netfilter: nf_dup_netdev: add nf_dev_xmit_recursion*() helpers and use them

Update nft_dup and nft_fwd to use the nf_dev_xmit_recursion() helpers.
This patch also disables BH when transmitting the skb to address a
possible migration to different CPU leading to imbalanced decrementation
of the recursion counters.

This is modeled after Florian Westphal's dev_xmit_recursion*() API
available since commit 97cdcf37b57e ("net: place xmit recursion in
softnet data") according to its current state in the tree.

Fixes: 1d47b55b36d2 ("netfilter: nft_fwd_netdev: use recursion counter in neigh egress path")
Fixes: f37ad9127039 ("netfilter: nf_dup_netdev: Move the recursion counter struct netdev_xmit")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 29 insertions, 5 deletions

diff --git a/include/net/netfilter/nf_dup_netdev.h b/include/net/netfilter/nf_dup_netdev.h
index 609bcf422a9b..f6b05bd80c3f 100644
--- a/include/net/netfilter/nf_dup_netdev.h
+++ b/include/net/netfilter/nf_dup_netdev.h
@@ -11,15 +11,39 @@ void nf_fwd_netdev_egress(const struct nft_pktinfo *pkt, int oif);
 
 #define NF_RECURSION_LIMIT	2
 
-static inline u8 *nf_get_nf_dup_skb_recursion(void)
-{
 #ifndef CONFIG_PREEMPT_RT
-	return this_cpu_ptr(&softnet_data.xmit.nf_dup_skb_recursion);
+static inline bool nf_dev_xmit_recursion(void)
+{
+	return unlikely(__this_cpu_read(softnet_data.xmit.nf_dup_skb_recursion) >
+			NF_RECURSION_LIMIT);
+}
+
+static inline void nf_dev_xmit_recursion_inc(void)
+{
+	__this_cpu_inc(softnet_data.xmit.nf_dup_skb_recursion);
+}
+
+static inline void nf_dev_xmit_recursion_dec(void)
+{
+	__this_cpu_dec(softnet_data.xmit.nf_dup_skb_recursion);
+}
 #else
-	return &current->net_xmit.nf_dup_skb_recursion;
-#endif
+static inline bool nf_dev_xmit_recursion(void)
+{
+	return unlikely(current->net_xmit.nf_dup_skb_recursion > NF_RECURSION_LIMIT);
+}
+
+static inline void nf_dev_xmit_recursion_inc(void)
+{
+	current->net_xmit.nf_dup_skb_recursion++;
 }
 
+static inline void nf_dev_xmit_recursion_dec(void)
+{
+	current->net_xmit.nf_dup_skb_recursion--;
+}
+#endif
+
 struct nft_offload_ctx;
 struct nft_flow_rule;