[PATCH net-next 2/2] net: Make skb_ext_put_mctp() idempotent

[Jakub Sitnicki <jakub@cloudflare.com>]

The MCTP flow extension can be released either when it is deleted from an
skb or when the last skb holding the extension block is freed. Handle the
release in __skb_ext_del(), which is currently missing, and make
skb_ext_put_mctp() safe to call from both paths.

This will let __skb_ext_put() release the MCTP key without checking whether
the extension is present first, which is needed if we want to reuse skb_ext
chunks area after skb scrubbing.

Suggested-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
---
 net/core/skbuff.c | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index aa8b42c74f42..ab195b99c853 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -7248,8 +7248,11 @@ static void skb_ext_put_sp(struct sec_path *sp)
 #ifdef CONFIG_MCTP_FLOWS
 static void skb_ext_put_mctp(struct mctp_flow *flow)
 {
-	if (flow->key)
-		mctp_key_unref(flow->key);
+	if (!flow->key)
+		return;
+
+	mctp_key_unref(flow->key);
+	flow->key = NULL;
 }
 #endif
 
@@ -7261,13 +7264,20 @@ void __skb_ext_del(struct sk_buff *skb, enum skb_ext_id id)
 	if (skb->active_extensions == 0) {
 		skb->extensions = NULL;
 		__skb_ext_put(ext);
-#ifdef CONFIG_XFRM
-	} else if (id == SKB_EXT_SEC_PATH &&
-		   refcount_read(&ext->refcnt) == 1) {
+		return;
+	}
+
+	if (refcount_read(&ext->refcnt) > 1)
+		return;
 
+#ifdef CONFIG_XFRM
+	if (id == SKB_EXT_SEC_PATH)
 		skb_ext_put_sp(skb_ext_get_ptr(ext, SKB_EXT_SEC_PATH));
 #endif
-	}
+#ifdef CONFIG_MCTP_FLOWS
+	if (id == SKB_EXT_MCTP)
+		skb_ext_put_mctp(skb_ext_get_ptr(ext, SKB_EXT_MCTP));
+#endif
 }
 EXPORT_SYMBOL(__skb_ext_del);
 

-- 
2.43.0