src/bpf.c

   1 /*
   2  * netsniff-ng - the packet sniffing beast
   3  * By Daniel Borkmann <daniel@netsniff-ng.org>
   4  * Copyright 2009, 2010 Daniel Borkmann.
   5  * Copyright 2009, 2010 Emmanuel Roullit.
   6  * Copyright 1990-1996 The Regents of the University of
   7  * California. All rights reserved. (3-clause BSD license)
   8  * Subject to the GPL, version 2.
   9  */
  10
  11 #include <stdint.h>
  12 #include <stdio.h>
  13 #include <arpa/inet.h>
  14 #include <sys/types.h>
  15 #include <sys/stat.h>
  16 #include <fcntl.h>
  17
  18 #include "bpf.h"
  19 #include "xmalloc.h"
  20 #include "xstring.h"
  21 #include "die.h"
  22
  23 /* This is a bug in libpcap, they actually use 'unsigned long' instead
  24  * of short! */
  25 #define EXTRACT_SHORT(packet)                                           \
  26                 ((unsigned short) ntohs(*(unsigned short *) packet))
  27 #define EXTRACT_LONG(packet)                                            \
  28                 (ntohl(*(unsigned long *) packet))
  29 #ifndef BPF_MEMWORDS
  30 # define BPF_MEMWORDS 16
  31 #endif
  32
  33 static char *bpf_dump(const struct sock_filter bpf, int n)
  34 {
  35         int v;
  36         const char *fmt, *op;
  37         static char image[256];
  38         char operand[64];
  39
  40         v = bpf.k;
  41         switch (bpf.code) {
  42         default:
  43                 op = "unimp";
  44                 fmt = "0x%x";
  45                 v = bpf.code;
  46                 break;
  47         case BPF_RET | BPF_K:
  48                 op = "ret";
  49                 fmt = "#0x%x";
  50                 break;
  51         case BPF_RET | BPF_A:
  52                 op = "ret";
  53                 fmt = "";
  54                 break;
  55         case BPF_LD | BPF_W | BPF_ABS:
  56                 op = "ld";
  57                 fmt = "[%d]";
  58                 break;
  59         case BPF_LD | BPF_H | BPF_ABS:
  60                 op = "ldh";
  61                 fmt = "[%d]";
  62                 break;
  63         case BPF_LD | BPF_B | BPF_ABS:
  64                 op = "ldb";
  65                 fmt = "[%d]";
  66                 break;
  67         case BPF_LD | BPF_W | BPF_LEN:
  68                 op = "ld";
  69                 fmt = "#pktlen";
  70                 break;
  71         case BPF_LD | BPF_W | BPF_IND:
  72                 op = "ld";
  73                 fmt = "[x + %d]";
  74                 break;
  75         case BPF_LD | BPF_H | BPF_IND:
  76                 op = "ldh";
  77                 fmt = "[x + %d]";
  78                 break;
  79         case BPF_LD | BPF_B | BPF_IND:
  80                 op = "ldb";
  81                 fmt = "[x + %d]";
  82                 break;
  83         case BPF_LD | BPF_IMM:
  84                 op = "ld";
  85                 fmt = "#0x%x";
  86                 break;
  87         case BPF_LDX | BPF_IMM:
  88                 op = "ldx";
  89                 fmt = "#0x%x";
  90                 break;
  91         case BPF_LDX | BPF_MSH | BPF_B:
  92                 op = "ldxb";
  93                 fmt = "4*([%d]&0xf)";
  94                 break;
  95         case BPF_LD | BPF_MEM:
  96                 op = "ld";
  97                 fmt = "M[%d]";
  98                 break;
  99         case BPF_LDX | BPF_MEM:
 100                 op = "ldx";
 101                 fmt = "M[%d]";
 102                 break;
 103         case BPF_ST:
 104                 op = "st";
 105                 fmt = "M[%d]";
 106                 break;
 107         case BPF_STX:
 108                 op = "stx";
 109                 fmt = "M[%d]";
 110                 break;
 111         case BPF_JMP | BPF_JA:
 112                 op = "ja";
 113                 fmt = "%d";
 114                 v = n + 1 + bpf.k;
