 0;
 357
 358                 *integer <<= 8;
 359                 *integer |= ch;
 360         }
 361         return 1;
 362 }
 363
 364 static unsigned char asn1_ulong_decode(struct asn1_ctx *ctx,
 365                                        unsigned char *eoc,
 366                                        unsigned long *integer)
 367 {
 368         unsigned char ch;
 369         unsigned int  len;
 370
 371         if (!asn1_octet_decode(ctx, &ch))
 372                 return 0;
 373
 374         *integer = ch;
 375         if (ch == 0) len = 0;
 376         else len = 1;
 377
 378         while (ctx->pointer < eoc) {
 379                 if (++len > sizeof (unsigned long)) {
 380                         ctx->error = ASN1_ERR_DEC_BADVALUE;
 381                         return 0;
 382                 }
 383
 384                 if (!asn1_octet_decode(ctx, &ch))
 385                         return 0;
 386
 387                 *integer <<= 8;
 388                 *integer |= ch;
 389         }
 390         return 1;
 391 }
 392
 393 static unsigned char asn1_octets_decode(struct asn1_ctx *ctx,
 394                                         unsigned char *eoc,
 395                                         unsigned char **octets,
 396                                         unsigned int *len)
 397 {
 398         unsigned char *ptr;
 399
 400         *len = 0;
 401
 402         *octets = kmalloc(eoc - ctx->pointer, GFP_ATOMIC);
 403         if (*octets == NULL) {
 404                 if (net_ratelimit())
 405                         pr_notice("OOM in bsalg (%d)\n", __LINE__);
 406                 return 0;
 407         }
 408
 409         ptr = *octets;
 410         while (ctx->pointer < eoc) {
 411                 if (!asn1_octet_decode(ctx, (unsigned char *)ptr++)) {
 412                         kfree(*octets);
 413                         *octets = NULL;
 414                         return 0;
 415                 }
 416                 (*len)++;
 417         }
 418         return 1;
 419 }
 420
 421 static unsigned char asn1_subid_decode(struct asn1_ctx *ctx,
 422                                        unsigned long *subid)
 423 {
 424         unsigned char ch;
 425
 426         *subid = 0;
 427
 428         do {
 429                 if (!asn1_octet_decode(ctx, &ch))
 430                         return 0;
 431
 432                 *subid <<= 7;
 433                 *subid |= ch & 0x7F;
 434         } while ((ch & 0x80) == 0x80);
 435         return 1;
 436 }
 437
 438 static unsigned char asn1_oid_decode(struct asn1_ctx *ctx,
 439                                      unsigned char *eoc,
 440                                      unsigned long **oid,
 441                                      unsigned int *len)
 442 {
 443         unsigned long subid;
 444         unsigned long *optr;
 445         size_t size;
 446
 447         size = eoc - ctx->pointer + 1;
 448
 449         /* first subid actually encodes first two subids */
 450         if (size < 2 || size > ULONG_MAX/sizeof(unsigned long))
 451                 return 0;
 452
 453         *oid = kmalloc(size * sizeof(unsigned long), GFP_ATOMIC);
 454         if (*oid == NULL) {
 455                 if (net_ratelimit())
 456                         pr_notice("OOM in bsalg (%d)\n", __LINE__);
 457                 return 0;
 458         }
 459
 460         optr = *oid;
 461
 462         if (!asn1_subid_decode(ctx, &subid)) {
 463                 kfree(*oid);
 464                 *oid = NULL;
 465                 return 0;
 466         }
 467
 468         if (subid < 40) {
 469                 optr [0] = 0;
 470                 optr [1] = subid;
 471         } else if (subid < 80) {
 472                 optr [0] = 1;
 473                 optr [1] = subid - 40;
 474         } else {
 475                 optr [0] = 2;
 476                 optr [1] = subid - 80;
 477         }
 478
 479         *len = 2;
 480         optr += 2;
 481
 482         while (ctx->pointer < eoc) {
 483                 if (++(*len) > size) {
 484                         ctx->error = ASN1_ERR_DEC_BADVALUE;
 485                         kfree(*oid);
 486                         *oid = NULL;
 487                         return 0;
 488                 }
 489
 490                 if (!asn1_subid_decode(ctx, optr++)) {
 491                         kfree(*oid);
 492                         *oid = NULL;
 493                         return 0;
 494                 }
 495         }
 496         return 1;
 497 }
 498
 499 /*****************************************************************************
 500  *
 501  * SNMP decoding routines (gxsnmp author Dirk Wisse)
 502  *
 503  *****************************************************************************/
 504
 505 /* SNMP Versions */
 506 #define SNMP_V1                         0
