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bird/nest/a-path.c
Ondrej Zajicek 949bd34e81 Fixes bug related to AS2->AS4 conversion.
2009-08-25 19:01:37 +02:00

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/*
* 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"
/* Global AS4 support, shared by all BGP instances.
* This specifies whether BA_AS_PATH attributes contain 2 or 4 B per ASN
*/
int bgp_as4_support = 1;
static void
put_as(byte *data, u32 as)
{
if (bgp_as4_support)
put_u32(data, as);
else if (as <= 0xFFFF)
put_u16(data, as);
else
bug("put_as: Try to put 32bit AS to 16bit AS Path");
}
static inline u32
get_as(byte *data)
{
return bgp_as4_support ? get_u32(data) : get_u16(data);
}
struct adata *
as_path_prepend(struct linpool *pool, struct adata *olda, u32 as)
{
int bs = bgp_as4_support ? 4 : 2;
struct adata *newa;
if (olda->length && olda->data[0] == AS_PATH_SEQUENCE && olda->data[1] < 255)
/* Starting with sequence => just prepend the AS number */
{
int nl = olda->length + bs;
newa = lp_alloc(pool, sizeof(struct adata) + nl);
newa->length = nl;
newa->data[0] = AS_PATH_SEQUENCE;
newa->data[1] = olda->data[1] + 1;
memcpy(newa->data + bs + 2, olda->data + 2, olda->length - 2);
}
else /* Create new path segment */
{
int nl = olda->length + bs + 2;
newa = lp_alloc(pool, sizeof(struct adata) + nl);
newa->length = nl;
newa->data[0] = AS_PATH_SEQUENCE;
newa->data[1] = 1;
memcpy(newa->data + bs + 2, olda->data, olda->length);
}
put_as(newa->data + 2, as);
return newa;
}
int
as_path_convert_to_old(struct adata *path, byte *dst, int *new_used)
{
byte *src = path->data;
byte *src_end = src + path->length;
byte *dst_start = dst;
u32 as;
int i, n;
*new_used = 0;
while (src < src_end)
{
n = src[1];
*dst++ = *src++;
*dst++ = *src++;
for(i=0; i<n; i++)
{
as = get_u32(src);
if (as > 0xFFFF)
{
as = AS_TRANS;
*new_used = 1;
}
put_u16(dst, as);
src += 4;
dst += 2;
}
}
return dst - dst_start;
}
int
as_path_convert_to_new(struct adata *path, byte *dst, int req_as)
{
byte *src = path->data;
byte *src_end = src + path->length;
byte *dst_start = dst;
u32 as;
int i, t, n;
while ((src < src_end) && (req_as > 0))
{
t = *src++;
n = *src++;
if (t == AS_PATH_SEQUENCE)
{
if (n > req_as)
n = req_as;
req_as -= n;
}
else // t == AS_PATH_SET
req_as--;
*dst++ = t;
*dst++ = n;
for(i=0; i<n; i++)
{
as = get_u16(src);
put_u32(dst, as);
src += 2;
dst += 4;
}
}
return dst - dst_start;
}
void
as_path_format(struct adata *path, byte *buf, unsigned int size)
{
int bs = bgp_as4_support ? 4 : 2;
byte *p = path->data;
byte *e = p + path->length;
byte *end = buf + size - 16;
int sp = 1;
int l, isset;
while (p < e)
{
if (buf > end)
{
strcpy(buf, " ...");
return;
}
isset = (*p++ == AS_PATH_SET);
l = *p++;
if (isset)
{
if (!sp)
*buf++ = ' ';
*buf++ = '{';
sp = 0;
}
while (l-- && buf <= end)
{
if (!sp)
*buf++ = ' ';
buf += bsprintf(buf, "%u", get_as(p));
p += bs;
sp = 0;
}
if (isset)
{
*buf++ = ' ';
*buf++ = '}';
sp = 0;
}
}
*buf = 0;
}
int
as_path_getlen(struct adata *path)
{
int bs = bgp_as4_support ? 4 : 2;
return as_path_getlen_int(path, bs);
}
int
as_path_getlen_int(struct adata *path, int bs)
{
int res = 0;
u8 *p = path->data;
u8 *q = p+path->length;
int len;
while (p<q)
{
switch (*p++)
{
case AS_PATH_SET: len = *p++; res++; p += bs * len; break;
case AS_PATH_SEQUENCE: len = *p++; res += len; p += bs * len; break;
