netfilter: bridge: add support for pppoe filtering

stable inclusion
from linux-4.19.226
commit 519f563eca1b89965dd406a8f9807ca76562d202

--------------------------------

[ Upstream commit 28b78ecf ]

This makes 'bridge-nf-filter-pppoe-tagged' sysctl work for
bridged traffic.

Looking at the original commit it doesn't appear this ever worked:

 static unsigned int br_nf_post_routing(unsigned int hook, struct sk_buff **pskb,
[..]
        if (skb->protocol == htons(ETH_P_8021Q)) {
                skb_pull(skb, VLAN_HLEN);
                skb->network_header += VLAN_HLEN;
+       } else if (skb->protocol == htons(ETH_P_PPP_SES)) {
+               skb_pull(skb, PPPOE_SES_HLEN);
+               skb->network_header += PPPOE_SES_HLEN;
        }
 [..]
	NF_HOOK(... POST_ROUTING, ...)

... but the adjusted offsets are never restored.

The alternative would be to rip this code out for good,
but otoh we'd have to keep this anyway for the vlan handling
(which works because vlan tag info is in the skb, not the packet
 payload).
Reported-and-tested-by: NAmish Chana <amish@3g.co.za>
Fixes: 516299d2 ("[NETFILTER]: bridge-nf: filter bridged IPv4/IPv6 encapsulated in pppoe traffic")
Signed-off-by: NFlorian Westphal <fw@strlen.de>
Signed-off-by: NPablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NYongqiang Liu <liuyongqiang13@huawei.com>
Signed-off-by: NLaibin Qiu <qiulaibin@huawei.com>
Signed-off-by: NYongqiang Liu <liuyongqiang13@huawei.com>

net/bridge/br_netfilter_hooks.c

@@ -727,6 +727,9 @@ static int br_nf_dev_queue_xmit(struct net *net, struct sock *sk, struct sk_buff
 	if (nf_bridge->frag_max_size && nf_bridge->frag_max_size < mtu)
 		mtu = nf_bridge->frag_max_size;
 
+	nf_bridge_update_protocol(skb);
+	nf_bridge_push_encap_header(skb);
+
 	if (skb_is_gso(skb) || skb->len + mtu_reserved <= mtu) {
 		nf_bridge_info_free(skb);
 		return br_dev_queue_push_xmit(net, sk, skb);
@@ -744,8 +747,6 @@ static int br_nf_dev_queue_xmit(struct net *net, struct sock *sk, struct sk_buff
 
 		IPCB(skb)->frag_max_size = nf_bridge->frag_max_size;
 
-		nf_bridge_update_protocol(skb);
-
 		data = this_cpu_ptr(&brnf_frag_data_storage);
 
 		data->vlan_tci = skb->vlan_tci;
@@ -768,8 +769,6 @@ static int br_nf_dev_queue_xmit(struct net *net, struct sock *sk, struct sk_buff
 
 		IP6CB(skb)->frag_max_size = nf_bridge->frag_max_size;
 
-		nf_bridge_update_protocol(skb);
-
 		data = this_cpu_ptr(&brnf_frag_data_storage);
 		data->encap_size = nf_bridge_encap_header_len(skb);
 		data->size = ETH_HLEN + data->encap_size;