filter/filter.c

   1 /*
   2  *      Filters: utility functions
   3  *
   4  *      Copyright 1998 Pavel Machek <pavel@ucw.cz>
   5  *
   6  *      Can be freely distributed and used under the terms of the GNU GPL.
   7  *
   8  */
   9
  10 /**
  11  * DOC: Filters
  12  *
  13  * You can find sources of the filter language in |filter/|
  14  * directory. File |filter/config.Y| contains filter grammar and basically translates
  15  * the source from user into a tree of &f_inst structures. These trees are
  16  * later interpreted using code in |filter/filter.c|.
  17  *
  18  * A filter is represented by a tree of &f_inst structures, one structure per
  19  * "instruction". Each &f_inst contains @code, @aux value which is
  20  * usually the data type this instruction operates on and two generic
  21  * arguments (@a[0], @a[1]). Some instructions contain pointer(s) to other
  22  * instructions in their (@a[0], @a[1]) fields.
  23  *
  24  * Filters use a &f_val structure for their data. Each &f_val
  25  * contains type and value (types are constants prefixed with %T_). Few
  26  * of the types are special; %T_RETURN can be or-ed with a type to indicate
  27  * that return from a function or from the whole filter should be
  28  * forced. Important thing about &f_val's is that they may be copied
  29  * with a simple |=|. That's fine for all currently defined types: strings
  30  * are read-only (and therefore okay), paths are copied for each
  31  * operation (okay too).
  32  */
  33
  34 #undef LOCAL_DEBUG
  35
  36 #include "nest/bird.h"
  37 #include "lib/lists.h"
  38 #include "lib/resource.h"
  39 #include "lib/socket.h"
  40 #include "lib/string.h"
  41 #include "lib/unaligned.h"
  42 #include "lib/net.h"
  43 #include "lib/ip.h"
  44 #include "nest/route.h"
  45 #include "nest/protocol.h"
  46 #include "nest/iface.h"
  47 #include "nest/attrs.h"
  48 #include "conf/conf.h"
  49 #include "filter/filter.h"
  50 #include "filter/f-inst.h"
  51 #include "filter/data.h"
  52
  53
  54 /* Exception bits */
  55 enum f_exception {
  56   FE_RETURN = 0x1,
  57 };
  58
  59
  60 struct filter_stack {
  61   /* Value stack for execution */
  62 #define F_VAL_STACK_MAX 4096
  63   uint vcnt;                            /* Current value stack size; 0 for empty */
  64   uint ecnt;                            /* Current execute stack size; 0 for empty */
  65
  66   struct f_val vstk[F_VAL_STACK_MAX];   /* The stack itself */
  67
  68   /* Instruction stack for execution */
  69 #define F_EXEC_STACK_MAX 4096
  70   struct {
  71     const struct f_line *line;          /* The line that is being executed */
  72     uint pos;                           /* Instruction index in the line */
  73     uint ventry;                        /* Value stack depth on entry */
  74     uint vbase;                         /* Where to index variable positions from */
  75     enum f_exception emask;             /* Exception mask */
  76   } estk[F_EXEC_STACK_MAX];
  77 };
  78
  79 /* Internal filter state, to be allocated on stack when executing filters */
  80 struct filter_state {
  81   /* Stacks needed for execution */
  82   struct filter_stack *stack;
  83
  84   /* The route we are processing. This may be NULL to indicate no route available. */
  85   struct rte **rte;
  86
  87   /* The old rta to be freed after filters are done. */
  88   struct rta *old_rta;
  89
  90   /* Cached pointer to ea_list */
  91   struct ea_list **eattrs;
  92   struct linpool *pool;
  93   struct buffer buf;
  94   int flags;
  95 };
  96
  97 #if HAVE_THREAD_LOCAL
  98 _Thread_local static struct filter_state filter_state;
  99 _Thread_local static struct filter_stack filter_stack;
 100 #define FS_INIT(...)    filter_state = (struct filter_state) { .stack = &filter_stack, __VA_ARGS__ }
 101 #else
 102 #define FS_INIT(...)    struct filter_state filter_state = { .stack = alloca(sizeof(struct filter_stack)), __VA_ARGS__ };
 103 #endif
 104
 105 void (*bt_assert_hook)(int result, const struct f_line_item *assert);
 106
 107 static inline void f_cache_eattrs(struct filter_state *fs)
 108 {
 109   fs->eattrs = &((*fs->rte)->attrs->eattrs);
 110 }
 111
 112 static inline void f_rte_cow(struct filter_state *fs)
 113 {
 114   if (!((*fs->rte)->flags & REF_COW))
 115     return;
 116
 117   *fs->rte = rte_cow(*fs->rte);
 118 }
 119
 120 /*
 121  * rta_cow - prepare rta for modification by filter
 122  */
 123 static void
 124 f_rta_cow(struct filter_state *fs)
 125 {
 126   if (!rta_is_cached((*fs->rte)->attrs))
 127     return;
 128
 129   /* Prepare to modify rte */
 130   f_rte_cow(fs);
 131
 132   /* Store old rta to free it later, it stores reference from rte_cow() */
 133   fs->old_rta = (*fs->rte)->attrs;
 134
 135   /*
 136    * Get shallow copy of rta. Fields eattrs and nexthops of rta are shared
 137    * with fs->old_rta (they will be copied when the cached rta will be obtained
 138    * at the end of f_run()), also the lock of hostentry is inherited (we
 139    * suppose hostentry is not changed by filters).
