bgpd: fix hardset l3vpn label available in mpls pool

Today, when configuring BGP L3VPN mpls, the operator may
use that command to hardset a label value:

> router bgp 65500 vrf vrf1
> address-family ipv4 unicast
> label vpn export <hardset_label_value>

Today, BGP uses this value without checks, leading to potential
conflicts with other control planes like LDP. For instance, if
LDP initiates with a label chunk of [16;72] and BGP also uses the
50 label value, a conflict arises.

The 'label manager' service in zebra oversees label allocations.
While all the control plane daemons use it, BGP doesn't when a
hardset label is in place.

This update fixes this problem. Now, when a hardset label is set for
l3vpn export, a request is made to the label manager for approval,
ensuring no conflicts with other daemons. But, this means some existing
BGP configurations might become non-operational if they conflict with
labels already allocated to another daemon but not used.

note: Labels below 16 are reserved and won't be checked for consistency
by the label manager.

Fixes: ddb5b4880ba8 ("bgpd: vpn-vrf route leaking")
Signed-off-by: Philippe Guibert <philippe.guibert@6wind.com>

1 files changed, 12 insertions, 2 deletions

diff --git a/bgpd/bgp_zebra.c b/bgpd/bgp_zebra.c
index 212b7f398..e53416044 100644
--- a/bgpd/bgp_zebra.c
+++ b/bgpd/bgp_zebra.c
@@ -3423,6 +3423,9 @@ static bool bgp_zebra_label_manager_connect(void)
 	/* tell label pool that zebra is connected */
 	bgp_lp_event_zebra_up();
 
+	/* tell BGP L3VPN that label manager is available */
+	if (bgp_get_default())
+		vpn_leak_postchange_all();
 	return true;
 }
 
@@ -3921,7 +3924,8 @@ void bgp_zebra_send_nexthop_label(int cmd, mpls_label_t label,
 	zebra_send_mpls_labels(zclient, cmd, &zl);
 }
 
-bool bgp_zebra_request_label_range(uint32_t base, uint32_t chunk_size)
+bool bgp_zebra_request_label_range(uint32_t base, uint32_t chunk_size,
+				   bool label_auto)
 {
 	int ret;
 	uint32_t start, end;
@@ -3943,7 +3947,13 @@ bool bgp_zebra_request_label_range(uint32_t base, uint32_t chunk_size)
 		return false;
 	}
 
-	bgp_lp_event_chunk(start, end);
+	if (label_auto)
+		/* label automatic is serviced by the bgp label pool
+		 * manager, which allocates label chunks in
+		 * pre-pools, and which needs to be notified about
+		 * new chunks availability
+		 */
+		bgp_lp_event_chunk(start, end);
 
 	return true;
 }