+From: Pablo Neira Ayuso <pablo@netfilter.org>
+Date: Thu, 11 Apr 2024 13:28:59 +0200
+Subject: [PATCH] netfilter: flowtable: validate pppoe header
+
+Ensure there is sufficient room to access the protocol field of the
+PPPoe header. Validate it once before the flowtable lookup, then use a
+helper function to access protocol field.
+
+Reported-by: syzbot+b6f07e1c07ef40199081@syzkaller.appspotmail.com
+Fixes: 72efd585f714 ("netfilter: flowtable: add pppoe support")
+Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
+---
+
+--- a/include/net/netfilter/nf_flow_table.h
++++ b/include/net/netfilter/nf_flow_table.h
+@@ -335,7 +335,7 @@ int nf_flow_rule_route_ipv6(struct net *
+ int nf_flow_table_offload_init(void);
+ void nf_flow_table_offload_exit(void);
+
+-static inline __be16 nf_flow_pppoe_proto(const struct sk_buff *skb)
++static inline __be16 __nf_flow_pppoe_proto(const struct sk_buff *skb)
+ {
+ __be16 proto;
+
+@@ -351,6 +351,16 @@ static inline __be16 nf_flow_pppoe_proto
+ return 0;
+ }
+
++static inline bool nf_flow_pppoe_proto(struct sk_buff *skb, __be16 *inner_proto)
++{
++ if (!pskb_may_pull(skb, PPPOE_SES_HLEN))
++ return false;
++
++ *inner_proto = __nf_flow_pppoe_proto(skb);
++
++ return true;
++}
++
+ #define NF_FLOW_TABLE_STAT_INC(net, count) __this_cpu_inc((net)->ft.stat->count)
+ #define NF_FLOW_TABLE_STAT_DEC(net, count) __this_cpu_dec((net)->ft.stat->count)
+ #define NF_FLOW_TABLE_STAT_INC_ATOMIC(net, count) \
+--- a/net/netfilter/nf_flow_table_inet.c
++++ b/net/netfilter/nf_flow_table_inet.c
+@@ -21,7 +21,8 @@ nf_flow_offload_inet_hook(void *priv, st
+ proto = veth->h_vlan_encapsulated_proto;
+ break;
+ case htons(ETH_P_PPP_SES):
+- proto = nf_flow_pppoe_proto(skb);
++ if (!nf_flow_pppoe_proto(skb, &proto))
++ return NF_ACCEPT;
+ break;
+ default:
+ proto = skb->protocol;
+--- a/net/netfilter/nf_flow_table_ip.c
++++ b/net/netfilter/nf_flow_table_ip.c
+@@ -267,10 +267,11 @@ static unsigned int nf_flow_xmit_xfrm(st
+ return NF_STOLEN;
+ }
+
+-static bool nf_flow_skb_encap_protocol(const struct sk_buff *skb, __be16 proto,
++static bool nf_flow_skb_encap_protocol(struct sk_buff *skb, __be16 proto,
+ u32 *offset)
+ {
+ struct vlan_ethhdr *veth;
++ __be16 inner_proto;
+
+ switch (skb->protocol) {
+ case htons(ETH_P_8021Q):
+@@ -281,7 +282,8 @@ static bool nf_flow_skb_encap_protocol(c
+ }
+ break;
+ case htons(ETH_P_PPP_SES):
+- if (nf_flow_pppoe_proto(skb) == proto) {
++ if (nf_flow_pppoe_proto(skb, &inner_proto) &&
++ inner_proto == proto) {
+ *offset += PPPOE_SES_HLEN;
+ return true;
+ }
+@@ -310,7 +312,7 @@ static void nf_flow_encap_pop(struct sk_
+ skb_reset_network_header(skb);
+ break;
+ case htons(ETH_P_PPP_SES):
+- skb->protocol = nf_flow_pppoe_proto(skb);
++ skb->protocol = __nf_flow_pppoe_proto(skb);
+ skb_pull(skb, PPPOE_SES_HLEN);
+ skb_reset_network_header(skb);
+ break;