 140    */
 141   (*fs->rte)->attrs = rta_do_cow((*fs->rte)->attrs, fs->pool);
 142
 143   /* Re-cache the ea_list */
 144   f_cache_eattrs(fs);
 145 }
 146
 147 static char *
 148 val_format_str(struct filter_state *fs, struct f_val *v) {
 149   buffer b;
 150   LOG_BUFFER_INIT(b);
 151   val_format(v, &b);
 152   return lp_strdup(fs->pool, b.start);
 153 }
 154
 155 static struct tbf rl_runtime_err = TBF_DEFAULT_LOG_LIMITS;
 156
 157 /**
 158  * interpret
 159  * @fs: filter state
 160  * @what: filter to interpret
 161  *
 162  * Interpret given tree of filter instructions. This is core function
 163  * of filter system and does all the hard work.
 164  *
 165  * Each instruction has 4 fields: code (which is instruction code),
 166  * aux (which is extension to instruction code, typically type),
 167  * arg1 and arg2 - arguments. Depending on instruction, arguments
 168  * are either integers, or pointers to instruction trees. Common
 169  * instructions like +, that have two expressions as arguments use
 170  * TWOARGS macro to get both of them evaluated.
 171  */
 172 static enum filter_return
 173 interpret(struct filter_state *fs, const struct f_line *line, struct f_val *val)
 174 {
 175   /* No arguments allowed */
 176   ASSERT(line->args == 0);
 177
 178   /* Initialize the filter stack */
 179   struct filter_stack *fstk = fs->stack;
 180
 181   fstk->vcnt = line->vars;
 182   memset(fstk->vstk, 0, sizeof(struct f_val) * line->vars);
 183
 184   /* The same as with the value stack. Not resetting the stack for performance reasons. */
 185   fstk->ecnt = 1;
 186   fstk->estk[0].line = line;
 187   fstk->estk[0].pos = 0;
 188
 189 #define curline fstk->estk[fstk->ecnt-1]
 190
 191 #if DEBUGGING
 192   debug("Interpreting line.");
 193   f_dump_line(line, 1);
 194 #endif
 195
 196   while (fstk->ecnt > 0) {
 197     while (curline.pos < curline.line->len) {
 198       const struct f_line_item *what = &(curline.line->items[curline.pos++]);
 199
 200       switch (what->fi_code) {
 201 #define res fstk->vstk[fstk->vcnt]
 202 #define v1 fstk->vstk[fstk->vcnt]
 203 #define v2 fstk->vstk[fstk->vcnt + 1]
 204 #define v3 fstk->vstk[fstk->vcnt + 2]
 205
 206 #define runtime(fmt, ...) do { \
 207   if (!(fs->flags & FF_SILENT)) \
 208     log_rl(&rl_runtime_err, L_ERR "filters, line %d: " fmt, what->lineno, ##__VA_ARGS__); \
 209   return F_ERROR; \
 210 } while(0)
 211
 212 #define ACCESS_RTE do { if (!fs->rte) runtime("No route to access"); } while (0)
 213 #define ACCESS_EATTRS do { if (!fs->eattrs) f_cache_eattrs(fs); } while (0)
 214
 215 #include "filter/inst-interpret.c"
 216 #undef res
 217 #undef v1
 218 #undef v2
 219 #undef v3
 220 #undef runtime
 221 #undef ACCESS_RTE
 222 #undef ACCESS_EATTRS
 223       }
 224     }
 225
 226     /* End of current line. Drop local variables before exiting. */
 227     fstk->vcnt -= curline.line->vars;
 228     fstk->vcnt -= curline.line->args;
 229     fstk->ecnt--;
 230   }
 231
 232   if (fstk->vcnt == 0) {
 233     if (val) {
 234       log_rl(&rl_runtime_err, L_ERR "filters: No value left on stack");
 235       return F_ERROR;
 236     }
 237     return F_NOP;
 238   }
 239
 240   if (val && (fstk->vcnt == 1)) {
 241     *val = fstk->vstk[0];
 242     return F_NOP;
 243   }
 244
 245   log_rl(&rl_runtime_err, L_ERR "Too many items left on stack: %u", fstk->vcnt);
 246   return F_ERROR;
 247 }
 248
 249
 250 /**
 251  * f_run - run a filter for a route
 252  * @filter: filter to run
 253  * @rte: route being filtered, may be modified
 254  * @tmp_pool: all filter allocations go from this pool
 255  * @flags: flags
 256  *
 257  * If filter needs to modify the route, there are several
 258  * posibilities. @rte might be read-only (with REF_COW flag), in that
 259  * case rw copy is obtained by rte_cow() and @rte is replaced. If
 260  * @rte is originally rw, it may be directly modified (and it is never
 261  * copied).
