[PATCH v2] netfilter: nf_flowtable: move dst_check to packet path

[Ritaro Takenaka <ritarot634@xxxxxxxxx>]

Fixes sporadic IPv6 packet loss when flow offloading is enabled.

IPv6 route GC and flowtable GC are not synchronized.
When dst_cache becomes stale and a packet passes through the flow before
the flowtable GC teardowns it, the packet can be dropped.

So, it is necessary to check dst every time in packet path.

Signed-off-by: Ritaro Takenaka <ritarot634@xxxxxxxxx>
---
 net/netfilter/nf_flow_table_core.c | 23 +----------------------
 net/netfilter/nf_flow_table_ip.c   | 17 +++++++++++++++++
 2 files changed, 18 insertions(+), 22 deletions(-)

diff --git a/net/netfilter/nf_flow_table_core.c b/net/netfilter/nf_flow_table_core.c
index 3db256da919b..1d99afaf22c1 100644
--- a/net/netfilter/nf_flow_table_core.c
+++ b/net/netfilter/nf_flow_table_core.c
@@ -438,32 +438,11 @@ nf_flow_table_iterate(struct nf_flowtable *flow_table,
 	return err;
 }
 
-static bool flow_offload_stale_dst(struct flow_offload_tuple *tuple)
-{
-	struct dst_entry *dst;
-
-	if (tuple->xmit_type == FLOW_OFFLOAD_XMIT_NEIGH ||
-	    tuple->xmit_type == FLOW_OFFLOAD_XMIT_XFRM) {
-		dst = tuple->dst_cache;
-		if (!dst_check(dst, tuple->dst_cookie))
-			return true;
-	}
-
-	return false;
-}
-
-static bool nf_flow_has_stale_dst(struct flow_offload *flow)
-{
-	return flow_offload_stale_dst(&flow->tuplehash[FLOW_OFFLOAD_DIR_ORIGINAL].tuple) ||
-	       flow_offload_stale_dst(&flow->tuplehash[FLOW_OFFLOAD_DIR_REPLY].tuple);
-}
-
 static void nf_flow_offload_gc_step(struct nf_flowtable *flow_table,
 				    struct flow_offload *flow, void *data)
 {
 	if (nf_flow_has_expired(flow) ||
-	    nf_ct_is_dying(flow->ct) ||
-	    nf_flow_has_stale_dst(flow))
+	    nf_ct_is_dying(flow->ct))
 		set_bit(NF_FLOW_TEARDOWN, &flow->flags);
 
 	if (test_bit(NF_FLOW_TEARDOWN, &flow->flags)) {
diff --git a/net/netfilter/nf_flow_table_ip.c b/net/netfilter/nf_flow_table_ip.c
index 32c0eb1b4821..402742dd054c 100644
--- a/net/netfilter/nf_flow_table_ip.c
+++ b/net/netfilter/nf_flow_table_ip.c
@@ -367,6 +367,14 @@ nf_flow_offload_ip_hook(void *priv, struct sk_buff *skb,
 	if (nf_flow_state_check(flow, iph->protocol, skb, thoff))
 		return NF_ACCEPT;
 
+	if (tuplehash->tuple.xmit_type == FLOW_OFFLOAD_XMIT_NEIGH ||
+	    tuplehash->tuple.xmit_type == FLOW_OFFLOAD_XMIT_XFRM) {
+		if (!dst_check(tuplehash->tuple.dst_cache, 0)) {
+			flow_offload_teardown(flow);
+			return NF_ACCEPT;
+		}
+	}
+
 	if (skb_try_make_writable(skb, thoff + hdrsize))
 		return NF_DROP;
 
@@ -624,6 +632,15 @@ nf_flow_offload_ipv6_hook(void *priv, struct sk_buff *skb,
 	if (nf_flow_state_check(flow, ip6h->nexthdr, skb, thoff))
 		return NF_ACCEPT;
 
+	if (tuplehash->tuple.xmit_type == FLOW_OFFLOAD_XMIT_NEIGH ||
+	    tuplehash->tuple.xmit_type == FLOW_OFFLOAD_XMIT_XFRM) {
+		if (!dst_check(tuplehash->tuple.dst_cache,
+			       tuplehash->tuple.dst_cookie)) {
+			flow_offload_teardown(flow);
+			return NF_ACCEPT;
+		}
+	}
+
 	if (skb_try_make_writable(skb, thoff + hdrsize))
 		return NF_DROP;
 
-- 
2.34.1