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, see <http://www.gnu.org/licenses/>.
  38  *
  39  * Author: James Morris <jmorris@intercode.com.au>
  40  *
  41  * Copyright (c) 2006-2010 Patrick McHardy <kaber@trash.net>
  42  */
  43 #include <linux/module.h>
  44 #include <linux/moduleparam.h>
  45 #include <linux/types.h>
  46 #include <linux/kernel.h>
  47 #include <linux/slab.h>
  48 #include <linux/in.h>
  49 #include <linux/ip.h>
  50 #include <linux/udp.h>
  51 #include <net/checksum.h>
  52 #include <net/udp.h>
  53
  54 #include <net/netfilter/nf_nat.h>
  55 #include <net/netfilter/nf_conntrack_expect.h>
  56 #include <net/netfilter/nf_conntrack_helper.h>
  57 #include <net/netfilter/nf_nat_helper.h>
  58 #include <linux/netfilter/nf_conntrack_snmp.h>
  59
  60 MODULE_LICENSE("GPL");
  61 MODULE_AUTHOR("James Morris <jmorris@intercode.com.au>");
  62 MODULE_DESCRIPTION("Basic SNMP Application Layer Gateway");
  63 MODULE_ALIAS("ip_nat_snmp_basic");
  64
  65 #define SNMP_PORT 161
  66 #define SNMP_TRAP_PORT 162
  67 #define NOCT1(n) (*(u8 *)(n))
  68
  69 static int debug;
  70 static DEFINE_SPINLOCK(snmp_lock);
  71
  72 /*
  73  * Application layer address mapping mimics the NAT mapping, but
  74  * only for the first octet in this case (a more flexible system
  75  * can be implemented if needed).
  76  */
  77 struct oct1_map
  78 {
  79         u_int8_t from;
  80         u_int8_t to;
  81 };
  82
  83
  84 /*****************************************************************************
  85  *
  86  * Basic ASN.1 decoding routines (gxsnmp author Dirk Wisse)
  87  *
  88  *****************************************************************************/
  89
  90 /* Class */
  91 #define ASN1_UNI        0       /* Universal */
  92 #define ASN1_APL        1       /* Application */
  93 #define ASN1_CTX        2       /* Context */
  94 #define ASN1_PRV        3       /* Private */
  95
  96 /* Tag */
  97 #define ASN1_EOC        0       /* End Of Contents */
  98 #define ASN1_BOL        1       /* Boolean */
  99 #define ASN1_INT        2       /* Integer */
 100 #define ASN1_BTS        3       /* Bit String */
 101 #define ASN1_OTS        4       /* Octet String */
 102 #define ASN1_NUL        5       /* Null */
 103 #define ASN1_OJI        6       /* Object Identifier  */
 104 #define ASN1_OJD        7       /* Object Description */
 105 #define ASN1_EXT        8       /* External */
 106 #define ASN1_SEQ        16      /* Sequence */
 107 #define ASN1_SET        17      /* Set */
 108 #define ASN1_NUMSTR     18      /* Numerical String */
 109 #define ASN1_PRNSTR     19      /* Printable String */
 110 #define ASN1_TEXSTR     20      /* Teletext String */
 111 #define ASN1_VIDSTR     21      /* Video String */
 112 #define ASN1_IA5STR     22      /* IA5 String */
 113 #define ASN1_UNITIM     23      /* Universal Time */
 114 #define ASN1_GENTIM     24      /* General Time */
 115 #define ASN1_GRASTR     25      /* Graphical String */
 116 #define ASN1_VISSTR     26      /* Visible String */
 117 #define ASN1_GENSTR     27      /* General String */
 118
 119 /* Primitive / Constructed methods*/
 120 #define ASN1_PRI        0       /* Primitive */
 121 #define ASN1_CON        1       /* Constructed */
 122
 123 /*
 124  * Error codes.
 125  */
 126 #define ASN1_ERR_NOERROR                0
 127 #define ASN1_ERR_DEC_EMPTY              2
 128 #define ASN1_ERR_DEC_EOC_MISMATCH       3
 129 #define ASN1_ERR_DEC_LENGTH_MISMATCH    4
 130 #define ASN1_ERR_DEC_BADVALUE           5
 131
 132 /*
 133  * ASN.1 context.