 262  *
 263  * The returned rte may reuse the (possibly cached, cloned) rta, or
 264  * (if rta was modified) contains a modified uncached rta, which
 265  * uses parts allocated from @tmp_pool and parts shared from original
 266  * rta. There is one exception - if @rte is rw but contains a cached
 267  * rta and that is modified, rta in returned rte is also cached.
 268  *
 269  * Ownership of cached rtas is consistent with rte, i.e.
 270  * if a new rte is returned, it has its own clone of cached rta
 271  * (and cached rta of read-only source rte is intact), if rte is
 272  * modified in place, old cached rta is possibly freed.
 273  */
 274 enum filter_return
 275 f_run(const struct filter *filter, struct rte **rte, struct linpool *tmp_pool, int flags)
 276 {
 277   if (filter == FILTER_ACCEPT)
 278     return F_ACCEPT;
 279
 280   if (filter == FILTER_REJECT)
 281     return F_REJECT;
 282
 283   int rte_cow = ((*rte)->flags & REF_COW);
 284   DBG( "Running filter `%s'...", filter->name );
 285
 286   /* Initialize the filter state */
 287   FS_INIT(
 288       .rte = rte,
 289       .pool = tmp_pool,
 290       .flags = flags,
 291       );
 292
 293   LOG_BUFFER_INIT(filter_state.buf);
 294
 295   /* Run the interpreter itself */
 296   enum filter_return fret = interpret(&filter_state, filter->root, NULL);
 297
 298   if (filter_state.old_rta) {
 299     /*
 300      * Cached rta was modified and filter_state->rte contains now an uncached one,
 301      * sharing some part with the cached one. The cached rta should
 302      * be freed (if rte was originally COW, filter_state->old_rta is a clone
 303      * obtained during rte_cow()).
 304      *
 305      * This also implements the exception mentioned in f_run()
 306      * description. The reason for this is that rta reuses parts of
 307      * filter_state->old_rta, and these may be freed during rta_free(filter_state->old_rta).
 308      * This is not the problem if rte was COW, because original rte
 309      * also holds the same rta.
 310      */
 311     if (!rte_cow) {
 312       /* Cache the new attrs */
 313       (*filter_state.rte)->attrs = rta_lookup((*filter_state.rte)->attrs);
 314
 315       /* Drop cached ea_list pointer */
 316       filter_state.eattrs = NULL;
 317     }
 318
 319     /* Uncache the old attrs and drop the pointer as it is invalid now. */
 320     rta_free(filter_state.old_rta);
 321     filter_state.old_rta = NULL;
 322   }
 323
 324   /* Process the filter output, log it and return */
 325   if (fret < F_ACCEPT) {
 326     if (!(filter_state.flags & FF_SILENT))
 327       log_rl(&rl_runtime_err, L_ERR "Filter %s did not return accept nor reject. Make up your mind", filter_name(filter));
 328     return F_ERROR;
 329   }
 330   DBG( "done (%u)\n", res.val.i );
 331   return fret;
 332 }
 333
 334 /**
 335  * f_eval_rte – run a filter line for an uncached route
 336  * @expr: filter line to run
 337  * @rte: route being filtered, may be modified
 338  * @tmp_pool: all filter allocations go from this pool
 339  *
 340  * This specific filter entry point runs the given filter line
 341  * (which must not have any arguments) on the given route.
 342  *
 343  * The route MUST NOT have REF_COW set and its attributes MUST NOT
 344  * be cached by rta_lookup().