 507 #define SNMP_V2C                        1
 508 #define SNMP_V2                         2
 509 #define SNMP_V3                         3
 510
 511 /* Default Sizes */
 512 #define SNMP_SIZE_COMM                  256
 513 #define SNMP_SIZE_OBJECTID              128
 514 #define SNMP_SIZE_BUFCHR                256
 515 #define SNMP_SIZE_BUFINT                128
 516 #define SNMP_SIZE_SMALLOBJECTID         16
 517
 518 /* Requests */
 519 #define SNMP_PDU_GET                    0
 520 #define SNMP_PDU_NEXT                   1
 521 #define SNMP_PDU_RESPONSE               2
 522 #define SNMP_PDU_SET                    3
 523 #define SNMP_PDU_TRAP1                  4
 524 #define SNMP_PDU_BULK                   5
 525 #define SNMP_PDU_INFORM                 6
 526 #define SNMP_PDU_TRAP2                  7
 527
 528 /* Errors */
 529 #define SNMP_NOERROR                    0
 530 #define SNMP_TOOBIG                     1
 531 #define SNMP_NOSUCHNAME                 2
 532 #define SNMP_BADVALUE                   3
 533 #define SNMP_READONLY                   4
 534 #define SNMP_GENERROR                   5
 535 #define SNMP_NOACCESS                   6
 536 #define SNMP_WRONGTYPE                  7
 537 #define SNMP_WRONGLENGTH                8
 538 #define SNMP_WRONGENCODING              9
 539 #define SNMP_WRONGVALUE                 10
 540 #define SNMP_NOCREATION                 11
 541 #define SNMP_INCONSISTENTVALUE          12
 542 #define SNMP_RESOURCEUNAVAILABLE        13
 543 #define SNMP_COMMITFAILED               14
 544 #define SNMP_UNDOFAILED                 15
 545 #define SNMP_AUTHORIZATIONERROR         16
 546 #define SNMP_NOTWRITABLE                17
 547 #define SNMP_INCONSISTENTNAME           18
 548
 549 /* General SNMP V1 Traps */
 550 #define SNMP_TRAP_COLDSTART             0
 551 #define SNMP_TRAP_WARMSTART             1
 552 #define SNMP_TRAP_LINKDOWN              2
 553 #define SNMP_TRAP_LINKUP                3
 554 #define SNMP_TRAP_AUTFAILURE            4
 555 #define SNMP_TRAP_EQPNEIGHBORLOSS       5
 556 #define SNMP_TRAP_ENTSPECIFIC           6
 557
 558 /* SNMPv1 Types */
 559 #define SNMP_NULL                0
 560 #define SNMP_INTEGER             1    /* l  */
 561 #define SNMP_OCTETSTR            2    /* c  */
 562 #define SNMP_DISPLAYSTR          2    /* c  */
 563 #define SNMP_OBJECTID            3    /* ul */
 564 #define SNMP_IPADDR              4    /* uc */
 565 #define SNMP_COUNTER             5    /* ul */
 566 #define SNMP_GAUGE               6    /* ul */
 567 #define SNMP_TIMETICKS           7    /* ul */
 568 #define SNMP_OPAQUE              8    /* c  */
 569
 570 /* Additional SNMPv2 Types */
 571 #define SNMP_UINTEGER            5    /* ul */
 572 #define SNMP_BITSTR              9    /* uc */
 573 #define SNMP_NSAP               10    /* uc */
 574 #define SNMP_COUNTER64          11    /* ul */
 575 #define SNMP_NOSUCHOBJECT       12
 576 #define SNMP_NOSUCHINSTANCE     13
 577 #define SNMP_ENDOFMIBVIEW       14
 578
 579 union snmp_syntax
 580 {
 581         unsigned char uc[0];    /* 8 bit unsigned */
 582         char c[0];              /* 8 bit signed */
 583         unsigned long ul[0];    /* 32 bit unsigned */
 584         long l[0];              /* 32 bit signed */
 585 };
 586
 587 struct snmp_object
 588 {
 589         unsigned long *id;
 590         unsigned int id_len;
 591         unsigned short type;
 592         unsigned int syntax_len;
 593         union snmp_syntax syntax;
 594 };
 595
 596 struct snmp_request
 597 {
 598         unsigned long id;
 599         unsigned int error_status;
 600         unsigned int error_index;
 601 };
 602
 603 struct snmp_v1_trap
 604 {
 605         unsigned long *id;
 606         unsigned int id_len;
 607         unsigned long ip_address;       /* pointer  */
 608         unsigned int general;
 609         unsigned int specific;
 610         unsigned long time;
 611 };
 612
 613 /* SNMP types */
 614 #define SNMP_IPA    0
 615 #define SNMP_CNT    1
 616 #define SNMP_GGE    2
 617 #define SNMP_TIT    3
 618 #define SNMP_OPQ    4
 619 #define SNMP_C64    6
 620
 621 /* SNMP errors */
 622 #define SERR_NSO    0
 623 #define SERR_NSI    1
 624 #define SERR_EOM    2
 625
 626 static inline void mangle_address(unsigned char *begin,
 627                                   unsigned char *addr,
 628                                   const struct oct1_map *map,
 629                                   __sum16 *check);
 630 struct snmp_cnv
 631 {
 632         unsigned int class;
 633         unsigned int tag;
 634         int syntax;
 635 };
 636
 637 static const struct snmp_cnv snmp_conv[] = {
 638         {ASN1_UNI, ASN1_NUL, SNMP_NULL},
 639         {ASN1_UNI, ASN1_INT, SNMP_INTEGER},
 640         {ASN1_UNI, ASN1_OTS, SNMP_OCTETSTR},
