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Better profylaction recursive route loops

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In some specific configurations, it was possible to send BIRD into an
infinite loop of recursive next hop resolution. This was caused by route
priority inversion.

To prevent priority inversions affecting other next hops, we simply
refuse to resolve any next hop if the best route for the matching prefix
is recursive or any other route with the same preference is recursive.

Next hop resolution doesn't change route priority, therefore it is
perfectly OK to resolve BGP next hops e.g. by an OSPF route, yet if the
same (or covering) prefix is also announced by iBGP, by retraction of
the OSPF route we would get a possible priority inversion.
This commit is contained in:
Maria Matejka 2021-10-22 19:43:55 +02:00
parent d2c1036a42
commit 71b3456eed
1 changed files with 5 additions and 2 deletions
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7
nest/rt-table.c
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@ -3529,9 +3529,10 @@ rt_update_hostentry(rtable *tab, struct hostentry *he)
{ {
rte *e = n->routes; rte *e = n->routes;
rta *a = e->attrs; rta *a = e->attrs;
pxlen = n->n.addr->pxlen; word pref = a->pref;
if (a->hostentry) for (rte *ee = n->routes; ee; ee = ee->next)
if ((ee->attrs->pref >= pref) && ee->attrs->hostentry)
{ {
/* Recursive route should not depend on another recursive route */ /* Recursive route should not depend on another recursive route */
log(L_WARN "Next hop address %I resolvable through recursive route for %N", log(L_WARN "Next hop address %I resolvable through recursive route for %N",
@ -3539,6 +3540,8 @@ rt_update_hostentry(rtable *tab, struct hostentry *he)
goto done; goto done;
} }
pxlen = n->n.addr->pxlen;
if (a->dest == RTD_UNICAST) if (a->dest == RTD_UNICAST)
{ {
for (struct nexthop *nh = &(a->nh); nh; nh = nh->next) for (struct nexthop *nh = &(a->nh); nh; nh = nh->next)