Claudio Jeker([email protected]) on 2018.08.09 21:59:16 +0200:
> On Thu, Aug 09, 2018 at 03:10:11PM +0200, Claudio Jeker wrote:
> > Per rfc6472 AS_SET should no longer be used but some AS still do.
> > Until now source-as would take the rightmost AS number of an AS_PATH no
> > matter if it was an AS_SEQUENCE or an AS_SET. Thit is not correct. Also
> > because AS_SET are used in aggregation source-as should match against the
> > aggregator AS (which it the rightmost as of the previous AS_PATH segment).
> > At the same time move the peer-as check out of the loop, there is no
> > reason to have that inside the for loop.
> >
> > This diff implements this and also makes aspath_extract() and the lenght
> > checks a bit more paranoid.
>
> OK, updated diff here that adds three things.
> a) it passes the filter_as struct to as_compare
> b) it ensures that if for whatever crazy reason AS 0 is passed to the
> filter it will not match (no matter what). This is more paranoia.
> I decided to do that since util.c is shared between bgpd and bgpctl
> and so the easy way of calling fatalx() is not an option here.
> c) fix the souce-as 42 >< 4242 case. Currently the >< operator is not
> correctly implemented it is more a <> as in inside but excluding the
> edges. I think 42 >< 4242 should match for AS 1 - 41 and 4243 and
> higher.
>
> Is this still OK?
hm. yes. ok.
although this will cause bizarre effects:
deny from any AS 0
wont match even for as == 0.
i have to admit that we check for AS 0 in the path somewhere else.
still...
> --
> :wq Claudio
>
>
> Index: bgpd.h
> ===================================================================
> RCS file: /cvs/src/usr.sbin/bgpd/bgpd.h,v
> retrieving revision 1.329
> diff -u -p -r1.329 bgpd.h
> --- bgpd.h 8 Aug 2018 14:29:05 -0000 1.329
> +++ bgpd.h 9 Aug 2018 19:43:39 -0000
> @@ -1156,8 +1156,6 @@ int aspath_snprint(char *, size_t, voi
> int aspath_asprint(char **, void *, u_int16_t);
> size_t aspath_strlen(void *, u_int16_t);
> int aspath_match(void *, u_int16_t, struct filter_as *, u_int32_t);
> -int as_compare(u_int8_t, u_int32_t, u_int32_t, u_int32_t,
> - u_int32_t);
> u_int32_t aspath_extract(const void *, int);
> int aspath_verify(void *, u_int16_t, int);
> #define AS_ERR_LEN -1
> Index: util.c
> ===================================================================
> RCS file: /cvs/src/usr.sbin/bgpd/util.c,v
> retrieving revision 1.28
> diff -u -p -r1.28 util.c
> --- util.c 22 Jul 2018 16:52:27 -0000 1.28
> +++ util.c 9 Aug 2018 19:38:34 -0000
> @@ -312,6 +312,22 @@ aspath_strlen(void *data, u_int16_t len)
> return (total_size);
> }
>
> +static int
> +as_compare(struct filter_as *f, u_int32_t as, u_int32_t match)
> +{
> + if (as == 0) /* AS 0 is invalid and therefor never matches */
> + return (0);
> + if ((f->op == OP_NONE || f->op == OP_EQ) && as == match)
> + return (1);
> + else if (f->op == OP_NE && as != match)
> + return (1);
> + else if (f->op == OP_RANGE && as >= f->as_min && as <= f->as_max)
> + return (1);
> + else if (f->op == OP_XRANGE && (as < f->as_min || as > f->as_max))
> + return (1);
> + return (0);
> +}
> +
> /* we need to be able to search more than one as */
> int
> aspath_match(void *data, u_int16_t len, struct filter_as *f, u_int32_t match)
> @@ -320,7 +336,7 @@ aspath_match(void *data, u_int16_t len,
> int final;
> u_int16_t seg_size;
> u_int8_t i, seg_len;
> - u_int32_t as;
> + u_int32_t as = 0, preas;
>
> if (f->type == AS_EMPTY) {
> if (len == 0)
> @@ -330,27 +346,35 @@ aspath_match(void *data, u_int16_t len,
> }
>
> seg = data;
> - for (; len > 0; len -= seg_size, seg += seg_size) {
> +
> + /* just check the first (leftmost) AS */
> + if (f->type == AS_PEER && len >= 6) {
> + as = aspath_extract(seg, 0);
> + if (as_compare(f, as, match))
> + return (1);
> + else
> + return (0);
> + }
> +
> + for (; len >= 6; len -= seg_size, seg += seg_size) {
> seg_len = seg[1];
> seg_size = 2 + sizeof(u_int32_t) * seg_len;
>
> final = (len == seg_size);
>
> - /* just check the first (leftmost) AS */
> - if (f->type == AS_PEER) {
> - as = aspath_extract(seg, 0);
> - if (as_compare(f->op, as, match, f->as_min, f->as_max))
> - return (1);
> - else
> - return (0);
> - }
> /* just check the final (rightmost) AS */
> if (f->type == AS_SOURCE) {
> + /* extract the rightmost AS and keep the one before */
> + preas = as;
> + as = aspath_extract(seg, seg_len - 1);
> /* not yet in the final segment */
> if (!final)
> continue;
> - as = aspath_extract(seg, seg_len - 1);
> - if (as_compare(f->op, as, match, f->as_min, f->as_max))
> + if (seg[0] == AS_SET)
> + /* use aggregator AS per rfc6472 */
> + if (preas)
> + as = preas;
> + if (as_compare(f, as, match))
> return (1);
> else
> return (0);
> @@ -364,32 +388,17 @@ aspath_match(void *data, u_int16_t len,
> if (final && i == seg_len - 1 && f->type == AS_TRANSIT)
> return (0);
> as = aspath_extract(seg, i);
> - if (as_compare(f->op, as, match, f->as_min, f->as_max))
> + if (as_compare(f, as, match))
> return (1);
> }
> }
> return (0);
> }
>
> -int
> -as_compare(u_int8_t op, u_int32_t as, u_int32_t match, u_int32_t as_min,
> - u_int32_t as_max)
> -{
> - if ((op == OP_NONE || op == OP_EQ) && as == match)
> - return (1);
> - else if (op == OP_NE && as != match)
> - return (1);
> - else if (op == OP_RANGE && as >= as_min && as <= as_max)
> - return (1);
> - else if (op == OP_XRANGE && as > as_min && as < as_max)
> - return (1);
> - return (0);
> -}
> -
> /*
> * Extract the asnum out of the as segment at the specified position.
> * Direct access is not possible because of non-aligned reads.
> - * ATTENTION: no bounds checks are done.
> + * Only works on verified and 4byte ASN paths.
> */
> u_int32_t
> aspath_extract(const void *seg, int pos)
> @@ -397,6 +406,9 @@ aspath_extract(const void *seg, int pos)
> const u_char *ptr = seg;
> u_int32_t as;
>
> + /* minimal overflow check, return 0 since that is an invalid ASN */
> + if (pos >= ptr[1])
> + return (0);
> ptr += 2 + sizeof(u_int32_t) * pos;
> memcpy(&as, ptr, sizeof(u_int32_t));
> return (ntohl(as));
>