 115                 break;
 116         case BPF_JMP | BPF_JGT | BPF_K:
 117                 op = "jgt";
 118                 fmt = "#0x%x";
 119                 break;
 120         case BPF_JMP | BPF_JGE | BPF_K:
 121                 op = "jge";
 122                 fmt = "#0x%x";
 123                 break;
 124         case BPF_JMP | BPF_JEQ | BPF_K:
 125                 op = "jeq";
 126                 fmt = "#0x%x";
 127                 break;
 128         case BPF_JMP | BPF_JSET | BPF_K:
 129                 op = "jset";
 130                 fmt = "#0x%x";
 131                 break;
 132         case BPF_JMP | BPF_JGT | BPF_X:
 133                 op = "jgt";
 134                 fmt = "x";
 135                 break;
 136         case BPF_JMP | BPF_JGE | BPF_X:
 137                 op = "jge";
 138                 fmt = "x";
 139                 break;
 140         case BPF_JMP | BPF_JEQ | BPF_X:
 141                 op = "jeq";
 142                 fmt = "x";
 143                 break;
 144         case BPF_JMP | BPF_JSET | BPF_X:
 145                 op = "jset";
 146                 fmt = "x";
 147                 break;
 148         case BPF_ALU | BPF_ADD | BPF_X:
 149                 op = "add";
 150                 fmt = "x";
 151                 break;
 152         case BPF_ALU | BPF_SUB | BPF_X:
 153                 op = "sub";
 154                 fmt = "x";
 155                 break;
 156         case BPF_ALU | BPF_MUL | BPF_X:
 157                 op = "mul";
 158                 fmt = "x";
 159                 break;
 160         case BPF_ALU | BPF_DIV | BPF_X:
 161                 op = "div";
 162                 fmt = "x";
 163                 break;
 164         case BPF_ALU | BPF_AND | BPF_X:
 165                 op = "and";
 166                 fmt = "x";
 167                 break;
 168         case BPF_ALU | BPF_OR | BPF_X:
 169                 op = "or";
 170                 fmt = "x";
 171                 break;
 172         case BPF_ALU | BPF_LSH | BPF_X:
 173                 op = "lsh";
 174                 fmt = "x";
 175                 break;
 176         case BPF_ALU | BPF_RSH | BPF_X:
 177                 op = "rsh";
 178                 fmt = "x";
 179                 break;
 180         case BPF_ALU | BPF_ADD | BPF_K:
 181                 op = "add";
 182                 fmt = "#%d";
 183                 break;
 184         case BPF_ALU | BPF_SUB | BPF_K:
 185                 op = "sub";
 186                 fmt = "#%d";
 187                 break;
 188         case BPF_ALU | BPF_MUL | BPF_K:
 189                 op = "mul";
 190                 fmt = "#%d";
 191                 break;
 192         case BPF_ALU | BPF_DIV | BPF_K:
 193                 op = "div";
 194                 fmt = "#%d";
 195                 break;
 196         case BPF_ALU | BPF_AND | BPF_K:
 197                 op = "and";
 198                 fmt = "#0x%x";
 199                 break;
 200         case BPF_ALU | BPF_OR | BPF_K:
 201                 op = "or";
 202                 fmt = "#0x%x";
 203                 break;
 204         case BPF_ALU | BPF_LSH | BPF_K:
 205                 op = "lsh";
 206                 fmt = "#%d";
 207                 break;
 208         case BPF_ALU | BPF_RSH | BPF_K:
 209                 op = "rsh";
 210                 fmt = "#%d";
 211                 break;
 212         case BPF_ALU | BPF_NEG:
 213                 op = "neg";
 214                 fmt = "";
 215                 break;
 216         case BPF_MISC | BPF_TAX:
 217                 op = "tax";
 218                 fmt = "";
 219                 break;
 220         case BPF_MISC | BPF_TXA:
 221                 op = "txa";
 222                 fmt = "";
 223                 break;
 224         }
 225
 226         slprintf(operand, sizeof(operand), fmt, v);