 134  */
 135 struct asn1_ctx
 136 {
 137         int error;                      /* Error condition */
 138         unsigned char *pointer;         /* Octet just to be decoded */
 139         unsigned char *begin;           /* First octet */
 140         unsigned char *end;             /* Octet after last octet */
 141 };
 142
 143 /*
 144  * Octet string (not null terminated)
 145  */
 146 struct asn1_octstr
 147 {
 148         unsigned char *data;
 149         unsigned int len;
 150 };
 151
 152 static void asn1_open(struct asn1_ctx *ctx,
 153                       unsigned char *buf,
 154                       unsigned int len)
 155 {
 156         ctx->begin = buf;
 157         ctx->end = buf + len;
 158         ctx->pointer = buf;
 159         ctx->error = ASN1_ERR_NOERROR;
 160 }
 161
 162 static unsigned char asn1_octet_decode(struct asn1_ctx *ctx, unsigned char *ch)
 163 {
 164         if (ctx->pointer >= ctx->end) {
 165                 ctx->error = ASN1_ERR_DEC_EMPTY;
 166                 return 0;
 167         }
 168         *ch = *(ctx->pointer)++;
 169         return 1;
 170 }
 171
 172 static unsigned char asn1_tag_decode(struct asn1_ctx *ctx, unsigned int *tag)
 173 {
 174         unsigned char ch;
 175
 176         *tag = 0;
 177
 178         do
 179         {
 180                 if (!asn1_octet_decode(ctx, &ch))
 181                         return 0;
 182                 *tag <<= 7;
 183                 *tag |= ch & 0x7F;
 184         } while ((ch & 0x80) == 0x80);
 185         return 1;
 186 }
 187
 188 static unsigned char asn1_id_decode(struct asn1_ctx *ctx,
 189                                     unsigned int *cls,
 190                                     unsigned int *con,
 191                                     unsigned int *tag)
 192 {
 193         unsigned char ch;
 194
 195         if (!asn1_octet_decode(ctx, &ch))
 196                 return 0;
 197
 198         *cls = (ch & 0xC0) >> 6;
 199         *con = (ch & 0x20) >> 5;
 200         *tag = (ch & 0x1F);
 201
 202         if (*tag == 0x1F) {
 203                 if (!asn1_tag_decode(ctx, tag))
 204                         return 0;
 205         }
 206         return 1;
 207 }
 208
 209 static unsigned char asn1_length_decode(struct asn1_ctx *ctx,
 210                                         unsigned int *def,
 211                                         unsigned int *len)
 212 {
 213         unsigned char ch, cnt;
 214
 215         if (!asn1_octet_decode(ctx, &ch))
 216                 return 0;
 217
 218         if (ch == 0x80)
 219                 *def = 0;
 220         else {
 221                 *def = 1;
 222
 223                 if (ch < 0x80)
 224                         *len = ch;
 225                 else {
 226                         cnt = ch & 0x7F;
 227                         *len = 0;
 228
 229                         while (cnt > 0) {
 230                                 if (!asn1_octet_decode(ctx, &ch))
 231                                         return 0;
 232                                 *len <<= 8;
 233                                 *len |= ch;
 234                                 cnt--;
 235                         }
 236                 }
 237         }
 238
 239         /* don't trust len bigger than ctx buffer */
 240         if (*len > ctx->end - ctx->pointer)
 241                 return 0;
 242
 243         return 1;
 244 }
 245
 246 static unsigned char asn1_header_decode(struct asn1_ctx *ctx,
 247                                         unsigned char **eoc,
 248                                         unsigned int *cls,
 249                                         unsigned int *con,
 250                                         unsigned int *tag)
 251 {
 252         unsigned int def, len;
 253
 254         if (!asn1_id_decode(ctx, cls, con, tag))
 255                 return 0;
 256
 257         def = len = 0;
 258         if (!asn1_length_decode(ctx, &def, &len))
 259                 return 0;
 260
 261         /* primitive shall be definite, indefinite shall be constructed */
 262         if (*con == ASN1_PRI && !def)
 263                 return 0;
 264
 265         if (def)
 266                 *eoc = ctx->pointer + len;
 267         else
 268                 *eoc = NULL;
 269         return 1;
 270 }
 271
 272 static unsigned char asn1_eoc_decode(struct asn1_ctx *ctx, unsigned char *eoc)
 273 {
 274         unsigned char ch;
 275
 276         if (eoc == NULL) {
 277                 if (!asn1_octet_decode(ctx, &ch))
 278                         return 0;
 279
 280                 if (ch != 0x00) {
 281                         ctx->error = ASN1_ERR_DEC_EOC_MISMATCH;
 282                         return 0;
 283                 }
 284
 285                 if (!asn1_octet_decode(ctx, &ch))
 286                         return 0;
 287
 288                 if (ch != 0x00) {
 289                         ctx->error = ASN1_ERR_DEC_EOC_MISMATCH;
 290                         return 0;
 291                 }
 292                 return 1;
 293         } else {
 294                 if (ctx->pointer != eoc) {
 295                         ctx->error = ASN1_ERR_DEC_LENGTH_MISMATCH;
 296                         return 0;
 297                 }
 298                 return 1;
 299         }
 300 }
 301
 302 static unsigned char asn1_null_decode(struct asn1_ctx *ctx, unsigned char *eoc)
 303 {
 304         ctx->pointer = eoc;
 305         return 1;
 306 }
 307
 308 static unsigned char asn1_long_decode(struct asn1_ctx *ctx,
 309                                       unsigned char *eoc,
 310                                       long *integer)
 311 {
 312         unsigned char ch;
 313         unsigned int  len;
 314
 315         if (!asn1_octet_decode(ctx, &ch))
 316                 return 0;
 317
 318         *integer = (signed char) ch;
 319         len = 1;
 320
 321         while (ctx->pointer < eoc) {
 322                 if (++len > sizeof (long)) {
 323                         ctx->error = ASN1_ERR_DEC_BADVALUE;
 324                         return 0;
 325                 }
 326
 327                 if (!asn1_octet_decode(ctx, &ch))
 328                         return 0;
 329
