sk_buff: drop all skb extensions on free and skb scrubbing

Now that we have a 3rd extension, add a new helper that drops the
extension space and use it when we need to scrub an sk_buff.

At this time, scrubbing clears secpath and bridge netfilter data, but
retains the tc skb extension, after this patch all three get cleared.

NAPI reuse/free assumes we can only have a secpath attached to skb, but
it seems better to clear all extensions there as well.

v2: add unlikely hint (Eric Dumazet)

Fixes: 95a7233c ("net: openvswitch: Set OvS recirc_id from tc chain index")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/skbuff.h

@@ -4144,8 +4144,17 @@ static inline void *skb_ext_find(const struct sk_buff *skb, enum skb_ext_id id)
 
 	return NULL;
 }
+
+static inline void skb_ext_reset(struct sk_buff *skb)
+{
+	if (unlikely(skb->active_extensions)) {
+		__skb_ext_put(skb->extensions);
+		skb->active_extensions = 0;
+	}
+}
 #else
 static inline void skb_ext_put(struct sk_buff *skb) {}
+static inline void skb_ext_reset(struct sk_buff *skb) {}
 static inline void skb_ext_del(struct sk_buff *skb, int unused) {}
 static inline void __skb_ext_copy(struct sk_buff *d, const struct sk_buff *s) {}
 static inline void skb_ext_copy(struct sk_buff *dst, const struct sk_buff *s) {}

net/core/dev.c

@@ -5666,7 +5666,7 @@ EXPORT_SYMBOL(gro_find_complete_by_type);
 static void napi_skb_free_stolen_head(struct sk_buff *skb)
 {
 	skb_dst_drop(skb);
-	secpath_reset(skb);
+	skb_ext_put(skb);
 	kmem_cache_free(skbuff_head_cache, skb);
 }
 
@@ -5733,7 +5733,7 @@ static void napi_reuse_skb(struct napi_struct *napi, struct sk_buff *skb)
 	skb->encapsulation = 0;
 	skb_shinfo(skb)->gso_type = 0;
 	skb->truesize = SKB_TRUESIZE(skb_end_offset(skb));
-	secpath_reset(skb);
+	skb_ext_reset(skb);
 
 	napi->skb = skb;
 }

net/core/skbuff.c

@@ -5119,7 +5119,7 @@ void skb_scrub_packet(struct sk_buff *skb, bool xnet)
 	skb->skb_iif = 0;
 	skb->ignore_df = 0;
 	skb_dst_drop(skb);
-	secpath_reset(skb);
+	skb_ext_reset(skb);
 	nf_reset(skb);
 	nf_reset_trace(skb);