 641         {ASN1_UNI, ASN1_OTS, SNMP_DISPLAYSTR},
 642         {ASN1_UNI, ASN1_OJI, SNMP_OBJECTID},
 643         {ASN1_APL, SNMP_IPA, SNMP_IPADDR},
 644         {ASN1_APL, SNMP_CNT, SNMP_COUNTER},     /* Counter32 */
 645         {ASN1_APL, SNMP_GGE, SNMP_GAUGE},       /* Gauge32 == Unsigned32  */
 646         {ASN1_APL, SNMP_TIT, SNMP_TIMETICKS},
 647         {ASN1_APL, SNMP_OPQ, SNMP_OPAQUE},
 648
 649         /* SNMPv2 data types and errors */
 650         {ASN1_UNI, ASN1_BTS, SNMP_BITSTR},
 651         {ASN1_APL, SNMP_C64, SNMP_COUNTER64},
 652         {ASN1_CTX, SERR_NSO, SNMP_NOSUCHOBJECT},
 653         {ASN1_CTX, SERR_NSI, SNMP_NOSUCHINSTANCE},
 654         {ASN1_CTX, SERR_EOM, SNMP_ENDOFMIBVIEW},
 655         {0,       0,       -1}
 656 };
 657
 658 static unsigned char snmp_tag_cls2syntax(unsigned int tag,
 659                                          unsigned int cls,
 660                                          unsigned short *syntax)
 661 {
 662         const struct snmp_cnv *cnv;
 663
 664         cnv = snmp_conv;
 665
 666         while (cnv->syntax != -1) {
 667                 if (cnv->tag == tag && cnv->class == cls) {
 668                         *syntax = cnv->syntax;
 669                         return 1;
 670                 }
 671                 cnv++;
 672         }
 673         return 0;
 674 }
 675
 676 static unsigned char snmp_object_decode(struct asn1_ctx *ctx,
 677                                         struct snmp_object **obj)
 678 {
 679         unsigned int cls, con, tag, len, idlen;
 680         unsigned short type;
 681         unsigned char *eoc, *end, *p;
 682         unsigned long *lp, *id;
 683         unsigned long ul;
 684         long l;
 685
 686         *obj = NULL;
 687         id = NULL;
 688
 689         if (!asn1_header_decode(ctx, &eoc, &cls, &con, &tag))
 690                 return 0;
 691
 692         if (cls != ASN1_UNI || con != ASN1_CON || tag != ASN1_SEQ)
 693                 return 0;
 694
 695         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 696                 return 0;
 697
 698         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_OJI)
 699                 return 0;
 700
 701         if (!asn1_oid_decode(ctx, end, &id, &idlen))
 702                 return 0;
 703
 704         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag)) {
 705                 kfree(id);
 706                 return 0;
 707         }
 708
 709         if (con != ASN1_PRI) {
 710                 kfree(id);
 711                 return 0;
 712         }
 713
 714         type = 0;
 715         if (!snmp_tag_cls2syntax(tag, cls, &type)) {
 716                 kfree(id);
 717                 return 0;
 718         }
 719
 720         l = 0;
 721         switch (type) {
 722                 case SNMP_INTEGER:
 723                         len = sizeof(long);
 724                         if (!asn1_long_decode(ctx, end, &l)) {
 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                                         pr_notice("OOM in bsalg (%d)\n", __LINE__);
 734                                 return 0;
 735                         }
 736                         (*obj)->syntax.l[0] = l;
 737                         break;
 738                 case SNMP_OCTETSTR:
 739                 case SNMP_OPAQUE:
 740                         if (!asn1_octets_decode(ctx, end, &p, &len)) {
 741                                 kfree(id);
 742                                 return 0;
 743                         }
 744                         *obj = kmalloc(sizeof(struct snmp_object) + len,
 745                                        GFP_ATOMIC);
 746                         if (*obj == NULL) {
 747                                 kfree(p);
 748                                 kfree(id);
 749                                 if (net_ratelimit())
 750                                         pr_notice("OOM in bsalg (%d)\n", __LINE__);
 751                                 return 0;
 752                         }
 753                         memcpy((*obj)->syntax.c, p, len);
 754                         kfree(p);
 755                         break;
 756                 case SNMP_NULL:
 757                 case SNMP_NOSUCHOBJECT:
 758                 case SNMP_NOSUCHINSTANCE:
 759                 case SNMP_ENDOFMIBVIEW:
 760                         len = 0;
 761                         *obj = kmalloc(sizeof(struct snmp_object), GFP_ATOMIC);
 762                         if (*obj == NULL) {
 763                                 kfree(id);
 764                                 if (net_ratelimit())
 765                                         pr_notice("OOM in bsalg (%d)\n", __LINE__);
 766                                 return 0;
 767                         }