 330                 *integer <<= 8;
 331                 *integer |= ch;
 332         }
 333         return 1;
 334 }
 335
 336 static unsigned char asn1_uint_decode(struct asn1_ctx *ctx,
 337                                       unsigned char *eoc,
 338                                       unsigned int *integer)
 339 {
 340         unsigned char ch;
 341         unsigned int  len;
 342
 343         if (!asn1_octet_decode(ctx, &ch))
 344                 return 0;
 345
 346         *integer = ch;
 347         if (ch == 0) len = 0;
 348         else len = 1;
 349
 350         while (ctx->pointer < eoc) {
 351                 if (++len > sizeof (unsigned int)) {
 352                         ctx->error = ASN1_ERR_DEC_BADVALUE;
 353                         return 0;
 354                 }
 355
 356                 if (!asn1_octet_decode(ctx, &ch))
 357                         return 0;
 358
 359                 *integer <<= 8;
 360                 *integer |= ch;
 361         }
 362         return 1;
 363 }
 364
 365 static unsigned char asn1_ulong_decode(struct asn1_ctx *ctx,
 366                                        unsigned char *eoc,
 367                                        unsigned long *integer)
 368 {
 369         unsigned char ch;
 370         unsigned int  len;
 371
 372         if (!asn1_octet_decode(ctx, &ch))
 373                 return 0;
 374
 375         *integer = ch;
 376         if (ch == 0) len = 0;
 377         else len = 1;
 378
 379         while (ctx->pointer < eoc) {
 380                 if (++len > sizeof (unsigned long)) {
 381                         ctx->error = ASN1_ERR_DEC_BADVALUE;
 382                         return 0;
 383                 }
 384
 385                 if (!asn1_octet_decode(ctx, &ch))
 386                         return 0;
 387
 388                 *integer <<= 8;
 389                 *integer |= ch;
 390         }
 391         return 1;
 392 }
 393
 394 static unsigned char asn1_octets_decode(struct asn1_ctx *ctx,
 395                                         unsigned char *eoc,
 396                                         unsigned char **octets,
 397                                         unsigned int *len)
 398 {
 399         unsigned char *ptr;
 400
 401         *len = 0;
 402
 403         *octets = kmalloc(eoc - ctx->pointer, GFP_ATOMIC);
 404         if (*octets == NULL)
 405                 return 0;
 406
 407         ptr = *octets;
 408         while (ctx->pointer < eoc) {
 409                 if (!asn1_octet_decode(ctx, ptr++)) {
 410                         kfree(*octets);
 411                         *octets = NULL;
 412                         return 0;
 413                 }
 414                 (*len)++;
 415         }
 416         return 1;
 417 }
 418
 419 static unsigned char asn1_subid_decode(struct asn1_ctx *ctx,
 420                                        unsigned long *subid)
 421 {
 422         unsigned char ch;
 423
 424         *subid = 0;
 425
 426         do {
 427                 if (!asn1_octet_decode(ctx, &ch))
 428                         return 0;
 429
 430                 *subid <<= 7;
 431                 *subid |= ch & 0x7F;
 432         } while ((ch & 0x80) == 0x80);
 433         return 1;
 434 }
 435
 436 static unsigned char asn1_oid_decode(struct asn1_ctx *ctx,
 437                                      unsigned char *eoc,
 438                                      unsigned long **oid,
 439                                      unsigned int *len)
 440 {
 441         unsigned long subid;
 442         unsigned long *optr;
 443         size_t size;
 444
 445         size = eoc - ctx->pointer + 1;
 446
 447         /* first subid actually encodes first two subids */
 448         if (size < 2 || size > ULONG_MAX/sizeof(unsigned long))
 449                 return 0;
 450
 451         *oid = kmalloc(size * sizeof(unsigned long), GFP_ATOMIC);
 452         if (*oid == NULL)
 453                 return 0;
 454
 455         optr = *oid;
 456
 457         if (!asn1_subid_decode(ctx, &subid)) {
 458                 kfree(*oid);
 459                 *oid = NULL;
 460                 return 0;
 461         }
 462
 463         if (subid < 40) {
 464                 optr[0] = 0;
 465                 optr[1] = subid;
 466         } else if (subid < 80) {
 467                 optr[0] = 1;
 468                 optr[1] = subid - 40;
 469         } else {
 470                 optr[0] = 2;
 471                 optr[1] = subid - 80;
 472         }
 473
 474         *len = 2;
 475         optr += 2;
 476
 477         while (ctx->pointer < eoc) {
 478                 if (++(*len) > size) {
 479                         ctx->error = ASN1_ERR_DEC_BADVALUE;
 480                         kfree(*oid);
 481                         *oid = NULL;
 482                         return 0;
 483                 }
 484
 485                 if (!asn1_subid_decode(ctx, optr++)) {
 486                         kfree(*oid);
 487                         *oid = NULL;
 488                         return 0;
 489                 }
 490         }
 491         return 1;
 492 }
 493
 494 /*****************************************************************************
 495  *
 496  * SNMP decoding routines (gxsnmp author Dirk Wisse)
 497  *
 498  *****************************************************************************/
 499
 500 /* SNMP Versions */
 501 #define SNMP_V1                         0
 502 #define SNMP_V2C                        1
 503 #define SNMP_V2                         2
 504 #define SNMP_V3                         3
 505
 506 /* Default Sizes */
 507 #define SNMP_SIZE_COMM                  256
 508 #define SNMP_SIZE_OBJECTID              128
 509 #define SNMP_SIZE_BUFCHR                256
 510 #define SNMP_SIZE_BUFINT                128
 511 #define SNMP_SIZE_SMALLOBJECTID         16
 512
 513 /* Requests */
 514 #define SNMP_PDU_GET                    0
 515 #define SNMP_PDU_NEXT                   1
 516 #define SNMP_PDU_RESPONSE               2
 517 #define SNMP_PDU_SET                    3
 518 #define SNMP_PDU_TRAP1                  4
 519 #define SNMP_PDU_BULK                   5
 520 #define SNMP_PDU_INFORM                 6
