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bird/nest/a-path.c
Ondrej Zajicek (work) ec430a7fee Nest: Implement BGP path mask loop operator
Implement regex-like '+' operator in BGP path masks to match previous
path mask item multiple times. This is useful as ASNs may appear
multiple times in paths due to path prepending for traffic engineering
purposes.
2020-05-18 16:25:08 +02:00

906 lines
16 KiB
C

/*
* BIRD -- Path Operations
*
* (c) 2000 Martin Mares <mj@ucw.cz>
* (c) 2000 Pavel Machek <pavel@ucw.cz>
*
* Can be freely distributed and used under the terms of the GNU GPL.
*/
#include "nest/bird.h"
#include "nest/route.h"
#include "nest/attrs.h"
#include "lib/resource.h"
#include "lib/unaligned.h"
#include "lib/string.h"
#include "filter/data.h"
// static inline void put_as(byte *data, u32 as) { put_u32(data, as); }
// static inline u32 get_as(byte *data) { return get_u32(data); }
#define put_as put_u32
#define get_as get_u32
#define BS 4 /* Default block size of ASN (autonomous system number) */
#define BAD(DSC, VAL) ({ err_dsc = DSC; err_val = VAL; goto bad; })
int
as_path_valid(byte *data, uint len, int bs, int sets, int confed, char *err, uint elen)
{
byte *pos = data;
char *err_dsc = NULL;
uint err_val = 0;
while (len)
{
if (len < 2)
BAD("segment framing error", 0);
/* Process one AS path segment */
uint type = pos[0];
uint slen = 2 + bs * pos[1];
if (len < slen)
BAD("segment framing error", len);
switch (type)
{
case AS_PATH_SET:
if (!sets)
BAD("AS_SET segment", type);
break;
case AS_PATH_SEQUENCE:
break;
case AS_PATH_CONFED_SEQUENCE:
if (!confed)
BAD("AS_CONFED_SEQUENCE segment", type);
break;
case AS_PATH_CONFED_SET:
if (!sets || !confed)
BAD("AS_CONFED_SET segment", type);
break;
default:
BAD("unknown segment", type);
}
if (pos[1] == 0)
BAD("zero-length segment", type);
pos += slen;
len -= slen;
}
return 1;
bad:
if (err)
if (bsnprintf(err, elen, "%s (%u) at %d", err_dsc, err_val, (int) (pos - data)) < 0)
err[0] = 0;
return 0;
}
int
as_path_16to32(byte *dst, const byte *src, uint len)
{
byte *dst0 = dst;
const byte *end = src + len;
uint i, n;
while (src < end)
{
n = src[1];
*dst++ = *src++;
*dst++ = *src++;
for (i = 0; i < n; i++)
{
put_u32(dst, get_u16(src));
src += 2;
dst += 4;
}
}
return dst - dst0;
}
int
as_path_32to16(byte *dst, const byte *src, uint len)
{
byte *dst0 = dst;
const byte *end = src + len;
uint i, n;
while (src < end)
{
n = src[1];
*dst++ = *src++;
*dst++ = *src++;
for (i = 0; i < n; i++)
{
put_u16(dst, get_u32(src));
src += 4;
dst += 2;
}
}
return dst - dst0;
}
int
as_path_contains_as4(const struct adata *path)
{
const byte *pos = path->data;
const byte *end = pos + path->length;
uint i, n;
while (pos < end)
{
n = pos[1];
pos += 2;
for (i = 0; i < n; i++)
{
if (get_as(pos) > 0xFFFF)
return 1;
pos += BS;
}
}
return 0;
}
int
as_path_contains_confed(const struct adata *path)
{
const byte *pos = path->data;
const byte *end = pos + path->length;
while (pos < end)
{
uint type = pos[0];
uint slen = 2 + BS * pos[1];
if ((type == AS_PATH_CONFED_SEQUENCE) ||
(type == AS_PATH_CONFED_SET))
return 1;
pos += slen;
}
return 0;
}
struct adata *
as_path_strip_confed(struct linpool *pool, const struct adata *path)
{
struct adata *res = lp_alloc_adata(pool, path->length);
const byte *src = path->data;
const byte *end = src + path->length;
byte *dst = res->data;
while (src < end)
{
uint type = src[0];
uint slen = 2 + BS * src[1];
/* Copy regular segments */
if ((type == AS_PATH_SET) || (type == AS_PATH_SEQUENCE))
{
memcpy(dst, src, slen);
dst += slen;
}
src += slen;
}
/* Fix the result length */
res->length = dst - res->data;
return res;
}
struct adata *
as_path_prepend2(struct linpool *pool, const struct adata *op, int seq, u32 as)
{
struct adata *np;
const byte *pos = op->data;
uint len = op->length;