 768                         if (!asn1_null_decode(ctx, end)) {
 769                                 kfree(id);
 770                                 kfree(*obj);
 771                                 *obj = NULL;
 772                                 return 0;
 773                         }
 774                         break;
 775                 case SNMP_OBJECTID:
 776                         if (!asn1_oid_decode(ctx, end, (unsigned long **)&lp, &len)) {
 777                                 kfree(id);
 778                                 return 0;
 779                         }
 780                         len *= sizeof(unsigned long);
 781                         *obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
 782                         if (*obj == NULL) {
 783                                 kfree(lp);
 784                                 kfree(id);
 785                                 if (net_ratelimit())
 786                                         pr_notice("OOM in bsalg (%d)\n", __LINE__);
 787                                 return 0;
 788                         }
 789                         memcpy((*obj)->syntax.ul, lp, len);
 790                         kfree(lp);
 791                         break;
 792                 case SNMP_IPADDR:
 793                         if (!asn1_octets_decode(ctx, end, &p, &len)) {
 794                                 kfree(id);
 795                                 return 0;
 796                         }
 797                         if (len != 4) {
 798                                 kfree(p);
 799                                 kfree(id);
 800                                 return 0;
 801                         }
 802                         *obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
 803                         if (*obj == NULL) {
 804                                 kfree(p);
 805                                 kfree(id);
 806                                 if (net_ratelimit())
 807                                         pr_notice("OOM in bsalg (%d)\n", __LINE__);
 808                                 return 0;
 809                         }
 810                         memcpy((*obj)->syntax.uc, p, len);
 811                         kfree(p);
 812                         break;
 813                 case SNMP_COUNTER:
 814                 case SNMP_GAUGE:
 815                 case SNMP_TIMETICKS:
 816                         len = sizeof(unsigned long);
 817                         if (!asn1_ulong_decode(ctx, end, &ul)) {
 818                                 kfree(id);
 819                                 return 0;
 820                         }
 821                         *obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
 822                         if (*obj == NULL) {
 823                                 kfree(id);
 824                                 if (net_ratelimit())
 825                                         pr_notice("OOM in bsalg (%d)\n", __LINE__);
 826                                 return 0;
 827                         }
 828                         (*obj)->syntax.ul[0] = ul;
 829                         break;
 830                 default:
 831                         kfree(id);
 832                         return 0;
 833         }
 834
 835         (*obj)->syntax_len = len;
 836         (*obj)->type = type;
 837         (*obj)->id = id;
 838         (*obj)->id_len = idlen;
 839
 840         if (!asn1_eoc_decode(ctx, eoc)) {
 841                 kfree(id);
 842                 kfree(*obj);
 843                 *obj = NULL;
 844                 return 0;
 845         }
 846         return 1;
 847 }
 848
 849 static unsigned char snmp_request_decode(struct asn1_ctx *ctx,
 850                                          struct snmp_request *request)
 851 {
 852         unsigned int cls, con, tag;
 853         unsigned char *end;
 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_ulong_decode(ctx, end, &request->id))
 862                 return 0;
 863
 864         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 865                 return 0;
 866
 867         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
 868                 return 0;
 869
 870         if (!asn1_uint_decode(ctx, end, &request->error_status))
 871                 return 0;
 872
 873         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 874                 return 0;
 875
 876         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
 877                 return 0;
 878
 879         if (!asn1_uint_decode(ctx, end, &request->error_index))
 880                 return 0;
 881
 882         return 1;
 883 }
 884
 885 /*
 886  * Fast checksum update for possibly oddly-aligned UDP byte, from the
 887  * code example in the draft.