 521 #define SNMP_PDU_TRAP2                  7
 522
 523 /* Errors */
 524 #define SNMP_NOERROR                    0
 525 #define SNMP_TOOBIG                     1
 526 #define SNMP_NOSUCHNAME                 2
 527 #define SNMP_BADVALUE                   3
 528 #define SNMP_READONLY                   4
 529 #define SNMP_GENERROR                   5
 530 #define SNMP_NOACCESS                   6
 531 #define SNMP_WRONGTYPE                  7
 532 #define SNMP_WRONGLENGTH                8
 533 #define SNMP_WRONGENCODING              9
 534 #define SNMP_WRONGVALUE                 10
 535 #define SNMP_NOCREATION                 11
 536 #define SNMP_INCONSISTENTVALUE          12
 537 #define SNMP_RESOURCEUNAVAILABLE        13
 538 #define SNMP_COMMITFAILED               14
 539 #define SNMP_UNDOFAILED                 15
 540 #define SNMP_AUTHORIZATIONERROR         16
 541 #define SNMP_NOTWRITABLE                17
 542 #define SNMP_INCONSISTENTNAME           18
 543
 544 /* General SNMP V1 Traps */
 545 #define SNMP_TRAP_COLDSTART             0
 546 #define SNMP_TRAP_WARMSTART             1
 547 #define SNMP_TRAP_LINKDOWN              2
 548 #define SNMP_TRAP_LINKUP                3
 549 #define SNMP_TRAP_AUTFAILURE            4
 550 #define SNMP_TRAP_EQPNEIGHBORLOSS       5
 551 #define SNMP_TRAP_ENTSPECIFIC           6
 552
 553 /* SNMPv1 Types */
 554 #define SNMP_NULL                0
 555 #define SNMP_INTEGER             1    /* l  */
 556 #define SNMP_OCTETSTR            2    /* c  */
 557 #define SNMP_DISPLAYSTR          2    /* c  */
 558 #define SNMP_OBJECTID            3    /* ul */
 559 #define SNMP_IPADDR              4    /* uc */
 560 #define SNMP_COUNTER             5    /* ul */
 561 #define SNMP_GAUGE               6    /* ul */
 562 #define SNMP_TIMETICKS           7    /* ul */
 563 #define SNMP_OPAQUE              8    /* c  */
 564
 565 /* Additional SNMPv2 Types */
 566 #define SNMP_UINTEGER            5    /* ul */
 567 #define SNMP_BITSTR              9    /* uc */
 568 #define SNMP_NSAP               10    /* uc */
 569 #define SNMP_COUNTER64          11    /* ul */
 570 #define SNMP_NOSUCHOBJECT       12
 571 #define SNMP_NOSUCHINSTANCE     13
 572 #define SNMP_ENDOFMIBVIEW       14
 573
 574 union snmp_syntax
 575 {
 576         unsigned char uc[0];    /* 8 bit unsigned */
 577         char c[0];              /* 8 bit signed */
 578         unsigned long ul[0];    /* 32 bit unsigned */
 579         long l[0];              /* 32 bit signed */
 580 };
 581
 582 struct snmp_object
 583 {
 584         unsigned long *id;
 585         unsigned int id_len;
 586         unsigned short type;
 587         unsigned int syntax_len;
 588         union snmp_syntax syntax;
 589 };
 590
 591 struct snmp_request
 592 {
 593         unsigned long id;
 594         unsigned int error_status;
 595         unsigned int error_index;
 596 };
 597
 598 struct snmp_v1_trap
 599 {
 600         unsigned long *id;
 601         unsigned int id_len;
 602         unsigned long ip_address;       /* pointer  */
 603         unsigned int general;
 604         unsigned int specific;
 605         unsigned long time;
 606 };
 607
 608 /* SNMP types */
 609 #define SNMP_IPA    0
 610 #define SNMP_CNT    1
 611 #define SNMP_GGE    2
 612 #define SNMP_TIT    3
 613 #define SNMP_OPQ    4
 614 #define SNMP_C64    6
 615
 616 /* SNMP errors */
 617 #define SERR_NSO    0
 618 #define SERR_NSI    1
 619 #define SERR_EOM    2
 620
 621 static inline void mangle_address(unsigned char *begin,
 622                                   unsigned char *addr,
 623                                   const struct oct1_map *map,
 624                                   __sum16 *check);
 625 struct snmp_cnv
 626 {
 627         unsigned int class;
 628         unsigned int tag;
 629         int syntax;
 630 };
 631
 632 static const struct snmp_cnv snmp_conv[] = {
 633         {ASN1_UNI, ASN1_NUL, SNMP_NULL},
 634         {ASN1_UNI, ASN1_INT, SNMP_INTEGER},
 635         {ASN1_UNI, ASN1_OTS, SNMP_OCTETSTR},
 636         {ASN1_UNI, ASN1_OTS, SNMP_DISPLAYSTR},
 637         {ASN1_UNI, ASN1_OJI, SNMP_OBJECTID},
 638         {ASN1_APL, SNMP_IPA, SNMP_IPADDR},
 639         {ASN1_APL, SNMP_CNT, SNMP_COUNTER},     /* Counter32 */
 640         {ASN1_APL, SNMP_GGE, SNMP_GAUGE},       /* Gauge32 == Unsigned32  */
 641         {ASN1_APL, SNMP_TIT, SNMP_TIMETICKS},
 642         {ASN1_APL, SNMP_OPQ, SNMP_OPAQUE},
 643
 644         /* SNMPv2 data types and errors */
 645         {ASN1_UNI, ASN1_BTS, SNMP_BITSTR},
 646         {ASN1_APL, SNMP_C64, SNMP_COUNTER64},
 647         {ASN1_CTX, SERR_NSO, SNMP_NOSUCHOBJECT},
 648         {ASN1_CTX, SERR_NSI, SNMP_NOSUCHINSTANCE},
 649         {ASN1_CTX, SERR_EOM, SNMP_ENDOFMIBVIEW},
 650         {0,       0,       -1}
 651 };
 652
 653 static unsigned char snmp_tag_cls2syntax(unsigned int tag,
 654                                          unsigned int cls,
 655                                          unsigned short *syntax)
 656 {
 657         const struct snmp_cnv *cnv;
 658
 659         cnv = snmp_conv;
 660
 661         while (cnv->syntax != -1) {
 662                 if (cnv->tag == tag && cnv->class == cls) {
 663                         *syntax = cnv->syntax;
 664                         return 1;
 665                 }
 666                 cnv++;
 667         }
 668         return 0;
 669 }
 670
 671 static unsigned char snmp_object_decode(struct asn1_ctx *ctx,
 672                                         struct snmp_object **obj)
 673 {
 674         unsigned int cls, con, tag, len, idlen;
 675         unsigned short type;
 676         unsigned char *eoc, *end, *p;
 677         unsigned long *lp, *id;
 678         unsigned long ul;
 679         long l;
 680
 681         *obj = NULL;
 682         id = NULL;
 683
 684         if (!asn1_header_decode(ctx, &eoc, &cls, &con, &tag))
 685                 return 0;
 686
 687         if (cls != ASN1_UNI || con != ASN1_CON || tag != ASN1_SEQ)
 688                 return 0;
 689
 690         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 691                 return 0;
 692
 693         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_OJI)
