bird/filter/filter.c
Maria Matejka d1039926f5 Filter: Interpreter merged into the common m4 generator.
The config-time partial evaluation of constant expressions in filters is nearby.
2019-02-20 22:30:55 +01:00

382 lines
10 KiB
C

/*
* Filters: utility functions
*
* Copyright 1998 Pavel Machek <pavel@ucw.cz>
*
* Can be freely distributed and used under the terms of the GNU GPL.
*
*/
/**
* DOC: Filters
*
* You can find sources of the filter language in |filter/|
* directory. File |filter/config.Y| contains filter grammar and basically translates
* the source from user into a tree of &f_inst structures. These trees are
* later interpreted using code in |filter/filter.c|.
*
* A filter is represented by a tree of &f_inst structures, one structure per
* "instruction". Each &f_inst contains @code, @aux value which is
* usually the data type this instruction operates on and two generic
* arguments (@a[0], @a[1]). Some instructions contain pointer(s) to other
* instructions in their (@a[0], @a[1]) fields.
*
* Filters use a &f_val structure for their data. Each &f_val
* contains type and value (types are constants prefixed with %T_). Few
* of the types are special; %T_RETURN can be or-ed with a type to indicate
* that return from a function or from the whole filter should be
* forced. Important thing about &f_val's is that they may be copied
* with a simple |=|. That's fine for all currently defined types: strings
* are read-only (and therefore okay), paths are copied for each
* operation (okay too).
*/
#undef LOCAL_DEBUG
#include "nest/bird.h"
#include "lib/lists.h"
#include "lib/resource.h"
#include "lib/socket.h"
#include "lib/string.h"
#include "lib/unaligned.h"
#include "lib/net.h"
#include "lib/ip.h"
#include "nest/route.h"
#include "nest/protocol.h"
#include "nest/iface.h"
#include "nest/attrs.h"
#include "conf/conf.h"
#include "filter/filter.h"
#include "filter/f-inst.h"
#include "filter/data.h"
/* Internal filter state, to be allocated on stack when executing filters */
struct filter_state {
struct rte **rte;
struct rta *old_rta;
struct ea_list **eattrs;
struct linpool *pool;
struct buffer buf;
int flags;
};
void (*bt_assert_hook)(int result, const struct f_line_item *assert);
static inline void f_cache_eattrs(struct filter_state *fs)
{
fs->eattrs = &((*fs->rte)->attrs->eattrs);
}
static inline void f_rte_cow(struct filter_state *fs)
{
if (!((*fs->rte)->flags & REF_COW))
return;
*fs->rte = rte_cow(*fs->rte);
}
/*
* rta_cow - prepare rta for modification by filter
*/
static void
f_rta_cow(struct filter_state *fs)
{
if (!rta_is_cached((*fs->rte)->attrs))
return;
/* Prepare to modify rte */
f_rte_cow(fs);
/* Store old rta to free it later, it stores reference from rte_cow() */
fs->old_rta = (*fs->rte)->attrs;
/*
* Get shallow copy of rta. Fields eattrs and nexthops of rta are shared
* with fs->old_rta (they will be copied when the cached rta will be obtained
* at the end of f_run()), also the lock of hostentry is inherited (we
* suppose hostentry is not changed by filters).
*/
(*fs->rte)->attrs = rta_do_cow((*fs->rte)->attrs, fs->pool);
/* Re-cache the ea_list */
f_cache_eattrs(fs);
}
static char *
val_format_str(struct filter_state *fs, struct f_val *v) {
buffer b;
LOG_BUFFER_INIT(b);
val_format(v, &b);
return lp_strdup(fs->pool, b.start);
}
static struct tbf rl_runtime_err = TBF_DEFAULT_LOG_LIMITS;
/**
* interpret
* @fs: filter state
* @what: filter to interpret
*
* Interpret given tree of filter instructions. This is core function
* of filter system and does all the hard work.