if (len && (pos[0] == seq) && (pos[1] < 255))
{
/* Starting with matching segment => just prepend the AS number */
np = lp_alloc_adata(pool, len + BS);
np->data[0] = seq;
np->data[1] = pos[1] + 1;
put_as(np->data + 2, as);
uint dlen = BS * pos[1];
memcpy(np->data + 2 + BS, pos + 2, dlen);
ADVANCE(pos, len, 2 + dlen);
}
else
{
/* Create a new path segment */
np = lp_alloc_adata(pool, len + 2 + BS);
np->data[0] = seq;
np->data[1] = 1;
put_as(np->data + 2, as);
}
if (len)
{
byte *dst = np->data + 2 + BS * np->data[1];
memcpy(dst, pos, len);
}
return np;
}
struct adata *
as_path_to_old(struct linpool *pool, const struct adata *path)
{
struct adata *res = lp_alloc_adata(pool, path->length);
byte *pos = res->data;
byte *end = pos + res->length;
uint i, n;
u32 as;
/* Copy the whole path */
memcpy(res->data, path->data, path->length);
/* Replace 32-bit AS numbers with AS_TRANS */
while (pos < end)
{
n = pos[1];
pos += 2;
for (i = 0; i < n; i++)
{
as = get_as(pos);
if (as > 0xFFFF)
put_as(pos, AS_TRANS);
pos += BS;
}
}
return res;
}
/*
* Cut the path to the length @num, measured to the usual path metric. Note that
* AS_CONFED_* segments have zero length and must be added if they are on edge.
*/
struct adata *
as_path_cut(struct linpool *pool, const struct adata *path, uint num)
{
const byte *pos = path->data;
const byte *end = pos + path->length;
while (pos < end)
{
uint t = pos[0];
uint l = pos[1];
uint n = 0;
switch (t)
{
case AS_PATH_SET: n = 1; break;
case AS_PATH_SEQUENCE: n = l; break;
case AS_PATH_CONFED_SEQUENCE: n = 0; break;
case AS_PATH_CONFED_SET: n = 0; break;
default: bug("as_path_cut: Invalid path segment");
}
/* Cannot add whole segment, so try partial one and finish */
if (num < n)
{
const byte *nend = pos;
if (num)
nend += 2 + BS * num;
struct adata *res = lp_alloc_adata(pool, path->length);
res->length = nend - (const byte *) path->data;
memcpy(res->data, path->data, res->length);
if (num)
{
byte *dpos = ((byte *) res->data) + (pos - (const byte *) path->data);
dpos[1] = num;
}
return res;
}
num -= n;
pos += 2 + BS * l;
}
struct adata *res = lp_alloc_adata(pool, path->length);
res->length = path->length;
memcpy(res->data, path->data, res->length);
return res;
}
/*
* Merge (concatenate) paths @p1 and @p2 and return the result.
* In contrast to other as_path_* functions, @p1 and @p2 may be reused.
*/
const struct adata *
as_path_merge(struct linpool *pool, const struct adata *p1, const struct adata *p2)
{
if (p1->length == 0)
return p2;
if (p2->length == 0)
return p1;
struct adata *res = lp_alloc_adata(pool, p1->length + p2->length);
memcpy(res->data, p1->data, p1->length);
memcpy(res->data + p1->length, p2->data, p2->length);
return res;
}
void
as_path_format(const struct adata *path, byte *bb, uint size)
{
buffer buf = { .start = bb, .pos = bb, .end = bb + size }, *b = &buf;
const byte *pos = path->data;
const byte *end = pos + path->length;
const char *ops, *cls;
b->pos[0] = 0;
while (pos < end)
{
uint type = pos[0];
uint len = pos[1];
pos += 2;
switch (type)
{
case AS_PATH_SET: ops = "{"; cls = "}"; break;
case AS_PATH_SEQUENCE: ops = NULL; cls = NULL; break;
case AS_PATH_CONFED_SEQUENCE: ops = "("; cls = ")"; break;
case AS_PATH_CONFED_SET: ops = "({"; cls = "})"; break;
default: bug("Invalid path segment");
}
if (ops)
buffer_puts(b, ops);
while (len--)
{
buffer_print(b, len ? "%u " : "%u", get_as(pos));
pos += BS;
}
if (cls)
buffer_puts(b, cls);
if (pos < end)
buffer_puts(b, " ");
}
/* Handle overflow */
if (b->pos == b->end)
strcpy(b->end - 12, "...");
}
int
as_path_getlen(const struct adata *path)
{
const byte *pos = path->data;
const byte *end = pos + path->length;
uint res = 0;
while (pos < end)
{
uint t = pos[0];
uint l = pos[1];
uint n = 0;
switch (t)
{
case AS_PATH_SET: n = 1; break;