 694                 return 0;
 695
 696         if (!asn1_oid_decode(ctx, end, &id, &idlen))
 697                 return 0;
 698
 699         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag)) {
 700                 kfree(id);
 701                 return 0;
 702         }
 703
 704         if (con != ASN1_PRI) {
 705                 kfree(id);
 706                 return 0;
 707         }
 708
 709         type = 0;
 710         if (!snmp_tag_cls2syntax(tag, cls, &type)) {
 711                 kfree(id);
 712                 return 0;
 713         }
 714
 715         l = 0;
 716         switch (type) {
 717         case SNMP_INTEGER:
 718                 len = sizeof(long);
 719                 if (!asn1_long_decode(ctx, end, &l)) {
 720                         kfree(id);
 721                         return 0;
 722                 }
 723                 *obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
 724                 if (*obj == NULL) {
 725                         kfree(id);
 726                         return 0;
 727                 }
 728                 (*obj)->syntax.l[0] = l;
 729                 break;
 730         case SNMP_OCTETSTR:
 731         case SNMP_OPAQUE:
 732                 if (!asn1_octets_decode(ctx, end, &p, &len)) {
 733                         kfree(id);
 734                         return 0;
 735                 }
 736                 *obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
 737                 if (*obj == NULL) {
 738                         kfree(p);
 739                         kfree(id);
 740                         return 0;
 741                 }
 742                 memcpy((*obj)->syntax.c, p, len);
 743                 kfree(p);
 744                 break;
 745         case SNMP_NULL:
 746         case SNMP_NOSUCHOBJECT:
 747         case SNMP_NOSUCHINSTANCE:
 748         case SNMP_ENDOFMIBVIEW:
 749                 len = 0;
 750                 *obj = kmalloc(sizeof(struct snmp_object), GFP_ATOMIC);
 751                 if (*obj == NULL) {
 752                         kfree(id);
 753                         return 0;
 754                 }
 755                 if (!asn1_null_decode(ctx, end)) {
 756                         kfree(id);
 757                         kfree(*obj);
 758                         *obj = NULL;
 759                         return 0;
 760                 }
 761                 break;
 762         case SNMP_OBJECTID:
 763                 if (!asn1_oid_decode(ctx, end, &lp, &len)) {
 764                         kfree(id);
 765                         return 0;
 766                 }
 767                 len *= sizeof(unsigned long);
 768                 *obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
 769                 if (*obj == NULL) {
 770                         kfree(lp);
 771                         kfree(id);
 772                         return 0;
 773                 }
 774                 memcpy((*obj)->syntax.ul, lp, len);
 775                 kfree(lp);
 776                 break;
 777         case SNMP_IPADDR:
 778                 if (!asn1_octets_decode(ctx, end, &p, &len)) {
 779                         kfree(id);
 780                         return 0;
 781                 }
 782                 if (len != 4) {
 783                         kfree(p);
 784                         kfree(id);
 785                         return 0;
 786                 }
 787                 *obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
 788                 if (*obj == NULL) {
 789                         kfree(p);
 790                         kfree(id);
 791                         return 0;
 792                 }
 793                 memcpy((*obj)->syntax.uc, p, len);
 794                 kfree(p);
 795                 break;
 796         case SNMP_COUNTER:
 797         case SNMP_GAUGE:
 798         case SNMP_TIMETICKS:
 799                 len = sizeof(unsigned long);
 800                 if (!asn1_ulong_decode(ctx, end, &ul)) {
 801                         kfree(id);
 802                         return 0;
 803                 }
 804                 *obj = kmalloc(sizeof(struct snmp_object) + len, GFP_ATOMIC);
 805                 if (*obj == NULL) {
 806                         kfree(id);
 807                         return 0;
 808                 }
 809                 (*obj)->syntax.ul[0] = ul;
 810                 break;
 811         default:
 812                 kfree(id);
 813                 return 0;
 814         }
 815
 816         (*obj)->syntax_len = len;
 817         (*obj)->type = type;
 818         (*obj)->id = id;
 819         (*obj)->id_len = idlen;
 820
 821         if (!asn1_eoc_decode(ctx, eoc)) {
 822                 kfree(id);
 823                 kfree(*obj);
 824                 *obj = NULL;
 825                 return 0;
 826         }
 827         return 1;
 828 }
 829
 830 static unsigned char snmp_request_decode(struct asn1_ctx *ctx,
 831                                          struct snmp_request *request)
 832 {
 833         unsigned int cls, con, tag;
 834         unsigned char *end;
 835
 836         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 837                 return 0;
 838
 839         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
 840                 return 0;
 841
 842         if (!asn1_ulong_decode(ctx, end, &request->id))
 843                 return 0;
 844
 845         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 846                 return 0;
 847
 848         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
 849                 return 0;
 850
 851         if (!asn1_uint_decode(ctx, end, &request->error_status))
 852                 return 0;
 853
 854         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 855                 return 0;
 856
 857         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
 858                 return 0;
 859
 860         if (!asn1_uint_decode(ctx, end, &request->error_index))
 861                 return 0;
 862
 863         return 1;
 864 }
 865
 866 /*
 867  * Fast checksum update for possibly oddly-aligned UDP byte, from the
 868  * code example in the draft.