*
* Each instruction has 4 fields: code (which is instruction code),
* aux (which is extension to instruction code, typically type),
* arg1 and arg2 - arguments. Depending on instruction, arguments
* are either integers, or pointers to instruction trees. Common
* instructions like +, that have two expressions as arguments use
* TWOARGS macro to get both of them evaluated.
*/
static enum filter_return
interpret(struct filter_state *fs, const struct f_line *line, struct f_val *val)
{
#define F_VAL_STACK_MAX 4096
/* Value stack for execution */
struct f_val_stack {
uint cnt; /* Current stack size; 0 for empty */
struct f_val val[F_VAL_STACK_MAX]; /* The stack itself */
} vstk;
/* The stack itself is intentionally kept as-is for performance reasons.
* Do NOT rewrite this to initialization by struct literal. It's slow.
*/
vstk.cnt = 0;
#define F_EXEC_STACK_MAX 4096
/* Exception bits */
enum f_exception {
FE_RETURN = 0x1,
};
/* Instruction stack for execution */
struct f_exec_stack {
struct {
const struct f_line *line; /* The line that is being executed */
uint pos; /* Instruction index in the line */
uint ventry; /* Value stack depth on entry */
enum f_exception emask; /* Exception mask */
} item[F_EXEC_STACK_MAX];
uint cnt; /* Current stack size; 0 for empty */
} estk;
/* The same as with the value stack. Not resetting the stack for performance reasons. */
estk.cnt = 1;
estk.item[0].line = line;
estk.item[0].pos = 0;
#define curline estk.item[estk.cnt-1]
#if DEBUGGING
debug("Interpreting line.");
f_dump_line(line, 1);
#endif
while (estk.cnt > 0) {
while (curline.pos < curline.line->len) {
const struct f_line_item *what = &(curline.line->items[curline.pos++]);
switch (what->fi_code) {
#define res vstk.val[vstk.cnt]
#define v1 vstk.val[vstk.cnt]
#define v2 vstk.val[vstk.cnt + 1]
#define v3 vstk.val[vstk.cnt + 2]
#define runtime(fmt, ...) do { \
if (!(fs->flags & FF_SILENT)) \
log_rl(&rl_runtime_err, L_ERR "filters, line %d: " fmt, what->lineno, ##__VA_ARGS__); \
return F_ERROR; \
} while(0)
#define ACCESS_RTE do { if (!fs->rte) runtime("No route to access"); } while (0)
#define ACCESS_EATTRS do { if (!fs->eattrs) f_cache_eattrs(fs); } while (0)
#include "filter/inst-interpret.c"
#undef res
#undef v1
#undef v2
#undef v3
#undef runtime
#undef ACCESS_RTE
#undef ACCESS_EATTRS
}
}
estk.cnt--;
}
switch (vstk.cnt) {
case 0:
if (val) {
log_rl(&rl_runtime_err, L_ERR "filters: No value left on stack");
return F_ERROR;
}
return F_NOP;
case 1:
if (val) {
*val = vstk.val[0];
return F_NOP;
}
/* fallthrough */
default:
log_rl(&rl_runtime_err, L_ERR "Too many items left on stack: %u", vstk.cnt);
return F_ERROR;
}
}
/**
* f_run - run a filter for a route
* @filter: filter to run
* @rte: route being filtered, may be modified
* @tmp_pool: all filter allocations go from this pool
* @flags: flags
*
* If filter needs to modify the route, there are several
* posibilities. @rte might be read-only (with REF_COW flag), in that
* case rw copy is obtained by rte_cow() and @rte is replaced. If
* @rte is originally rw, it may be directly modified (and it is never
* copied).
*
* The returned rte may reuse the (possibly cached, cloned) rta, or
* (if rta was modificied) contains a modified uncached rta, which
* uses parts allocated from @tmp_pool and parts shared from original
* rta. There is one exception - if @rte is rw but contains a cached
* rta and that is modified, rta in returned rte is also cached.