 345  */
 346
 347 enum filter_return
 348 f_eval_rte(const struct f_line *expr, struct rte **rte, struct linpool *tmp_pool)
 349 {
 350   FS_INIT(
 351       .rte = rte,
 352       .pool = tmp_pool,
 353       );
 354
 355   LOG_BUFFER_INIT(filter_state.buf);
 356
 357   ASSERT(!((*rte)->flags & REF_COW));
 358   ASSERT(!rta_is_cached((*rte)->attrs));
 359
 360   return interpret(&filter_state, expr, NULL);
 361 }
 362
 363 /*
 364  * f_eval – get a value of a term
 365  * @expr: filter line containing the term
 366  * @tmp_pool: long data may get allocated from this pool
 367  * @pres: here the output will be stored
 368  */
 369 enum filter_return
 370 f_eval(const struct f_line *expr, struct linpool *tmp_pool, struct f_val *pres)
 371 {
 372   FS_INIT(
 373       .pool = tmp_pool,
 374       );
 375
 376   LOG_BUFFER_INIT(filter_state.buf);
 377
 378   enum filter_return fret = interpret(&filter_state, expr, pres);
 379   return fret;
 380 }
 381
 382 /*
 383  * f_eval_int – get an integer value of a term
 384  * Called internally from the config parser, uses its internal memory pool
 385  * for allocations. Do not call in other cases.
 386  */
 387 uint
 388 f_eval_int(const struct f_line *expr)
 389 {
 390   /* Called independently in parse-time to eval expressions */
 391   FS_INIT(
 392       .pool = cfg_mem,
 393       );
 394
 395   struct f_val val;
 396
 397   LOG_BUFFER_INIT(filter_state.buf);
 398
 399   if (interpret(&filter_state, expr, &val) > F_RETURN)
 400     cf_error("Runtime error while evaluating expression");
 401
 402   if (val.type != T_INT)
 403     cf_error("Integer expression expected");
 404
 405   return val.val.i;
 406 }
 407
 408 /*
 409  * f_eval_buf – get a value of a term and print it to the supplied buffer
 410  */
 411 enum filter_return
 412 f_eval_buf(const struct f_line *expr, struct linpool *tmp_pool, buffer *buf)
 413 {
 414   struct f_val val;
 415   enum filter_return fret = f_eval(expr, tmp_pool, &val);
 416   if (fret > F_RETURN)
 417     val_format(&val, buf);
 418   return fret;
 419 }
 420
 421 /**
 422  * filter_same - compare two filters
 423  * @new: first filter to be compared
 424  * @old: second filter to be compared
 425  *
 426  * Returns 1 in case filters are same, otherwise 0. If there are
 427  * underlying bugs, it will rather say 0 on same filters than say
 428  * 1 on different.
 429  */
 430 int
 431 filter_same(const struct filter *new, const struct filter *old)
 432 {
 433   if (old == new)       /* Handle FILTER_ACCEPT and FILTER_REJECT */
 434     return 1;
 435   if (old == FILTER_ACCEPT || old == FILTER_REJECT ||
 436       new == FILTER_ACCEPT || new == FILTER_REJECT)
 437     return 0;
 438
 439   if ((!old->sym) && (!new->sym))
 440     return f_same(new->root, old->root);
 441
 442   if ((!old->sym) || (!new->sym))
 443     return 0;
 444
 445   if (strcmp(old->sym->name, new->sym->name))
 446     return 0;
 447
 448   return new->sym->flags & SYM_FLAG_SAME;
 449 }
 450
 451 /**
 452  * filter_commit - do filter comparisons on all the named functions and filters
 453  */
 454 void
 455 filter_commit(const struct config *new, const struct config *old)
 456 {
 457   if (!old)
 458     return;
 459
 460   struct symbol *sym, *osym;
 461   WALK_LIST(sym, new->symbols)
 462     switch (sym->class) {
 463       case SYM_FUNCTION:
 464         if ((osym = cf_find_symbol(old, sym->name)) &&
 465             (osym->class == SYM_FUNCTION) &&
 466             f_same(sym->function, osym->function))
 467           sym->flags |= SYM_FLAG_SAME;
 468         else
 469           sym->flags &= ~SYM_FLAG_SAME;
 470         break;
 471
 472       case SYM_FILTER:
 473         if ((osym = cf_find_symbol(old, sym->name)) &&
 474             (osym->class == SYM_FILTER) &&
 475             f_same(sym->filter->root, osym->filter->root))
 476           sym->flags |= SYM_FLAG_SAME;
 477         else
 478           sym->flags &= ~SYM_FLAG_SAME;
 479         break;
 480     }
 481 }