T6962: frr: fix wrong kernel routes updates

scripts/package-build/frr/patches/frr/0007-zebra-remove-kernel-route-on-last-address-deletion.patch

@@ -0,0 +1,214 @@
+From 1ba7319656c548075e466a8ad1d068f7b1d66756 Mon Sep 17 00:00:00 2001
+From: Kyrylo Yatsenko <hedrok@gmail.com>
+Date: Thu, 11 Sep 2025 17:43:08 +0300
+Subject: [PATCH] zebra: remove kernel route on last address deletion
+
+Fixes issue #13561
+
+Linux kernel deletes IPv4 routes when last interface IPv4 address
+is deleted, but intentionally doesn't send RTM_DELROUTE in this case.
+
+FRR has function rib_update_handle_kernel_route_down_possibility
+that handles setting interface down, but not removal of last address.
+
+To fix the situation:
+
+* Add RIB_UPDATE_KERNEL_LAST_ADDRESS_DELETED to enum rib_update_event
+* In zebra_if_addr_update_ctx make more specific check that last
+  address is deleted and trigger RIB_UPDATE_KERNEL_LAST_ADDRESS_DELETED
+  instead of RIB_UPDATE_KERNEL in this case. If it was not last address,
+  don't emit any RIB_UPDATE.
+* Call rib_update_handle_kernel_route_down_possibility not only
+  for event RIB_UPDATE_INTERFACE_DOWN, but also for
+  RIB_UPDATE_KERNEL_LAST_ADDRESS_DELETED.
+* Change rib_update_handle_kernel_route_down_possibility not to
+  consider IPv4 route alive when interface is up, but there
+  are no IPv4 addresses left.
+
+Relevant kernel code:
+
+* net/ipv4/fib_frontend.c fib_inetaddr_event
+* net/ipv4/fib_semantics.c fib_sync_down_dev
+
+Comment from kernel networking author that RTM_DELROUTE isn't sent
+intentionally:
+
+https://bugzilla.kernel.org/show_bug.cgi?id=207089
+Signed-off-by: Kyrylo Yatsenko <hedrok@gmail.com>
+---
+ lib/if.c          | 12 +++++++++++
+ lib/if.h          |  1 +
+ zebra/interface.c |  8 ++++---
+ zebra/rib.h       |  1 +
+ zebra/zebra_rib.c | 55 +++++++++++++++++++++++++++++++++++++++--------
+ 5 files changed, 65 insertions(+), 12 deletions(-)
+
+diff --git a/lib/if.c b/lib/if.c
+index 8f15230f23..2402d17992 100644
+--- a/lib/if.c
++++ b/lib/if.c
+@@ -899,6 +899,18 @@ nbr_connected_log(struct nbr_connected *connected, char *str)
+ 	zlog_info("%s", logbuf);
+ }
+
++/* Return true if there is at least one connected address in the given family  */
++bool if_has_connected_with_family(struct interface *ifp, int family)
++{
++	struct connected *connected;
++
++	frr_each (if_connected, ifp->connected, connected)
++		if (connected->address->family == family)
++			return true;
++
++	return false;
++}
++
+ /* count the number of connected addresses that are in the given family */
+ unsigned int connected_count_by_family(struct interface *ifp, int family)
+ {
+diff --git a/lib/if.h b/lib/if.h
+index 0dc56bd210..233213ca84 100644
+--- a/lib/if.h
++++ b/lib/if.h
+@@ -606,6 +606,7 @@ extern struct connected *connected_lookup_prefix(struct interface *ifp,
+ 						 const struct prefix *p);
+ extern struct connected *connected_lookup_prefix_exact(struct interface *ifp,
+ 						       const struct prefix *p);
++extern bool if_has_connected_with_family(struct interface *ifp, int family);
+ extern unsigned int connected_count_by_family(struct interface *ifp, int family);
+ extern struct nbr_connected *nbr_connected_new(void);
+ extern void nbr_connected_free(struct nbr_connected *connected);
+diff --git a/zebra/interface.c b/zebra/interface.c
+index e2c2b4a80c..48343355ba 100644
+--- a/zebra/interface.c
++++ b/zebra/interface.c
+@@ -1313,11 +1313,13 @@ static void zebra_if_addr_update_ctx(struct zebra_dplane_ctx *ctx,
+ 	}
+
+ 	/*
+-	 * Linux kernel does not send route delete on interface down/addr del
++	 * Linux kernel does not send route delete on interface down/last addr del
+ 	 * so we have to re-process routes it owns (i.e. kernel routes)
++	 * See rib_update_handle_kernel_route_down_possibility for more details
+ 	 */
+-	if (op != DPLANE_OP_INTF_ADDR_ADD)
+-		rib_update(RIB_UPDATE_KERNEL);
++	if (op != DPLANE_OP_INTF_ADDR_ADD && addr->family == AF_INET &&
++	    !if_has_connected_with_family(ifp, AF_INET))