*
* Ownership of cached rtas is consistent with rte, i.e.
* if a new rte is returned, it has its own clone of cached rta
* (and cached rta of read-only source rte is intact), if rte is
* modified in place, old cached rta is possibly freed.
*/
enum filter_return
f_run(const struct filter *filter, struct rte **rte, struct linpool *tmp_pool, int flags)
{
if (filter == FILTER_ACCEPT)
return F_ACCEPT;
if (filter == FILTER_REJECT)
return F_REJECT;
int rte_cow = ((*rte)->flags & REF_COW);
DBG( "Running filter `%s'...", filter->name );
struct filter_state fs = {
.rte = rte,
.pool = tmp_pool,
.flags = flags,
};
LOG_BUFFER_INIT(fs.buf);
enum filter_return fret = interpret(&fs, filter->root, NULL);
if (fs.old_rta) {
/*
* Cached rta was modified and fs->rte contains now an uncached one,
* sharing some part with the cached one. The cached rta should
* be freed (if rte was originally COW, fs->old_rta is a clone
* obtained during rte_cow()).
*
* This also implements the exception mentioned in f_run()
* description. The reason for this is that rta reuses parts of
* fs->old_rta, and these may be freed during rta_free(fs->old_rta).
* This is not the problem if rte was COW, because original rte
* also holds the same rta.
*/
if (!rte_cow)
(*fs.rte)->attrs = rta_lookup((*fs.rte)->attrs);
rta_free(fs.old_rta);
}
if (fret < F_ACCEPT) {
if (!(fs.flags & FF_SILENT))
log_rl(&rl_runtime_err, L_ERR "Filter %s did not return accept nor reject. Make up your mind", filter->name);
return F_ERROR;
}
DBG( "done (%u)\n", res.val.i );
return fret;
}
/* TODO: perhaps we could integrate f_eval(), f_eval_rte() and f_run() */
enum filter_return
f_eval_rte(const struct f_line *expr, struct rte **rte, struct linpool *tmp_pool)
{
struct filter_state fs = {
.rte = rte,
.pool = tmp_pool,
};
LOG_BUFFER_INIT(fs.buf);
/* Note that in this function we assume that rte->attrs is private / uncached */
return interpret(&fs, expr, NULL);
}
enum filter_return
f_eval(const struct f_line *expr, struct linpool *tmp_pool, struct f_val *pres)
{
struct filter_state fs = {
.pool = tmp_pool,
};
LOG_BUFFER_INIT(fs.buf);
enum filter_return fret = interpret(&fs, expr, pres);
return fret;
}
uint
f_eval_int(const struct f_line *expr)
{
/* Called independently in parse-time to eval expressions */
struct filter_state fs = {
.pool = cfg_mem,
};
struct f_val val;
LOG_BUFFER_INIT(fs.buf);
if (interpret(&fs, expr, &val) > F_RETURN)
cf_error("Runtime error while evaluating expression");
if (val.type != T_INT)
cf_error("Integer expression expected");
return val.val.i;
}
enum filter_return
f_eval_buf(const struct f_line *expr, struct linpool *tmp_pool, buffer *buf)
{
struct f_val val;
enum filter_return fret = f_eval(expr, tmp_pool, &val);
if (fret > F_RETURN)
val_format(&val, buf);
return fret;
}
/**
* filter_same - compare two filters
* @new: first filter to be compared
* @old: second filter to be compared
*
* Returns 1 in case filters are same, otherwise 0. If there are
* underlying bugs, it will rather say 0 on same filters than say
* 1 on different.
*/
int
filter_same(const struct filter *new, const struct filter *old)
{
if (old == new) /* Handle FILTER_ACCEPT and FILTER_REJECT */
return 1;
if (old == FILTER_ACCEPT || old == FILTER_REJECT ||
new == FILTER_ACCEPT || new == FILTER_REJECT)
return 0;
return f_same(new->root, old->root);
}