case AS_PATH_SEQUENCE: n = l; break;
case AS_PATH_CONFED_SEQUENCE: n = 0; break;
case AS_PATH_CONFED_SET: n = 0; break;
default: bug("as_path_getlen: Invalid path segment");
}
res += n;
pos += 2 + BS * l;
}
return res;
}
int
as_path_get_last(const struct adata *path, u32 *orig_as)
{
const byte *pos = path->data;
const byte *end = pos + path->length;
int found = 0;
u32 val = 0;
while (pos < end)
{
uint type = pos[0];
uint len = pos[1];
pos += 2;
if (!len)
continue;
switch (type)
{
case AS_PATH_SET:
case AS_PATH_CONFED_SET:
found = 0;
break;
case AS_PATH_SEQUENCE:
case AS_PATH_CONFED_SEQUENCE:
val = get_as(pos + BS * (len - 1));
found = 1;
break;
default:
bug("Invalid path segment");
}
pos += BS * len;
}
if (found)
*orig_as = val;
return found;
}
u32
as_path_get_last_nonaggregated(const struct adata *path)
{
const byte *pos = path->data;
const byte *end = pos + path->length;
u32 val = 0;
while (pos < end)
{
uint type = pos[0];
uint len = pos[1];
pos += 2;
if (!len)
continue;
switch (type)
{
case AS_PATH_SET:
case AS_PATH_CONFED_SET:
return val;
case AS_PATH_SEQUENCE:
case AS_PATH_CONFED_SEQUENCE:
val = get_as(pos + BS * (len - 1));
break;
default:
bug("Invalid path segment");
}
pos += BS * len;
}
return val;
}
int
as_path_get_first(const struct adata *path, u32 *last_as)
{
const u8 *p = path->data;
if ((path->length == 0) || (p[0] != AS_PATH_SEQUENCE) || (p[1] == 0))
return 0;
*last_as = get_as(p+2);
return 1;
}
int
as_path_get_first_regular(const struct adata *path, u32 *last_as)
{
const byte *pos = path->data;
const byte *end = pos + path->length;
while (pos < end)
{
uint type = pos[0];
uint len = pos[1];
pos += 2;
switch (type)
{
case AS_PATH_SET:
return 0;
case AS_PATH_SEQUENCE:
if (len == 0)
return 0;
*last_as = get_as(pos);
return 1;
case AS_PATH_CONFED_SEQUENCE:
case AS_PATH_CONFED_SET:
break;
default:
bug("Invalid path segment");
}
pos += BS * len;
}
return 0;
}
int
as_path_contains(const struct adata *path, u32 as, int min)
{
const u8 *p = path->data;
const u8 *q = p+path->length;
int num = 0;
int i, n;
while (p<q)
{
n = p[1];
p += 2;
for(i=0; i<n; i++)
{
if (get_as(p) == as)
if (++num == min)
return 1;
p += BS;
}
}
return 0;
}
int
as_path_match_set(const struct adata *path, const struct f_tree *set)
{
const u8 *p = path->data;
const u8 *q = p+path->length;
int i, n;
while (p<q)
{
n = p[1];
p += 2;
for (i=0; i<n; i++)
{
struct f_val v = {T_INT, .val.i = get_as(p)};
if (find_tree(set, &v))
return 1;
p += BS;
}
}
return 0;
}
const struct adata *
as_path_filter(struct linpool *pool, const struct adata *path, const struct f_tree *set, u32 key, int pos)
{
if (!path)
return NULL;
int len = path->length;
const u8 *p = path->data;
const u8 *q = path->data + len;
u8 *d, *d2;
int i, bt, sn, dn;
u8 buf[len];
d = buf;
while (p<q)
{
/* Read block header (type and length) */
bt = p[0];
sn = p[1];
dn = 0;
p += 2;
d2 = d + 2;
for (i = 0; i < sn; i++)
{
u32 as = get_as(p);
int match;
if (set)
{
struct f_val v = {T_INT, .val.i = as};
match = !!find_tree(set, &v);
}
else
match = (as == key);
if (match == pos)
{
put_as(d2, as);
d2 += BS;
dn++;
}
p += BS;
}
if (dn > 0)
{
/* Nonempty block, set block header and advance */
d[0] = bt;
d[1] = dn;
d = d2;
}
}
uint nl = d - buf;
if (nl == path->length)
return path;
struct adata *res = lp_alloc(pool, sizeof(struct adata) + nl);
res->length = nl;
memcpy(res->data, buf, nl);
return res;
}
struct pm_pos
{
u8 set;
u8 mark;
union
{
const char *sp;
u32 asn;
} val;
};
static int
parse_path(const struct adata *path, struct pm_pos *pp)
{
const byte *pos = path->data;
const byte *end = pos + path->length;
struct pm_pos *op = pp;
uint i;
while (pos < end)
{
uint type = pos[0];
uint len = pos[1];
pos += 2;
switch (type)
{
case AS_PATH_SET:
case AS_PATH_CONFED_SET:
pp->set = 1;
pp->mark = 0;