++		rib_update(RIB_UPDATE_KERNEL_LAST_ADDRESS_DELETED);
+ }
+
+ static void zebra_if_update_ctx(struct zebra_dplane_ctx *ctx,
+diff --git a/zebra/rib.h b/zebra/rib.h
+index 5fedb07335..2f1954de9d 100644
+--- a/zebra/rib.h
++++ b/zebra/rib.h
+@@ -330,6 +330,7 @@ enum rib_update_event {
+ 	RIB_UPDATE_KERNEL,
+ 	RIB_UPDATE_RMAP_CHANGE,
+ 	RIB_UPDATE_OTHER,
++	RIB_UPDATE_KERNEL_LAST_ADDRESS_DELETED,
+ 	RIB_UPDATE_MAX
+ };
+ void rib_update_finish(void);
+diff --git a/zebra/zebra_rib.c b/zebra/zebra_rib.c
+index 752f8282df..eaba976265 100644
+--- a/zebra/zebra_rib.c
++++ b/zebra/zebra_rib.c
+@@ -4465,6 +4465,9 @@ static const char *rib_update_event2str(enum rib_update_event event)
+ 	case RIB_UPDATE_OTHER:
+ 		ret = "RIB_UPDATE_OTHER";
+ 		break;
++	case RIB_UPDATE_KERNEL_LAST_ADDRESS_DELETED:
++		ret = "RIB_UPDATE_KERNEL_LAST_ADDRESS_DELETED";
++		break;
+ 	case RIB_UPDATE_MAX:
+ 		break;
+ 	}
+@@ -4487,13 +4490,45 @@ rib_update_handle_kernel_route_down_possibility(struct route_node *rn,
+ 	bool alive = false;
+
+ 	for (ALL_NEXTHOPS(re->nhe->nhg, nexthop)) {
++		if (!nexthop->ifindex || nexthop->type == NEXTHOP_TYPE_BLACKHOLE) {
++			/* blackhole nexthops have no interfaces */
++			alive = true;
++			break;
++		}
++
+ 		struct interface *ifp = if_lookup_by_index(nexthop->ifindex,
+ 							   nexthop->vrf_id);
+
+-		if ((ifp && if_is_up(ifp)) || nexthop->type == NEXTHOP_TYPE_BLACKHOLE) {
++		if (!ifp || !if_is_up(ifp)) {
++			/* interface is not up, not alive */
++			continue;
++		}
++
++		/*
++		 * Kernel deletes IPv4 routes from interface when last IPv4 address is deleted
++		 * It is not important whether nexthop is reachable after address
++		 * is deleted - route is deleted only after last address deletion.
++		 *
++		 * See net/ipv4/fib_frontend.c fib_inetaddr_event,
++		 * net/ipv4/fib_semantics.c fib_sync_down_dev
++		 */
++
++		/* If not IPv4, set alive
++		 * Check rn->p->family: for nexthop->type=NEXTHOP_TYPE_IFINDEX it
++		 * depends on destination only
++		 */
++		if (rn->p.family != AF_INET) {
+ 			alive = true;
+ 			break;
+ 		}
++
++		/* Check if there are any IPv4 addresses connected, if yes - set alive */
++		if (if_has_connected_with_family(ifp, AF_INET)) {
++			alive = true;
++			break;
++		}
++
++		/* Otherwise kernel deletes the route */
+ 	}
+
+ 	if (!alive) {
+@@ -4518,8 +4553,9 @@ static void rib_update_route_node(struct route_node *rn, int type,
+ 	bool re_changed = false;
+
+ 	RNODE_FOREACH_RE_SAFE (rn, re, next) {
+-		if (event == RIB_UPDATE_INTERFACE_DOWN && type == re->type &&
+-		    type == ZEBRA_ROUTE_KERNEL)
++		if ((event == RIB_UPDATE_INTERFACE_DOWN ||
++		     event == RIB_UPDATE_KERNEL_LAST_ADDRESS_DELETED) &&
++		    type == re->type && type == ZEBRA_ROUTE_KERNEL)
+ 			rib_update_handle_kernel_route_down_possibility(rn, re);
+ 		else if (type == ZEBRA_ROUTE_ALL || type == re->type) {
+ 			SET_FLAG(re->status, ROUTE_ENTRY_CHANGED);
+@@ -4562,17 +4598,18 @@ void rib_update_table(struct route_table *table, enum rib_update_event event,
+ 		 * If we are looking at a route node and the node
+ 		 * has already been queued  we don't
+ 		 * need to queue it up again, unless it is
+-		 * an interface down event as that we need
+-		 * to process this no matter what.
++		 * an interface down event or last address down event
++		 * as that we need
++		 * to process these no matter what.
+ 		 */
+-		if (rn->info &&
+-		    CHECK_FLAG(rib_dest_from_rnode(rn)->flags,
+-			       RIB_ROUTE_ANY_QUEUED) &&
+-		    event != RIB_UPDATE_INTERFACE_DOWN)
++		if (rn->info && CHECK_FLAG(rib_dest_from_rnode(rn)->flags, RIB_ROUTE_ANY_QUEUED) &&
++		    event != RIB_UPDATE_INTERFACE_DOWN &&
++		    event != RIB_UPDATE_KERNEL_LAST_ADDRESS_DELETED)
+ 			continue;
+
+ 		switch (event) {
+ 		case RIB_UPDATE_INTERFACE_DOWN:
++		case RIB_UPDATE_KERNEL_LAST_ADDRESS_DELETED:
+ 		case RIB_UPDATE_KERNEL:
+ 			rib_update_route_node(rn, ZEBRA_ROUTE_KERNEL, event);
+ 			break;
+-- 
+2.50.1
+