netdev - [PATCH net 2/2] net: fix a memleak when uncloning an skb dst and its metadata

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Date:   Wed,  2 Feb 2022 12:01:37 +0100
From:   Antoine Tenart <atenart@...nel.org>
To:     davem@...emloft.net, kuba@...nel.org
Cc:     Antoine Tenart <atenart@...nel.org>, netdev@...r.kernel.org,
        vladbu@...dia.com, pabeni@...hat.com, pshelar@....org
Subject: [PATCH net 2/2] net: fix a memleak when uncloning an skb dst and its metadata

When uncloning an skb dst and its associated metadata, a new
dst+metadata is allocated and later replaces the old one in the skb.
This is helpful to have a non-shared dst+metadata attached to a specific
skb.

The issue is the uncloned dst+metadata is initialized with a refcount of
1, which is increased to 2 before attaching it to the skb. When
tun_dst_unclone returns, the dst+metadata is only referenced from a
single place (the skb) while its refcount is 2. Its refcount will never
drop to 0 (when the skb is consumed), leading to a memory leak.

Fix this by removing the call to dst_hold in tun_dst_unclone, as the
dst+metadata refcount is already 1.

Fixes: fc4099f17240 ("openvswitch: Fix egress tunnel info.")
Cc: Pravin B Shelar <pshelar@....org>
Reported-by: Vlad Buslov <vladbu@...dia.com>
Tested-by: Vlad Buslov <vladbu@...dia.com>
Signed-off-by: Antoine Tenart <atenart@...nel.org>
---
 include/net/dst_metadata.h | 1 -
 1 file changed, 1 deletion(-)

diff --git a/include/net/dst_metadata.h b/include/net/dst_metadata.h
index c8f8b7b56bba..edd75c89222d 100644
--- a/include/net/dst_metadata.h
+++ b/include/net/dst_metadata.h
@@ -135,7 +135,6 @@ static inline struct metadata_dst *tun_dst_unclone(struct sk_buff *skb)
 #endif

 	skb_dst_drop(skb);
-	dst_hold(&new_md->dst);
 	skb_dst_set(skb, &new_md->dst);
 	return new_md;
 }
-- 
2.34.1