From e3d901f8638dec32eac4c2690912138963ae5a05 Mon Sep 17 00:00:00 2001
From: Mark Stapp <mjs@voltanet.io>
Date: Tue, 11 May 2021 15:57:39 -0400
Subject: [PATCH] lib,zebra: Use a flag to track down status for connected
 addrs

Track 'down' state of connected addresses with a new flag. We
may have multiple addresses on an interface that share a prefix;
in those cases, we need to determine when the first address
is valid, to install a connected route, and similarly detect
when the last address goes 'down', to remove the connected
route.

Signed-off-by: Mark Stapp <mjs@voltanet.io>
---
 lib/if.h          |  3 +++
 zebra/connected.c | 28 +++++++++++++++++++++++-----
 2 files changed, 26 insertions(+), 5 deletions(-)

diff --git a/lib/if.h b/lib/if.h
index f425ba8bce..0d689fe14b 100644
--- a/lib/if.h
+++ b/lib/if.h
@@ -393,6 +393,7 @@ struct connected {
 #define ZEBRA_IFC_REAL         (1 << 0)
 #define ZEBRA_IFC_CONFIGURED   (1 << 1)
 #define ZEBRA_IFC_QUEUED       (1 << 2)
+#define ZEBRA_IFC_DOWN         (1 << 3)
 	/*
 	   The ZEBRA_IFC_REAL flag should be set if and only if this address
 	   exists in the kernel and is actually usable. (A case where it exists
@@ -406,6 +407,8 @@ struct connected {
 	   in the kernel. It may and should be set although the address might
 	   not be
 	   usable yet. (compare with ZEBRA_IFC_REAL)
+	   The ZEBRA_IFC_DOWN flag is used to record that an address is
+	   present, but down/unavailable.
 	 */
 
 	/* Flags for connected address. */
diff --git a/zebra/connected.c b/zebra/connected.c
index 1e03f8b639..883334d509 100644
--- a/zebra/connected.c
+++ b/zebra/connected.c
@@ -38,7 +38,6 @@
 #include "zebra/connected.h"
 #include "zebra/rtadv.h"
 #include "zebra/zebra_mpls.h"
-#include "zebra/debug.h"
 #include "zebra/zebra_errors.h"
 #include "zebra/zebra_router.h"
 
@@ -223,6 +222,9 @@ void connected_up(struct interface *ifp, struct connected *ifc)
 	if (!CHECK_FLAG(ifc->conf, ZEBRA_IFC_REAL))
 		return;
 
+	/* Ensure 'down' flag is cleared */
+	UNSET_FLAG(ifc->conf, ZEBRA_IFC_DOWN);
+
 	PREFIX_COPY(&p, CONNECTED_PREFIX(ifc));
 
 	/* Apply mask to the network. */
@@ -280,7 +282,8 @@ void connected_up(struct interface *ifp, struct connected *ifc)
 		PREFIX_COPY(&cp, CONNECTED_PREFIX(c));
 		apply_mask(&cp);
 
-		if (prefix_same(&cp, &p))
+		if (prefix_same(&cp, &p) &&
+		    !CHECK_FLAG(c->conf, ZEBRA_IFC_DOWN))
 			count++;
 
 		if (count >= 2)
@@ -390,7 +393,7 @@ void connected_down(struct interface *ifp, struct connected *ifc)
 	if (!zvrf) {
 		flog_err(
 			EC_ZEBRA_VRF_NOT_FOUND,
-			"%s: Received Up for interface but no associated zvrf: %d",
+			"%s: Received Down for interface but no associated zvrf: %d",
 			__func__, ifp->vrf_id);
 		return;
 	}
@@ -398,6 +401,17 @@ void connected_down(struct interface *ifp, struct connected *ifc)
 	if (!CHECK_FLAG(ifc->conf, ZEBRA_IFC_REAL))
 		return;
 
+	/* Skip if we've already done this; this can happen if we have a
+	 * config change that takes an interface down, then we receive kernel
+	 * notifications about the downed interface and its addresses.
+	 */
+	if (CHECK_FLAG(ifc->conf, ZEBRA_IFC_DOWN)) {
+		if (IS_ZEBRA_DEBUG_RIB)
+			zlog_debug("%s: ifc %p, %pFX already DOWN",
+				   __func__, ifc, ifc->address);
+		return;
+	}
+
 	PREFIX_COPY(&p, CONNECTED_PREFIX(ifc));
 
 	/* Apply mask to the network. */
@@ -423,6 +437,9 @@ void connected_down(struct interface *ifp, struct connected *ifc)
 		break;
 	}
 
+	/* Mark the address as 'down' */
+	SET_FLAG(ifc->conf, ZEBRA_IFC_DOWN);
+
 	/*
 	 * It's possible to have X number of addresses
 	 * on a interface that all resolve to the same
@@ -436,10 +453,11 @@ void connected_down(struct interface *ifp, struct connected *ifc)
 		PREFIX_COPY(&cp, CONNECTED_PREFIX(c));
 		apply_mask(&cp);
 
-		if (prefix_same(&p, &cp))
+		if (prefix_same(&p, &cp) &&
+		    !CHECK_FLAG(c->conf, ZEBRA_IFC_DOWN))
 			count++;
 
-		if (count >= 2)
+		if (count >= 1)
 			return;
 	}