netfilter: nft_flow_offload: fix interaction with vrf slave device

In the forward chain, the iif is changed from slave device to master vrf
device. Thus, flow offload does not find a match on the lower slave
device.

This patch uses the cached route, ie. dst->dev, to update the iif and
oif fields in the flow entry.

After this patch, the following example works fine:

 # ip addr add dev eth0 1.1.1.1/24
 # ip addr add dev eth1 10.0.0.1/24
 # ip link add user1 type vrf table 1
 # ip l set user1 up
 # ip l set dev eth0 master user1
 # ip l set dev eth1 master user1

 # nft add table firewall
 # nft add flowtable f fb1 { hook ingress priority 0 \; devices = { eth0, eth1 } \; }
 # nft add chain f ftb-all {type filter hook forward priority 0 \; policy accept \; }
 # nft add rule f ftb-all ct zone 1 ip protocol tcp flow offload @fb1
 # nft add rule f ftb-all ct zone 1 ip protocol udp flow offload @fb1

Signed-off-by: wenxu <wenxu@ucloud.cn>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/net/netfilter/nf_flow_table.h

@@ -84,7 +84,6 @@ struct flow_offload {
 struct nf_flow_route {
 	struct {
 		struct dst_entry	*dst;
-		int			ifindex;
 	} tuple[FLOW_OFFLOAD_DIR_MAX];
 };
 

net/netfilter/nf_flow_table_core.c

@@ -28,6 +28,7 @@ flow_offload_fill_dir(struct flow_offload *flow, struct nf_conn *ct,
 {
 	struct flow_offload_tuple *ft = &flow->tuplehash[dir].tuple;
 	struct nf_conntrack_tuple *ctt = &ct->tuplehash[dir].tuple;
+	struct dst_entry *other_dst = route->tuple[!dir].dst;
 	struct dst_entry *dst = route->tuple[dir].dst;
 
 	ft->dir = dir;
@@ -50,8 +51,8 @@ flow_offload_fill_dir(struct flow_offload *flow, struct nf_conn *ct,
 	ft->src_port = ctt->src.u.tcp.port;
 	ft->dst_port = ctt->dst.u.tcp.port;
 
-	ft->iifidx = route->tuple[dir].ifindex;
-	ft->oifidx = route->tuple[!dir].ifindex;
+	ft->iifidx = other_dst->dev->ifindex;
+	ft->oifidx = dst->dev->ifindex;
 	ft->dst_cache = dst;
 }
 

net/netfilter/nft_flow_offload.c

@@ -30,9 +30,11 @@ static int nft_flow_route(const struct nft_pktinfo *pkt,
 	switch (nft_pf(pkt)) {
 	case NFPROTO_IPV4:
 		fl.u.ip4.daddr = ct->tuplehash[dir].tuple.src.u3.ip;
+		fl.u.ip4.flowi4_oif = nft_in(pkt)->ifindex;
 		break;
 	case NFPROTO_IPV6:
 		fl.u.ip6.daddr = ct->tuplehash[dir].tuple.src.u3.in6;
+		fl.u.ip6.flowi6_oif = nft_in(pkt)->ifindex;
 		break;
 	}
 
@@ -41,9 +43,7 @@ static int nft_flow_route(const struct nft_pktinfo *pkt,
 		return -ENOENT;
 
 	route->tuple[dir].dst		= this_dst;
-	route->tuple[dir].ifindex	= nft_in(pkt)->ifindex;
 	route->tuple[!dir].dst		= other_dst;
-	route->tuple[!dir].ifindex	= nft_out(pkt)->ifindex;
 
 	return 0;
 }