 888  */
 889 static void fast_csum(__sum16 *csum,
 890                       const unsigned char *optr,
 891                       const unsigned char *nptr,
 892                       int offset)
 893 {
 894         unsigned char s[4];
 895
 896         if (offset & 1) {
 897                 s[0] = ~0;
 898                 s[1] = ~*optr;
 899                 s[2] = 0;
 900                 s[3] = *nptr;
 901         } else {
 902                 s[0] = ~*optr;
 903                 s[1] = ~0;
 904                 s[2] = *nptr;
 905                 s[3] = 0;
 906         }
 907
 908         *csum = csum_fold(csum_partial(s, 4, ~csum_unfold(*csum)));
 909 }
 910
 911 /*
 912  * Mangle IP address.
 913  *      - begin points to the start of the snmp messgae
 914  *      - addr points to the start of the address
 915  */
 916 static inline void mangle_address(unsigned char *begin,
 917                                   unsigned char *addr,
 918                                   const struct oct1_map *map,
 919                                   __sum16 *check)
 920 {
 921         if (map->from == NOCT1(addr)) {
 922                 u_int32_t old;
 923
 924                 if (debug)
 925                         memcpy(&old, addr, sizeof(old));
 926
 927                 *addr = map->to;
 928
 929                 /* Update UDP checksum if being used */
 930                 if (*check) {
 931                         fast_csum(check,
 932                                   &map->from, &map->to, addr - begin);
 933
 934                 }
 935
 936                 if (debug)
 937                         printk(KERN_DEBUG "bsalg: mapped %pI4 to %pI4\n",
 938                                &old, addr);
 939         }
 940 }
 941
 942 static unsigned char snmp_trap_decode(struct asn1_ctx *ctx,
 943                                       struct snmp_v1_trap *trap,
 944                                       const struct oct1_map *map,
 945                                       __sum16 *check)
 946 {
 947         unsigned int cls, con, tag, len;
 948         unsigned char *end;
 949
 950         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 951                 return 0;
 952
 953         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_OJI)
 954                 return 0;
 955
 956         if (!asn1_oid_decode(ctx, end, &trap->id, &trap->id_len))
 957                 return 0;
 958
 959         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 960                 goto err_id_free;
 961
 962         if (!((cls == ASN1_APL && con == ASN1_PRI && tag == SNMP_IPA) ||
 963               (cls == ASN1_UNI && con == ASN1_PRI && tag == ASN1_OTS)))
 964                 goto err_id_free;
 965
 966         if (!asn1_octets_decode(ctx, end, (unsigned char **)&trap->ip_address, &len))
 967                 goto err_id_free;
 968
 969         /* IPv4 only */
 970         if (len != 4)
 971                 goto err_addr_free;
 972
 973         mangle_address(ctx->begin, ctx->pointer - 4, map, check);
 974
 975         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 976                 goto err_addr_free;
 977
 978         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
 979                 goto err_addr_free;
 980
 981         if (!asn1_uint_decode(ctx, end, &trap->general))
 982                 goto err_addr_free;
 983
 984         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 985                 goto err_addr_free;
 986
 987         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
 988                 goto err_addr_free;
 989
 990         if (!asn1_uint_decode(ctx, end, &trap->specific))
 991                 goto err_addr_free;
 992
 993         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 994                 goto err_addr_free;
 995
 996         if (!((cls == ASN1_APL && con == ASN1_PRI && tag == SNMP_TIT) ||
 997               (cls == ASN1_UNI && con == ASN1_PRI && tag == ASN1_INT)))
 998                 goto err_addr_free;
 999
1000         if (!asn1_ulong_decode(ctx, end, &trap->time))
1001                 goto err_addr_free;
1002
1003         return 1;
1004
1005 err_addr_free:
1006         kfree((unsigned long *)trap->ip_address);
1007
1008 err_id_free:
1009         kfree(trap->id);
1010
1011         return 0;
1012 }
1013
1014 /*****************************************************************************
1015  *
1016  * Misc. routines
1017  *
1018  *****************************************************************************/
1019
1020 static void hex_dump(const unsigned char *buf, size_t len)
1021 {
1022         size_t i;
1023
1024         for (i = 0; i < len; i++) {
1025                 if (i && !(i % 16))
1026                         printk("\n");
1027                 printk("%02x ", *(buf + i));
1028         }
1029         printk("\n");
1030 }
1031
1032 /*
1033  * Parse and mangle SNMP message according to mapping.