 227         slprintf(image, sizeof(image),
 228                  (BPF_CLASS(bpf.code) == BPF_JMP &&
 229                   BPF_OP(bpf.code) != BPF_JA) ?
 230                  " L%d: %s %s, L%d, L%d" : " L%d: %s %s",
 231                  n, op, operand, n + 1 + bpf.jt, n + 1 + bpf.jf);
 232
 233         return image;
 234 }
 235
 236 void bpf_dump_all(struct sock_fprog *bpf)
 237 {
 238         int i;
 239         for (i = 0; i < bpf->len; ++i)
 240                 printf("%s\n", bpf_dump(bpf->filter[i], i));
 241 }
 242
 243 void bpf_attach_to_sock(int sock, struct sock_fprog *bpf)
 244 {
 245         if (bpf->len == 1)
 246                 if (bpf->filter[0].code == BPF_RET &&
 247                     bpf->filter[0].k == 0xFFFFFFFF)
 248                         return;
 249
 250         int ret = setsockopt(sock, SOL_SOCKET, SO_ATTACH_FILTER, bpf,
 251                              sizeof(*bpf));
 252         if (ret < 0)
 253                 panic("Cannot attach filter to socket!\n");
 254 }
 255
 256 void bpf_detach_from_sock(int sock)
 257 {
 258         int ret, empty = 0;
 259
 260         ret = setsockopt(sock, SOL_SOCKET, SO_DETACH_FILTER, &empty,
 261                          sizeof(empty));
 262         if (ret < 0)
 263                 panic("Cannot detach filter from socket!\n");
 264 }
 265
 266 void enable_kernel_bpf_jit_compiler(void)
 267 {
 268         int fd;
 269         ssize_t ret;
 270         char *file = "/proc/sys/net/core/bpf_jit_enable";
 271
 272         fd = open(file, O_WRONLY);
 273         if (fd < 0)
 274                 return;
 275
 276         ret = write(fd, "1", strlen("1"));
 277         if (ret > 0)
 278                 printf("BPF JIT\n");
 279
 280         close(fd);
 281 }
 282
 283 int bpf_validate(const struct sock_fprog *bpf)
 284 {
 285         uint32_t i, from;
 286         const struct sock_filter *p;
 287
 288         if (!bpf)
 289                 return 0;
 290         if (bpf->len < 1)
 291                 return 0;
 292
 293         for (i = 0; i < bpf->len; ++i) {
 294                 p = &bpf->filter[i];
 295                 switch (BPF_CLASS(p->code)) {
 296                         /*
 297                          * Check that memory operations use valid addresses.
 298                          */
 299                 case BPF_LD:
 300                 case BPF_LDX:
 301                         switch (BPF_MODE(p->code)) {
 302                         case BPF_IMM:
 303                                 break;
 304                         case BPF_ABS:
 305                         case BPF_IND:
 306                         case BPF_MSH:
 307                                 /*
 308                                  * There's no maximum packet data size
 309                                  * in userland.  The runtime packet length
 310                                  * check suffices.
 311                                  */
 312                                 break;
 313                         case BPF_MEM:
 314                                 if (p->k >= BPF_MEMWORDS)
 315                                         return 0;
 316                                 break;
 317                         case BPF_LEN:
 318                                 break;
 319                         default:
 320                                 return 0;
 321                         }
 322                         break;
 323                 case BPF_ST:
 324                 case BPF_STX:
 325                         if (p->k >= BPF_MEMWORDS)
 326                                 return 0;
 327                         break;
 328                 case BPF_ALU:
 329                         switch (BPF_OP(p->code)) {
 330                         case BPF_ADD:
 331                         case BPF_SUB:
 332                         case BPF_MUL:
 333                         case BPF_OR:
 334                         case BPF_AND:
 335                         case BPF_LSH:
 336                         case BPF_RSH:
 337                         case BPF_NEG:
 338                                 break;
 339                         case BPF_DIV:
 340                                 /*
 341                                  * Check for constant division by 0.
