bgpd: Fix for ain->attr corruption during path update

1. Consider a established L2VPN EVPN BGP peer with soft-reconfiguartion
   inbound configured

2. When the interface of this directly connected BGP peer is shutdown,
   bgp_soft_reconfig_table_update() is called, which memsets the evpn buffer
   and calls bgp_update() with received attributes stored in ain table(ain->attr).
   In bgp_update(), evpn_overlay attribute in ain->attr (which is an interned
   attr) was modified by doing a memcpy

3. Above action causes 2 attributes in the attrhash (which were previously different)
   to match!

4. Later during fsm change event of the peer, bgp_adj_in_remove() is called
   to clean up the ain->attr. But, because 2 attrs in attrhash match, it causes
   BGP to assert in bgp_attr_unintern()

Signed-off-by: Pooja Jagadeesh Doijode <[email protected]>

Author: Pdoijode

bgpd/bgp_route.c

@@ -4065,17 +4065,24 @@ void bgp_update(struct peer *peer, const struct prefix *p, uint32_t addpath_id,
 	if (has_valid_label)
 		assert(label != NULL);
 
-	/* Update overlay index of the attribute */
-	if (afi == AFI_L2VPN && evpn)
-		memcpy(&attr->evpn_overlay, evpn,
-		       sizeof(struct bgp_route_evpn));
 
 	/* When peer's soft reconfiguration enabled.  Record input packet in
 	   Adj-RIBs-In.  */
-	if (!soft_reconfig
-	    && CHECK_FLAG(peer->af_flags[afi][safi], PEER_FLAG_SOFT_RECONFIG)
-	    && peer != bgp->peer_self)
+	if (!soft_reconfig &&
+	    CHECK_FLAG(peer->af_flags[afi][safi], PEER_FLAG_SOFT_RECONFIG) &&
+	    peer != bgp->peer_self) {
+		/*
+		 * If the trigger is not from soft_reconfig and if
+		 * PEER_FLAG_SOFT_RECONFIG is enabled for the peer, then attr
+		 * will not be interned. In which case, it is ok to update the
+		 * attr->evpn_overlay, so that, this can be stored in adj_in.
+		 */
+		if ((afi == AFI_L2VPN) && evpn) {
+			memcpy(&attr->evpn_overlay, evpn,
+			       sizeof(struct bgp_route_evpn));
+		}
 		bgp_adj_in_set(dest, peer, attr, addpath_id);
+	}
 
 	/* Update permitted loop count */
 	if (CHECK_FLAG(peer->af_flags[afi][safi], PEER_FLAG_ALLOWAS_IN))
@@ -4203,6 +4210,15 @@ void bgp_update(struct peer *peer, const struct prefix *p, uint32_t addpath_id,
 		}
 
 	new_attr = *attr;
+	/*
+	 * If bgp_update is called with soft_reconfig set then
+	 * attr is interned. In this case, do not overwrite the
+	 * attr->evpn_overlay with evpn directly. Instead memcpy
+	 * evpn to new_atr.evpn_overlay before it is interned.
+	 */
+	if (soft_reconfig && (afi == AFI_L2VPN) && evpn)
+		memcpy(&new_attr.evpn_overlay, evpn,
+		       sizeof(struct bgp_route_evpn));
 
 	/* Apply incoming route-map.
 	 * NB: new_attr may now contain newly allocated values from route-map