1034  * (And this is the fucking 'basic' method).
1035  */
1036 static int snmp_parse_mangle(unsigned char *msg,
1037                              u_int16_t len,
1038                              const struct oct1_map *map,
1039                              __sum16 *check)
1040 {
1041         unsigned char *eoc, *end;
1042         unsigned int cls, con, tag, vers, pdutype;
1043         struct asn1_ctx ctx;
1044         struct asn1_octstr comm;
1045         struct snmp_object *obj;
1046
1047         if (debug > 1)
1048                 hex_dump(msg, len);
1049
1050         asn1_open(&ctx, msg, len);
1051
1052         /*
1053          * Start of SNMP message.
1054          */
1055         if (!asn1_header_decode(&ctx, &eoc, &cls, &con, &tag))
1056                 return 0;
1057         if (cls != ASN1_UNI || con != ASN1_CON || tag != ASN1_SEQ)
1058                 return 0;
1059
1060         /*
1061          * Version 1 or 2 handled.
1062          */
1063         if (!asn1_header_decode(&ctx, &end, &cls, &con, &tag))
1064                 return 0;
1065         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
1066                 return 0;
1067         if (!asn1_uint_decode (&ctx, end, &vers))
1068                 return 0;
1069         if (debug > 1)
1070                 printk(KERN_DEBUG "bsalg: snmp version: %u\n", vers + 1);
1071         if (vers > 1)
1072                 return 1;
1073
1074         /*
1075          * Community.
1076          */
1077         if (!asn1_header_decode (&ctx, &end, &cls, &con, &tag))
1078                 return 0;
1079         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_OTS)
1080                 return 0;
1081         if (!asn1_octets_decode(&ctx, end, &comm.data, &comm.len))
1082                 return 0;
1083         if (debug > 1) {
1084                 unsigned int i;
1085
1086                 printk(KERN_DEBUG "bsalg: community: ");
1087                 for (i = 0; i < comm.len; i++)
1088                         printk("%c", comm.data[i]);
1089                 printk("\n");
1090         }
1091         kfree(comm.data);
1092
1093         /*
1094          * PDU type
1095          */
1096         if (!asn1_header_decode(&ctx, &eoc, &cls, &con, &pdutype))
1097                 return 0;
1098         if (cls != ASN1_CTX || con != ASN1_CON)
1099                 return 0;
1100         if (debug > 1) {
1101                 static const unsigned char *const pdus[] = {
1102                         [SNMP_PDU_GET] = "get",
1103                         [SNMP_PDU_NEXT] = "get-next",
1104                         [SNMP_PDU_RESPONSE] = "response",
1105                         [SNMP_PDU_SET] = "set",
1106                         [SNMP_PDU_TRAP1] = "trapv1",
1107                         [SNMP_PDU_BULK] = "bulk",
1108                         [SNMP_PDU_INFORM] = "inform",
1109                         [SNMP_PDU_TRAP2] = "trapv2"
1110                 };
1111
1112                 if (pdutype > SNMP_PDU_TRAP2)
1113                         printk(KERN_DEBUG "bsalg: bad pdu type %u\n", pdutype);
1114                 else
1115                         printk(KERN_DEBUG "bsalg: pdu: %s\n", pdus[pdutype]);
1116         }
1117         if (pdutype != SNMP_PDU_RESPONSE &&
1118             pdutype != SNMP_PDU_TRAP1 && pdutype != SNMP_PDU_TRAP2)
1119                 return 1;
1120
1121         /*
1122          * Request header or v1 trap
1123          */
1124         if (pdutype == SNMP_PDU_TRAP1) {
1125                 struct snmp_v1_trap trap;
1126                 unsigned char ret = snmp_trap_decode(&ctx, &trap, map, check);
1127
1128                 if (ret) {
1129                         kfree(trap.id);
1130                         kfree((unsigned long *)trap.ip_address);
1131                 } else
1132                         return ret;
1133
1134         } else {
1135                 struct snmp_request req;
1136
1137                 if (!snmp_request_decode(&ctx, &req))
1138                         return 0;
1139
1140                 if (debug > 1)
1141                         printk(KERN_DEBUG "bsalg: request: id=0x%lx error_status=%u "
1142                         "error_index=%u\n", req.id, req.error_status,
1143                         req.error_index);
1144         }
1145
1146         /*
1147          * Loop through objects, look for IP addresses to mangle.