 342                                  */
 343                                 if (BPF_RVAL(p->code) == BPF_K && p->k == 0)
 344                                         return 0;
 345                                 break;
 346                         default:
 347                                 return 0;
 348                         }
 349                         break;
 350                 case BPF_JMP:
 351                         /*
 352                          * Check that jumps are within the code block,
 353                          * and that unconditional branches don't go
 354                          * backwards as a result of an overflow.
 355                          * Unconditional branches have a 32-bit offset,
 356                          * so they could overflow; we check to make
 357                          * sure they don't.  Conditional branches have
 358                          * an 8-bit offset, and the from address is <=
 359                          * BPF_MAXINSNS, and we assume that BPF_MAXINSNS
 360                          * is sufficiently small that adding 255 to it
 361                          * won't overflow.
 362                          *
 363                          * We know that len is <= BPF_MAXINSNS, and we
 364                          * assume that BPF_MAXINSNS is < the maximum size
 365                          * of a u_int, so that i + 1 doesn't overflow.
 366                          *
 367                          * For userland, we don't know that the from
 368                          * or len are <= BPF_MAXINSNS, but we know that
 369                          * from <= len, and, except on a 64-bit system,
 370                          * it's unlikely that len, if it truly reflects
 371                          * the size of the program we've been handed,
 372                          * will be anywhere near the maximum size of
 373                          * a u_int.  We also don't check for backward
 374                          * branches, as we currently support them in
 375                          * userland for the protochain operation.
 376                          */
 377                         from = i + 1;
 378                         switch (BPF_OP(p->code)) {
 379                         case BPF_JA:
 380                                 if (from + p->k >= bpf->len)
 381                                         return 0;
 382                                 break;
 383                         case BPF_JEQ:
 384                         case BPF_JGT:
 385                         case BPF_JGE:
 386                         case BPF_JSET:
 387                                 if (from + p->jt >= bpf->len ||
 388                                     from + p->jf >= bpf->len)
 389                                         return 0;
 390                                 break;
 391                         default:
 392                                 return 0;
 393                         }
 394                         break;
 395                 case BPF_RET:
 396                         break;
 397                 case BPF_MISC:
 398                         break;
 399                 default:
 400                         return 0;
 401                 }
 402         }
 403
 404         return BPF_CLASS(bpf->filter[bpf->len - 1].code) == BPF_RET;
 405 }
 406
 407 uint32_t bpf_run_filter(const struct sock_fprog * fcode, uint8_t * packet,
 408                         size_t plen)
 409 {
 410         /* XXX: caplen == len */
 411         uint32_t A, X;
 412         uint32_t k;
 413         struct sock_filter *bpf;
 414         int32_t mem[BPF_MEMWORDS];
 415
 416         if (fcode == NULL || fcode->filter == NULL || fcode->len == 0)
 417                 return 0xFFFFFFFF;
 418
 419         A = 0;
 420         X = 0;
 421
 422         bpf = fcode->filter;
 423         --bpf;
 424
 425         while (1) {
 426                 ++bpf;
 427
 428                 switch (bpf->code) {
 429                 default:
 430                         return 0;
 431                 case BPF_RET | BPF_K:
 432                         return (uint32_t) bpf->k;
 433                 case BPF_RET | BPF_A:
 434                         return (uint32_t) A;
 435                 case BPF_LD | BPF_W | BPF_ABS:
 436                         k = bpf->k;
 437                         if (k + sizeof(int32_t) > plen)
