netdev - [PATCH net v2 1/2] skbuff: skb_clone_sk_optional(): add function to always clone a skb and increase refcount on sk if valid

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Date:   Tue, 23 Feb 2021 06:53:19 +0100
From:   Oleksij Rempel <o.rempel@...gutronix.de>
To:     mkl@...gutronix.de, "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Oliver Hartkopp <socketcan@...tkopp.net>,
        Robin van der Gracht <robin@...tonic.nl>,
        Johannes Berg <johannes@...solutions.net>
Cc:     Oleksij Rempel <o.rempel@...gutronix.de>, kernel@...gutronix.de,
        linux-can@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
        linux-wireless@...r.kernel.org
Subject: [PATCH net v2 1/2] skbuff: skb_clone_sk_optional(): add function to always clone a skb and increase refcount on sk if valid

There already the function skb_clone_sk(), which clones the skb, but
only if the sk is valid.

There are several users in the networking stack, which always need a
clone of a skb with the sk refcount incremented (but only if the sk is
valid). This patch adds such a function.

Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
---
 include/linux/skbuff.h |  1 +
 net/core/skbuff.c      | 27 +++++++++++++++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 6d0a33d1c0db..99d552017508 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -3874,6 +3874,7 @@ static inline void skb_metadata_clear(struct sk_buff *skb)
 	skb_metadata_set(skb, 0);
 }
 
+struct sk_buff *skb_clone_sk_optional(struct sk_buff *skb);
 struct sk_buff *skb_clone_sk(struct sk_buff *skb);
 
 #ifdef CONFIG_NETWORK_PHY_TIMESTAMPING
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 545a472273a5..97341f173fb0 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -4671,6 +4671,33 @@ struct sk_buff *sock_dequeue_err_skb(struct sock *sk)
 }
 EXPORT_SYMBOL(sock_dequeue_err_skb);
 
+/**
+ * skb_clone_sk_optional - create clone of skb, and take reference to socket if
+ *                         socket is referenced in original skb
+ * @skb: the skb to clone
+ *
+ * This function always creates a clone of a buffer. If it that holds a valid
+ * reference on sk_refcnt this is increased.
+ */
+struct sk_buff *skb_clone_sk_optional(struct sk_buff *skb)
+{
+	struct sock *sk = skb->sk;
+	struct sk_buff *clone;
+
+	clone = skb_clone(skb, GFP_ATOMIC);
+	if (!clone)
+		return NULL;
+
+	if (!sk || !refcount_inc_not_zero(&sk->sk_refcnt))
+		return clone;
+
+	clone->sk = sk;
+	clone->destructor = sock_efree;
+
+	return clone;
+}
+EXPORT_SYMBOL(skb_clone_sk_optional);
+
 /**
  * skb_clone_sk - create clone of skb, and take reference to socket
  * @skb: the skb to clone
-- 
2.29.2