1148          */
1149         if (!asn1_header_decode(&ctx, &eoc, &cls, &con, &tag))
1150                 return 0;
1151
1152         if (cls != ASN1_UNI || con != ASN1_CON || tag != ASN1_SEQ)
1153                 return 0;
1154
1155         while (!asn1_eoc_decode(&ctx, eoc)) {
1156                 unsigned int i;
1157
1158                 if (!snmp_object_decode(&ctx, &obj)) {
1159                         if (obj) {
1160                                 kfree(obj->id);
1161                                 kfree(obj);
1162                         }
1163                         return 0;
1164                 }
1165
1166                 if (debug > 1) {
1167                         printk(KERN_DEBUG "bsalg: object: ");
1168                         for (i = 0; i < obj->id_len; i++) {
1169                                 if (i > 0)
1170                                         printk(".");
1171                                 printk("%lu", obj->id[i]);
1172                         }
1173                         printk(": type=%u\n", obj->type);
1174
1175                 }
1176
1177                 if (obj->type == SNMP_IPADDR)
1178                         mangle_address(ctx.begin, ctx.pointer - 4 , map, check);
1179
1180                 kfree(obj->id);
1181                 kfree(obj);
1182         }
1183
1184         if (!asn1_eoc_decode(&ctx, eoc))
1185                 return 0;
1186
1187         return 1;
1188 }
1189
1190 /*****************************************************************************
1191  *
1192  * NAT routines.
1193  *
1194  *****************************************************************************/
1195
1196 /*
1197  * SNMP translation routine.
1198  */
1199 static int snmp_translate(struct nf_conn *ct,
1200                           enum ip_conntrack_info ctinfo,
1201                           struct sk_buff *skb)
1202 {
1203         struct iphdr *iph = ip_hdr(skb);
1204         struct udphdr *udph = (struct udphdr *)((__be32 *)iph + iph->ihl);
1205         u_int16_t udplen = ntohs(udph->len);
1206         u_int16_t paylen = udplen - sizeof(struct udphdr);
1207         int dir = CTINFO2DIR(ctinfo);
1208         struct oct1_map map;
1209
1210         /*
1211          * Determine mappping for application layer addresses based
1212          * on NAT manipulations for the packet.