 438                                 return 0;
 439                         A = EXTRACT_LONG(&packet[k]);
 440                         continue;
 441                 case BPF_LD | BPF_H | BPF_ABS:
 442                         k = bpf->k;
 443                         if (k + sizeof(short) > plen)
 444                                 return 0;
 445                         A = EXTRACT_SHORT(&packet[k]);
 446                         continue;
 447                 case BPF_LD | BPF_B | BPF_ABS:
 448                         k = bpf->k;
 449                         if (k >= plen)
 450                                 return 0;
 451                         A = packet[k];
 452                         continue;
 453                 case BPF_LD | BPF_W | BPF_LEN:
 454                         A = plen;
 455                         continue;
 456                 case BPF_LDX | BPF_W | BPF_LEN:
 457                         X = plen;
 458                         continue;
 459                 case BPF_LD | BPF_W | BPF_IND:
 460                         k = X + bpf->k;
 461                         if (k + sizeof(int32_t) > plen)
 462                                 return 0;
 463                         A = EXTRACT_LONG(&packet[k]);
 464                         continue;
 465                 case BPF_LD | BPF_H | BPF_IND:
 466                         k = X + bpf->k;
 467                         if (k + sizeof(short) > plen)
 468                                 return 0;
 469                         A = EXTRACT_SHORT(&packet[k]);
 470                         continue;
 471                 case BPF_LD | BPF_B | BPF_IND:
 472                         k = X + bpf->k;
 473                         if (k >= plen)
 474                                 return 0;
 475                         A = packet[k];
 476                         continue;
 477                 case BPF_LDX | BPF_MSH | BPF_B:
 478                         k = bpf->k;
 479                         if (k >= plen)
 480                                 return 0;
 481                         X = (packet[bpf->k] & 0xf) << 2;
 482                         continue;
 483                 case BPF_LD | BPF_IMM:
 484                         A = bpf->k;
 485                         continue;
 486                 case BPF_LDX | BPF_IMM:
 487                         X = bpf->k;
 488                         continue;
 489                 case BPF_LD | BPF_MEM:
 490                         A = mem[bpf->k];
 491                         continue;
 492                 case BPF_LDX | BPF_MEM:
 493                         X = mem[bpf->k];
 494                         continue;
 495                 case BPF_ST:
 496                         mem[bpf->k] = A;
 497                         continue;
 498                 case BPF_STX:
 499                         mem[bpf->k] = X;
 500                         continue;
 501                 case BPF_JMP | BPF_JA:
 502                         bpf += bpf->k;
 503                         continue;
 504                 case BPF_JMP | BPF_JGT | BPF_K:
 505                         bpf += (A > bpf->k) ? bpf->jt : bpf->jf;
 506                         continue;
 507                 case BPF_JMP | BPF_JGE | BPF_K:
 508                         bpf += (A >= bpf->k) ? bpf->jt : bpf->jf;
 509                         continue;
 510                 case BPF_JMP | BPF_JEQ | BPF_K:
 511                         bpf += (A == bpf->k) ? bpf->jt : bpf->jf;
 512                         continue;
 513                 case BPF_JMP | BPF_JSET | BPF_K:
 514                         bpf += (A & bpf->k) ? bpf->jt : bpf->jf;
 515                         continue;
 516                 case BPF_JMP | BPF_JGT | BPF_X:
 517                         bpf += (A > X) ? bpf->jt : bpf->jf;
 518                         continue;
 519                 case BPF_JMP | BPF_JGE | BPF_X:
 520                         bpf += (A >= X) ? bpf->jt : bpf->jf;
 521                         continue;
 522                 case BPF_JMP | BPF_JEQ | BPF_X:
 523                         bpf += (A == X) ? bpf->jt : bpf->jf;
 524                         continue;
 525                 case BPF_JMP | BPF_JSET | BPF_X:
 526                         bpf += (A & X) ? bpf->jt : bpf->jf;
 527                         continue;
 528                 case BPF_ALU | BPF_ADD | BPF_X:
 529                         A += X;
 530                         continue;