 869  */
 870 static void fast_csum(__sum16 *csum,
 871                       const unsigned char *optr,
 872                       const unsigned char *nptr,
 873                       int offset)
 874 {
 875         unsigned char s[4];
 876
 877         if (offset & 1) {
 878                 s[0] = ~0;
 879                 s[1] = ~*optr;
 880                 s[2] = 0;
 881                 s[3] = *nptr;
 882         } else {
 883                 s[0] = ~*optr;
 884                 s[1] = ~0;
 885                 s[2] = *nptr;
 886                 s[3] = 0;
 887         }
 888
 889         *csum = csum_fold(csum_partial(s, 4, ~csum_unfold(*csum)));
 890 }
 891
 892 /*
 893  * Mangle IP address.
 894  *      - begin points to the start of the snmp messgae
 895  *      - addr points to the start of the address
 896  */
 897 static inline void mangle_address(unsigned char *begin,
 898                                   unsigned char *addr,
 899                                   const struct oct1_map *map,
 900                                   __sum16 *check)
 901 {
 902         if (map->from == NOCT1(addr)) {
 903                 u_int32_t old;
 904
 905                 if (debug)
 906                         memcpy(&old, addr, sizeof(old));
 907
 908                 *addr = map->to;
 909
 910                 /* Update UDP checksum if being used */
 911                 if (*check) {
 912                         fast_csum(check,
 913                                   &map->from, &map->to, addr - begin);
 914
 915                 }
 916
 917                 if (debug)
 918                         printk(KERN_DEBUG "bsalg: mapped %pI4 to %pI4\n",
 919                                &old, addr);
 920         }
 921 }
 922
 923 static unsigned char snmp_trap_decode(struct asn1_ctx *ctx,
 924                                       struct snmp_v1_trap *trap,
 925                                       const struct oct1_map *map,
 926                                       __sum16 *check)
 927 {
 928         unsigned int cls, con, tag, len;
 929         unsigned char *end;
 930
 931         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 932                 return 0;
 933
 934         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_OJI)
 935                 return 0;
 936
 937         if (!asn1_oid_decode(ctx, end, &trap->id, &trap->id_len))
 938                 return 0;
 939
 940         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 941                 goto err_id_free;
 942
 943         if (!((cls == ASN1_APL && con == ASN1_PRI && tag == SNMP_IPA) ||
 944               (cls == ASN1_UNI && con == ASN1_PRI && tag == ASN1_OTS)))
 945                 goto err_id_free;
 946
 947         if (!asn1_octets_decode(ctx, end, (unsigned char **)&trap->ip_address, &len))
 948                 goto err_id_free;
 949
 950         /* IPv4 only */
 951         if (len != 4)
 952                 goto err_addr_free;
 953
 954         mangle_address(ctx->begin, ctx->pointer - 4, map, check);
 955
 956         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 957                 goto err_addr_free;
 958
 959         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
 960                 goto err_addr_free;
 961
 962         if (!asn1_uint_decode(ctx, end, &trap->general))
 963                 goto err_addr_free;
 964
 965         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 966                 goto err_addr_free;
 967
 968         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
 969                 goto err_addr_free;
 970
 971         if (!asn1_uint_decode(ctx, end, &trap->specific))
 972                 goto err_addr_free;
 973
 974         if (!asn1_header_decode(ctx, &end, &cls, &con, &tag))
 975                 goto err_addr_free;
 976
 977         if (!((cls == ASN1_APL && con == ASN1_PRI && tag == SNMP_TIT) ||
 978               (cls == ASN1_UNI && con == ASN1_PRI && tag == ASN1_INT)))
 979                 goto err_addr_free;
 980
 981         if (!asn1_ulong_decode(ctx, end, &trap->time))
 982                 goto err_addr_free;
 983
 984         return 1;
 985
 986 err_addr_free:
 987         kfree((unsigned long *)trap->ip_address);
 988
 989 err_id_free:
 990         kfree(trap->id);
 991
 992         return 0;
 993 }
 994
 995 /*****************************************************************************
 996  *
 997  * Misc. routines
 998  *
 999  *****************************************************************************/
1000
1001 /*
1002  * Parse and mangle SNMP message according to mapping.
1003  * (And this is the fucking 'basic' method).