1213          */
1214         if (dir == IP_CT_DIR_ORIGINAL) {
1215                 /* SNAT traps */
1216                 map.from = NOCT1(&ct->tuplehash[dir].tuple.src.u3.ip);
1217                 map.to = NOCT1(&ct->tuplehash[!dir].tuple.dst.u3.ip);
1218         } else {
1219                 /* DNAT replies */
1220                 map.from = NOCT1(&ct->tuplehash[dir].tuple.src.u3.ip);
1221                 map.to = NOCT1(&ct->tuplehash[!dir].tuple.dst.u3.ip);
1222         }
1223
1224         if (map.from == map.to)
1225                 return NF_ACCEPT;
1226
1227         if (!snmp_parse_mangle((unsigned char *)udph + sizeof(struct udphdr),
1228                                paylen, &map, &udph->check)) {
1229                 if (net_ratelimit())
1230                         printk(KERN_WARNING "bsalg: parser failed\n");
1231                 return NF_DROP;
1232         }
1233         return NF_ACCEPT;
1234 }
1235
1236 /* We don't actually set up expectations, just adjust internal IP
1237  * addresses if this is being NATted */
1238 static int help(struct sk_buff *skb, unsigned int protoff,
1239                 struct nf_conn *ct,
1240                 enum ip_conntrack_info ctinfo)
1241 {
1242         int dir = CTINFO2DIR(ctinfo);
1243         unsigned int ret;
1244         const struct iphdr *iph = ip_hdr(skb);
1245         const struct udphdr *udph = (struct udphdr *)((__be32 *)iph + iph->ihl);
1246
1247         /* SNMP replies and originating SNMP traps get mangled */
1248         if (udph->source == htons(SNMP_PORT) && dir != IP_CT_DIR_REPLY)
1249                 return NF_ACCEPT;
1250         if (udph->dest == htons(SNMP_TRAP_PORT) && dir != IP_CT_DIR_ORIGINAL)
1251                 return NF_ACCEPT;
1252
1253         /* No NAT? */
1254         if (!(ct->status & IPS_NAT_MASK))
1255                 return NF_ACCEPT;
1256
1257         /*
1258          * Make sure the packet length is ok.  So far, we were only guaranteed
1259          * to have a valid length IP header plus 8 bytes, which means we have
1260          * enough room for a UDP header.  Just verify the UDP length field so we
1261          * can mess around with the payload.
1262          */
1263         if (ntohs(udph->len) != skb->len - (iph->ihl << 2)) {
1264                  if (net_ratelimit())
1265                          printk(KERN_WARNING "SNMP: dropping malformed packet src=%pI4 dst=%pI4\n",
1266                                 &iph->saddr, &iph->daddr);
1267                  return NF_DROP;
1268         }
1269
1270         if (!skb_make_writable(skb, skb->len))
1271                 return NF_DROP;
1272
1273         spin_lock_bh(&snmp_lock);
1274         ret = snmp_translate(ct, ctinfo, skb);
1275         spin_unlock_bh(&snmp_lock);
1276         return ret;
1277 }
1278
1279 static const struct nf_conntrack_expect_policy snmp_exp_policy = {
1280         .max_expected   = 0,
1281         .timeout        = 180,
1282 };
1283
1284 static struct nf_conntrack_helper snmp_helper __read_mostly = {
1285         .me                     = THIS_MODULE,
1286         .help                   = help,
1287         .expect_policy          = &snmp_exp_policy,
1288         .name                   = "snmp",
1289         .tuple.src.l3num        = AF_INET,
1290         .tuple.src.u.udp.port   = cpu_to_be16(SNMP_PORT),
1291         .tuple.dst.protonum     = IPPROTO_UDP,
1292 };
1293
1294 static struct nf_conntrack_helper snmp_trap_helper __read_mostly = {
1295         .me                     = THIS_MODULE,
1296         .help                   = help,
1297         .expect_policy          = &snmp_exp_policy,
1298         .name                   = "snmp_trap",
1299         .tuple.src.l3num        = AF_INET,
1300         .tuple.src.u.udp.port   = cpu_to_be16(SNMP_TRAP_PORT),
1301         .tuple.dst.protonum     = IPPROTO_UDP,
1302 };
1303
1304 /*****************************************************************************
1305  *
1306  * Module stuff.
1307  *
1308  *****************************************************************************/
1309
1310 static int __init nf_nat_snmp_basic_init(void)
1311 {
1312         int ret = 0;
1313
1314         BUG_ON(nf_nat_snmp_hook != NULL);
1315         rcu_assign_pointer(nf_nat_snmp_hook, help);
1316
1317         ret = nf_conntrack_helper_register(&snmp_trap_helper);
1318         if (ret < 0) {
1319                 nf_conntrack_helper_unregister(&snmp_helper);
1320                 return ret;
1321         }
1322         return ret;
1323 }
1324
1325 static void __exit nf_nat_snmp_basic_fini(void)
1326 {
1327         rcu_assign_pointer(nf_nat_snmp_hook, NULL);
1328         nf_conntrack_helper_unregister(&snmp_trap_helper);
1329 }
1330
1331 module_init(nf_nat_snmp_basic_init);
1332 module_exit(nf_nat_snmp_basic_fini);
1333
1334 module_param(debug, int, 0600);