 531                 case BPF_ALU | BPF_SUB | BPF_X:
 532                         A -= X;
 533                         continue;
 534                 case BPF_ALU | BPF_MUL | BPF_X:
 535                         A *= X;
 536                         continue;
 537                 case BPF_ALU | BPF_DIV | BPF_X:
 538                         if (X == 0)
 539                                 return 0;
 540                         A /= X;
 541                         continue;
 542                 case BPF_ALU | BPF_AND | BPF_X:
 543                         A &= X;
 544                         continue;
 545                 case BPF_ALU | BPF_OR | BPF_X:
 546                         A |= X;
 547                         continue;
 548                 case BPF_ALU | BPF_LSH | BPF_X:
 549                         A <<= X;
 550                         continue;
 551                 case BPF_ALU | BPF_RSH | BPF_X:
 552                         A >>= X;
 553                         continue;
 554                 case BPF_ALU | BPF_ADD | BPF_K:
 555                         A += bpf->k;
 556                         continue;
 557                 case BPF_ALU | BPF_SUB | BPF_K:
 558                         A -= bpf->k;
 559                         continue;
 560                 case BPF_ALU | BPF_MUL | BPF_K:
 561                         A *= bpf->k;
 562                         continue;
 563                 case BPF_ALU | BPF_DIV | BPF_K:
 564                         A /= bpf->k;
 565                         continue;
 566                 case BPF_ALU | BPF_AND | BPF_K:
 567                         A &= bpf->k;
 568                         continue;
 569                 case BPF_ALU | BPF_OR | BPF_K:
 570                         A |= bpf->k;
 571                         continue;
 572                 case BPF_ALU | BPF_LSH | BPF_K:
 573                         A <<= bpf->k;
 574                         continue;
 575                 case BPF_ALU | BPF_RSH | BPF_K:
 576                         A >>= bpf->k;
 577                         continue;
 578                 case BPF_ALU | BPF_NEG:
 579                         A = -A;
 580                         continue;
 581                 case BPF_MISC | BPF_TAX:
 582                         X = A;
 583                         continue;
 584                 case BPF_MISC | BPF_TXA:
 585                         A = X;
 586                         continue;
 587                 }
 588         }
 589 }
 590
 591 void bpf_parse_rules(char *rulefile, struct sock_fprog *bpf)
 592 {
 593         int ret;
 594         char buff[256];
 595         struct sock_filter sf_single = { 0x06, 0, 0, 0xFFFFFFFF };
 596         FILE *fp;
 597
 598         if (rulefile == NULL) {
 599                 bpf->len = 1;
 600                 bpf->filter = xmalloc(sizeof(sf_single));
 601                 fmemcpy(&bpf->filter[0], &sf_single, sizeof(sf_single));
 602                 return;
 603         }
 604
 605         fp = fopen(rulefile, "r");
 606         if (!fp)
 607                 panic("Cannot read BPF rule file!\n");
 608
 609         fmemset(buff, 0, sizeof(buff));
 610         while (fgets(buff, sizeof(buff), fp) != NULL) {
 611                 buff[sizeof(buff) - 1] = 0;
 612                 if (buff[0] != '{') {
 613                         fmemset(buff, 0, sizeof(buff));
 614                         continue;
 615                 }
 616
 617                 fmemset(&sf_single, 0, sizeof(sf_single));
 618                 ret = sscanf(buff, "{ 0x%x, %u, %u, 0x%08x },",
 619                              (unsigned int *) &sf_single.code,
 620                              (unsigned int *) &sf_single.jt,
 621                              (unsigned int *) &sf_single.jf,
 622                              (unsigned int *) &sf_single.k);
 623                 if (ret != 4)
 624                         panic("BPF syntax error!\n");
 625                 bpf->len++;
 626                 bpf->filter = xrealloc(bpf->filter, 1,
 627                                        bpf->len * sizeof(sf_single));
 628                 fmemcpy(&bpf->filter[bpf->len - 1], &sf_single,
 629                        sizeof(sf_single));
 630
 631                 fmemset(buff, 0, sizeof(buff));
 632         }
 633
 634         fclose(fp);
 635         if (bpf_validate(bpf) == 0)
 636                 panic("This is not a valid BPF program!\n");
 637 }