1004  */
1005 static int snmp_parse_mangle(unsigned char *msg,
1006                              u_int16_t len,
1007                              const struct oct1_map *map,
1008                              __sum16 *check)
1009 {
1010         unsigned char *eoc, *end;
1011         unsigned int cls, con, tag, vers, pdutype;
1012         struct asn1_ctx ctx;
1013         struct asn1_octstr comm;
1014         struct snmp_object *obj;
1015
1016         if (debug > 1)
1017                 print_hex_dump(KERN_DEBUG, "", DUMP_PREFIX_NONE, 16, 1,
1018                                msg, len, 0);
1019
1020         asn1_open(&ctx, msg, len);
1021
1022         /*
1023          * Start of SNMP message.
1024          */
1025         if (!asn1_header_decode(&ctx, &eoc, &cls, &con, &tag))
1026                 return 0;
1027         if (cls != ASN1_UNI || con != ASN1_CON || tag != ASN1_SEQ)
1028                 return 0;
1029
1030         /*
1031          * Version 1 or 2 handled.
1032          */
1033         if (!asn1_header_decode(&ctx, &end, &cls, &con, &tag))
1034                 return 0;
1035         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_INT)
1036                 return 0;
1037         if (!asn1_uint_decode (&ctx, end, &vers))
1038                 return 0;
1039         if (debug > 1)
1040                 pr_debug("bsalg: snmp version: %u\n", vers + 1);
1041         if (vers > 1)
1042                 return 1;
1043
1044         /*
1045          * Community.
1046          */
1047         if (!asn1_header_decode (&ctx, &end, &cls, &con, &tag))
1048                 return 0;
1049         if (cls != ASN1_UNI || con != ASN1_PRI || tag != ASN1_OTS)
1050                 return 0;
1051         if (!asn1_octets_decode(&ctx, end, &comm.data, &comm.len))
1052                 return 0;
1053         if (debug > 1) {
1054                 unsigned int i;
1055
1056                 pr_debug("bsalg: community: ");
1057                 for (i = 0; i < comm.len; i++)
1058                         pr_cont("%c", comm.data[i]);
1059                 pr_cont("\n");
1060         }
1061         kfree(comm.data);
1062
1063         /*
1064          * PDU type
1065          */
1066         if (!asn1_header_decode(&ctx, &eoc, &cls, &con, &pdutype))
1067                 return 0;
1068         if (cls != ASN1_CTX || con != ASN1_CON)
1069                 return 0;
1070         if (debug > 1) {
1071                 static const unsigned char *const pdus[] = {
1072                         [SNMP_PDU_GET] = "get",
1073                         [SNMP_PDU_NEXT] = "get-next",
1074                         [SNMP_PDU_RESPONSE] = "response",
1075                         [SNMP_PDU_SET] = "set",
1076                         [SNMP_PDU_TRAP1] = "trapv1",
1077                         [SNMP_PDU_BULK] = "bulk",
1078                         [SNMP_PDU_INFORM] = "inform",
1079                         [SNMP_PDU_TRAP2] = "trapv2"
1080                 };
1081
1082                 if (pdutype > SNMP_PDU_TRAP2)
1083                         pr_debug("bsalg: bad pdu type %u\n", pdutype);
1084                 else
1085                         pr_debug("bsalg: pdu: %s\n", pdus[pdutype]);
1086         }
1087         if (pdutype != SNMP_PDU_RESPONSE &&
1088             pdutype != SNMP_PDU_TRAP1 && pdutype != SNMP_PDU_TRAP2)
1089                 return 1;
1090
1091         /*
1092          * Request header or v1 trap
1093          */
1094         if (pdutype == SNMP_PDU_TRAP1) {
1095                 struct snmp_v1_trap trap;
1096                 unsigned char ret = snmp_trap_decode(&ctx, &trap, map, check);
1097
1098                 if (ret) {
1099                         kfree(trap.id);
1100                         kfree((unsigned long *)trap.ip_address);
1101                 } else
1102                         return ret;
1103
1104         } else {
1105                 struct snmp_request req;
1106
1107                 if (!snmp_request_decode(&ctx, &req))
1108                         return 0;
1109
1110                 if (debug > 1)
1111                         pr_debug("bsalg: request: id=0x%lx error_status=%u "
1112                         "error_index=%u\n", req.id, req.error_status,
1113                         req.error_index);
1114         }
1115
1116         /*
1117          * Loop through objects, look for IP addresses to mangle.
1118          */
1119         if (!asn1_header_decode(&ctx, &eoc, &cls, &con, &tag))
1120                 return 0;
1121
1122         if (cls != ASN1_UNI || con != ASN1_CON || tag != ASN1_SEQ)
1123                 return 0;
1124
1125         while (!asn1_eoc_decode(&ctx, eoc)) {
1126                 unsigned int i;
1127
1128                 if (!snmp_object_decode(&ctx, &obj)) {
1129                         if (obj) {
1130                                 kfree(obj->id);
1131                                 kfree(obj);
1132                         }
1133                         return 0;
1134                 }
1135
1136                 if (debug > 1) {
1137                         pr_debug("bsalg: object: ");
1138                         for (i = 0; i < obj->id_len; i++) {
1139                                 if (i > 0)
1140                                         pr_cont(".");
1141                                 pr_cont("%lu", obj->id[i]);
1142                         }
1143                         pr_cont(": type=%u\n", obj->type);
1144
1145                 }
1146
1147                 if (obj->type == SNMP_IPADDR)
1148                         mangle_address(ctx.begin, ctx.pointer - 4, map, check);
1149
1150                 kfree(obj->id);
1151                 kfree(obj);
1152         }
1153
1154         if (!asn1_eoc_decode(&ctx, eoc))
1155                 return 0;
1156
1157         return 1;
1158 }
1159
1160 /*****************************************************************************
1161  *
1162  * NAT routines.