pp->val.sp = pos - 1;
pp++;
pos += BS * len;
break;
case AS_PATH_SEQUENCE:
case AS_PATH_CONFED_SEQUENCE:
for (i = 0; i < len; i++)
{
pp->set = 0;
pp->mark = 0;
pp->val.asn = get_as(pos);
pp++;
pos += BS;
}
break;
default:
bug("Invalid path segment");
}
}
return pp - op;
}
static int
pm_match_val(const struct pm_pos *pos, u32 asn, u32 asn2)
{
u32 gas;
if (! pos->set)
return ((pos->val.asn >= asn) && (pos->val.asn <= asn2));
const u8 *p = pos->val.sp;
int len = *p++;
int i;
for (i = 0; i < len; i++)
{
gas = get_as(p + i * BS);
if ((gas >= asn) && (gas <= asn2))
return 1;
}
return 0;
}
static int
pm_match_set(const struct pm_pos *pos, const struct f_tree *set)
{
struct f_val asn = { .type = T_INT };
if (! pos->set)
{
asn.val.i = pos->val.asn;
return !!find_tree(set, &asn);
}
const u8 *p = pos->val.sp;
int len = *p++;
int i;
for (i = 0; i < len; i++)
{
asn.val.i = get_as(p + i * BS);
if (find_tree(set, &asn))
return 1;
}
return 0;
}
static inline int
pm_match(const struct pm_pos *pos, const struct f_path_mask_item *mask, u32 asn, u32 asn2)
{
return ((mask->kind == PM_QUESTION) ||
((mask->kind != PM_ASN_SET) ?
pm_match_val(pos, asn, asn2) :
pm_match_set(pos, mask->set)));
}
static void
pm_mark(struct pm_pos *pos, int *i, int plen, int *nl, int *nh)
{
int j = *i;
if (pos[j].set)
do { pos[j].mark = 1; j++; }
while ((j < plen) && pos[j].set);
else
j++;
pos[j].mark = 1;
/* Update low, high based on first and last marked pos */
int l = pos[*i].set ? *i : j;
*nl = (*nl < 0) ? l : MIN(*nl, l);
*nh = MAX(*nh, j);
*i = j;
}
/* AS path matching is nontrivial. Because AS path can
* contain sets, it is not a plain wildcard matching. A set
* in an AS path is interpreted as it might represent any
* sequence of AS numbers from that set (possibly with
* repetitions). So it is also a kind of a pattern,
* more complicated than a path mask.
*
* The algorithm for AS path matching is a variant
* of nondeterministic finite state machine, where
* positions in AS path are states, and items in
* path mask are input for that finite state machine.
* During execution of the algorithm we maintain a set
* of marked states - a state is marked if it can be
* reached by any walk through NFSM with regard to
* currently processed part of input. When we process
* next part of mask, we advance each marked state.
* We start with marked first position, when we
* run out of marked positions, we reject. When
* we process the whole mask, we accept if final position
* (auxiliary position after last real position in AS path)
* is marked.
*/
int
as_path_match(const struct adata *path, const struct f_path_mask *mask)
{
struct pm_pos pos[2048 + 1];
int plen = parse_path(path, pos);
int l, h, i, nh, nl, last, loop;
u32 val = 0;
u32 val2 = 0;
/* l and h are bound of interval of positions where
are marked states */
pos[plen].set = 0;
pos[plen].mark = 0;
l = h = loop = 0;
pos[0].mark = 1;
for (uint m=0; m < mask->len; m++)
{
/* We remove this mark to not step after pos[plen] */
pos[plen].mark = 0;
switch (mask->item[m].kind)
{
case PM_ASTERISK:
for (i = l; i <= plen; i++)
pos[i].mark = 1;
h = plen;
break;
case PM_LOOP:
loop = 1;
break;
case PM_ASN: /* Define single ASN as ASN..ASN - very narrow interval */
val2 = val = mask->item[m].asn;
goto step;
case PM_ASN_EXPR:
bug("Expressions should be evaluated on AS path mask construction.");
case PM_ASN_RANGE:
val = mask->item[m].from;
val2 = mask->item[m].to;
goto step;
case PM_QUESTION:
case PM_ASN_SET:
step:
nh = nl = -1;
last = plen;
for (i = h; i >= l; i--)
if (pos[i].mark)
{
pos[i].mark = 0;
int j = i;
match:
if (pm_match(pos + j, &mask->item[m], val, val2))
{
pm_mark(pos, &j, plen, &nl, &nh);
if (loop && (j < last))
goto match;
}
last = i;
}
if (nh < 0)
return 0;
h = nh;
l = nl;
loop = 0;
break;
}
}
return pos[plen].mark;
}