default: bug("as_path_getlen: Invalid path segment");
}
}
return res;
}
int
as_path_get_first(struct adata *path, u32 *orig_as)
{
int bs = bgp_as4_support ? 4 : 2;
int found = 0;
u32 res = 0;
u8 *p = path->data;
u8 *q = p+path->length;
int len;
while (p<q)
{
switch (*p++)
{
case AS_PATH_SET:
if (len = *p++)
{
found = 1;
res = get_as(p);
p += bs * len;
}
break;
case AS_PATH_SEQUENCE:
if (len = *p++)
{
found = 1;
res = get_as(p + bs * (len - 1));
p += bs * len;
}
break;
default: bug("as_path_get_first: Invalid path segment");
}
}
*orig_as = res;
return found;
}
int
as_path_get_last(struct adata *path, u32 *last_as)
{
u8 *p = path->data;
if ((path->length == 0) || (p[0] != AS_PATH_SEQUENCE) || (p[1] == 0))
return 0;
else
{
*last_as = get_as(p+2);
return 1;
}
}
int
as_path_is_member(struct adata *path, u32 as)
{
int bs = bgp_as4_support ? 4 : 2;
u8 *p = path->data;
u8 *q = p+path->length;
int i, n;
while (p<q)
{
n = p[1];
p += 2;
for(i=0; i<n; i++)
{
if (get_as(p) == as)
return 1;
p += bs;
}
}
return 0;
}
struct pm_pos
{
u8 set;
u8 mark;
union
{
char *sp;
u32 asn;
} val;
};
static int
parse_path(struct adata *path, struct pm_pos *pos)
{
int bs = bgp_as4_support ? 4 : 2;
u8 *p = path->data;
u8 *q = p + path->length;
struct pm_pos *opos = pos;
int i, j, len;
while (p < q)
switch (*p++)
{
case AS_PATH_SET:
pos->set = 1;
pos->mark = 0;
pos->val.sp = p;
len = *p;
p += 1 + bs * len;
pos++;
break;
case AS_PATH_SEQUENCE:
len = *p++;
for (i = 0; i < len; i++)
{
pos->set = 0;
pos->mark = 0;
pos->val.asn = get_as(p);
p += bs;
pos++;
}
break;
default:
bug("as_path_match: Invalid path component");
}
return pos - opos;
}
static int
pm_match(struct pm_pos *pos, u32 asn)
{
if (! pos->set)
return pos->val.asn == asn;
int bs = bgp_as4_support ? 4 : 2;
u8 *p = pos->val.sp;
int len = *p++;
int i;
for (i = 0; i < len; i++)
if (get_as(p + i * bs) == asn)
return 1;
return 0;
}
static void
pm_mark(struct pm_pos *pos, int i, int plen, int *nl, int *nh)
{
int j;
if (pos[i].set)
pos[i].mark = 1;
for (j = i + 1; (j < plen) && pos[j].set && (! pos[j].mark); j++)
pos[j].mark = 1;
pos[j].mark = 1;
/* We are going downwards, therefore every mark is
new low and just the first mark is new high */
*nl = i + (pos[i].set ? 0 : 1);
if (*nh < 0)
*nh = 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 iff final position
* (auxiliary position after last real position in AS path)
* is marked.
*/
int
as_path_match(struct adata *path, struct f_path_mask *mask)
{
struct pm_pos pos[2048 + 1];
int plen = parse_path(path, pos);
int l, h, i, nh, nl;
u32 val;
/* l and h are bound of interval of positions where
are marked states */
pos[plen].set = 0;
pos[plen].mark = 0;
l = h = 0;
pos[0].mark = 1;
while (mask)
{
/* We remove this mark to not step after pos[plen] */
pos[plen].mark = 0;
switch (mask->kind)
{
case PM_ASTERISK:
for (i = l; i <= plen; i++)
pos[i].mark = 1;
h = plen;
break;
case PM_ASN:
val = mask->val;
goto step;
case PM_ASN_EXPR:
val = f_eval_asn((struct f_inst *) mask->val);
goto step;
case PM_QUESTION:
step:
nh = -1;
for (i = h; i >= l; i--)
if (pos[i].mark)
{
pos[i].mark = 0;
if ((mask->kind == PM_QUESTION) || pm_match(pos + i, val))
pm_mark(pos, i, plen, &nl, &nh);
}
if (nh < 0)
return 0;
h = nh;
l = nl;
break;
}
mask = mask->next;
}
return pos[plen].mark;
}
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