1163  *
1164  *****************************************************************************/
1165
1166 /*
1167  * SNMP translation routine.
1168  */
1169 static int snmp_translate(struct nf_conn *ct,
1170                           enum ip_conntrack_info ctinfo,
1171                           struct sk_buff *skb)
1172 {
1173         struct iphdr *iph = ip_hdr(skb);
1174         struct udphdr *udph = (struct udphdr *)((__be32 *)iph + iph->ihl);
1175         u_int16_t udplen = ntohs(udph->len);
1176         u_int16_t paylen = udplen - sizeof(struct udphdr);
1177         int dir = CTINFO2DIR(ctinfo);
1178         struct oct1_map map;
1179
1180         /*
1181          * Determine mappping for application layer addresses based
1182          * on NAT manipulations for the packet.
1183          */
1184         if (dir == IP_CT_DIR_ORIGINAL) {
1185                 /* SNAT traps */
1186                 map.from = NOCT1(&ct->tuplehash[dir].tuple.src.u3.ip);
1187                 map.to = NOCT1(&ct->tuplehash[!dir].tuple.dst.u3.ip);
1188         } else {
1189                 /* DNAT replies */
1190                 map.from = NOCT1(&ct->tuplehash[!dir].tuple.src.u3.ip);
1191                 map.to = NOCT1(&ct->tuplehash[dir].tuple.dst.u3.ip);
1192         }
1193
1194         if (map.from == map.to)
1195                 return NF_ACCEPT;
1196
1197         if (!snmp_parse_mangle((unsigned char *)udph + sizeof(struct udphdr),
1198                                paylen, &map, &udph->check)) {
1199                 net_warn_ratelimited("bsalg: parser failed\n");
1200                 return NF_DROP;
1201         }
1202         return NF_ACCEPT;
1203 }
1204
1205 /* We don't actually set up expectations, just adjust internal IP
1206  * addresses if this is being NATted */
1207 static int help(struct sk_buff *skb, unsigned int protoff,
1208                 struct nf_conn *ct,
1209                 enum ip_conntrack_info ctinfo)
1210 {
1211         int dir = CTINFO2DIR(ctinfo);
1212         unsigned int ret;
1213         const struct iphdr *iph = ip_hdr(skb);
1214         const struct udphdr *udph = (struct udphdr *)((__be32 *)iph + iph->ihl);
1215
1216         /* SNMP replies and originating SNMP traps get mangled */
1217         if (udph->source == htons(SNMP_PORT) && dir != IP_CT_DIR_REPLY)
1218                 return NF_ACCEPT;
1219         if (udph->dest == htons(SNMP_TRAP_PORT) && dir != IP_CT_DIR_ORIGINAL)
1220                 return NF_ACCEPT;
1221
1222         /* No NAT? */
1223         if (!(ct->status & IPS_NAT_MASK))
1224                 return NF_ACCEPT;
1225
1226         /*
1227          * Make sure the packet length is ok.  So far, we were only guaranteed
1228          * to have a valid length IP header plus 8 bytes, which means we have
1229          * enough room for a UDP header.  Just verify the UDP length field so we
1230          * can mess around with the payload.
1231          */
1232         if (ntohs(udph->len) != skb->len - (iph->ihl << 2)) {
1233                 net_warn_ratelimited("SNMP: dropping malformed packet src=%pI4 dst=%pI4\n",
1234                                      &iph->saddr, &iph->daddr);
1235                  return NF_DROP;
1236         }
1237
1238         if (!skb_make_writable(skb, skb->len))
1239                 return NF_DROP;
1240
1241         spin_lock_bh(&snmp_lock);
1242         ret = snmp_translate(ct, ctinfo, skb);
1243         spin_unlock_bh(&snmp_lock);
1244         return ret;
1245 }
1246
1247 static const struct nf_conntrack_expect_policy snmp_exp_policy = {
1248         .max_expected   = 0,
1249         .timeout        = 180,
1250 };
1251
1252 static struct nf_conntrack_helper snmp_trap_helper __read_mostly = {
1253         .me                     = THIS_MODULE,
1254         .help                   = help,
1255         .expect_policy          = &snmp_exp_policy,
1256         .name                   = "snmp_trap",
1257         .tuple.src.l3num        = AF_INET,
1258         .tuple.src.u.udp.port   = cpu_to_be16(SNMP_TRAP_PORT),
1259         .tuple.dst.protonum     = IPPROTO_UDP,
1260 };
1261
1262 /*****************************************************************************
1263  *
1264  * Module stuff.
1265  *
1266  *****************************************************************************/
1267
1268 static int __init nf_nat_snmp_basic_init(void)
1269 {
1270         BUG_ON(nf_nat_snmp_hook != NULL);
1271         RCU_INIT_POINTER(nf_nat_snmp_hook, help);
1272
1273         return nf_conntrack_helper_register(&snmp_trap_helper);
1274 }
1275
1276 static void __exit nf_nat_snmp_basic_fini(void)
1277 {
1278         RCU_INIT_POINTER(nf_nat_snmp_hook, NULL);
1279         synchronize_rcu();
1280         nf_conntrack_helper_unregister(&snmp_trap_helper);
1281 }
1282
1283 module_init(nf_nat_snmp_basic_init);
1284 module_exit(nf_nat_snmp_basic_fini);
1285
1286 module_param(debug, int, 0600);