netdev - [PATCHv3 bpf-next 2/5] net: Track socket refcounts in skb_steal

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Message-Id: <20200327042556.11560-3-joe@wand.net.nz>
Date:   Thu, 26 Mar 2020 21:25:53 -0700
From:   Joe Stringer <joe@...d.net.nz>
To:     bpf@...r.kernel.org
Cc:     netdev@...r.kernel.org, daniel@...earbox.net, ast@...nel.org,
        eric.dumazet@...il.com, lmb@...udflare.com, kafai@...com
Subject: [PATCHv3 bpf-next 2/5] net: Track socket refcounts in skb_steal_sock()

Refactor the UDP/TCP handlers slightly to allow skb_steal_sock() to make
the determination of whether the socket is reference counted in the case
where it is prefetched by earlier logic such as early_demux or
dst_sk_prefetch.

Signed-off-by: Joe Stringer <joe@...d.net.nz>
---
v3: No changes
v2: Initial version
---
 include/net/inet6_hashtables.h |  3 +--
 include/net/inet_hashtables.h  |  3 +--
 include/net/sock.h             | 10 +++++++++-
 net/ipv4/udp.c                 |  6 ++++--
 net/ipv6/udp.c                 |  9 ++++++---
 5 files changed, 21 insertions(+), 10 deletions(-)

diff --git a/include/net/inet6_hashtables.h b/include/net/inet6_hashtables.h
index fe96bf247aac..81b965953036 100644
--- a/include/net/inet6_hashtables.h
+++ b/include/net/inet6_hashtables.h
@@ -85,9 +85,8 @@ static inline struct sock *__inet6_lookup_skb(struct inet_hashinfo *hashinfo,
 					      int iif, int sdif,
 					      bool *refcounted)
 {
-	struct sock *sk = skb_steal_sock(skb);
+	struct sock *sk = skb_steal_sock(skb, refcounted);
 
-	*refcounted = true;
 	if (sk)
 		return sk;
 
diff --git a/include/net/inet_hashtables.h b/include/net/inet_hashtables.h
index d0019d3395cf..ad64ba6a057f 100644
--- a/include/net/inet_hashtables.h
+++ b/include/net/inet_hashtables.h
@@ -379,10 +379,9 @@ static inline struct sock *__inet_lookup_skb(struct inet_hashinfo *hashinfo,
 					     const int sdif,
 					     bool *refcounted)
 {
-	struct sock *sk = skb_steal_sock(skb);
+	struct sock *sk = skb_steal_sock(skb, refcounted);
 	const struct iphdr *iph = ip_hdr(skb);
 
-	*refcounted = true;
 	if (sk)
 		return sk;
 
diff --git a/include/net/sock.h b/include/net/sock.h
index 2613d21a667a..1ca2e808cb8e 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -2533,15 +2533,23 @@ skb_sk_is_prefetched(struct sk_buff *skb)
 	return skb->destructor == sock_pfree;
 }
 
-static inline struct sock *skb_steal_sock(struct sk_buff *skb)
+/**
+ * skb_steal_sock
+ * @skb to steal the socket from
+ * @refcounted is set to true if the socket is reference-counted
+ */
+static inline struct sock *
+skb_steal_sock(struct sk_buff *skb, bool *refcounted)
 {
 	if (skb->sk) {
 		struct sock *sk = skb->sk;
 
+		*refcounted = true;
 		skb->destructor = NULL;
 		skb->sk = NULL;
 		return sk;
 	}
+	*refcounted = false;
 	return NULL;
 }
 
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 2633fc231593..b4035021bbd3 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -2288,6 +2288,7 @@ int __udp4_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
 	struct rtable *rt = skb_rtable(skb);
 	__be32 saddr, daddr;
 	struct net *net = dev_net(skb->dev);
+	bool refcounted;
 
 	/*
 	 *  Validate the packet.
@@ -2313,7 +2314,7 @@ int __udp4_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
 	if (udp4_csum_init(skb, uh, proto))
 		goto csum_error;
 
-	sk = skb_steal_sock(skb);
+	sk = skb_steal_sock(skb, &refcounted);
 	if (sk) {
 		struct dst_entry *dst = skb_dst(skb);
 		int ret;
@@ -2322,7 +2323,8 @@ int __udp4_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
 			udp_sk_rx_dst_set(sk, dst);
 
 		ret = udp_unicast_rcv_skb(sk, skb, uh);
-		sock_put(sk);
+		if (refcounted)
+			sock_put(sk);
 		return ret;
 	}
 
diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
index 5dc439a391fe..7d4151747340 100644
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -843,6 +843,7 @@ int __udp6_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
 	struct net *net = dev_net(skb->dev);
 	struct udphdr *uh;
 	struct sock *sk;
+	bool refcounted;
 	u32 ulen = 0;
 
 	if (!pskb_may_pull(skb, sizeof(struct udphdr)))
@@ -879,7 +880,7 @@ int __udp6_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
 		goto csum_error;
 
 	/* Check if the socket is already available, e.g. due to early demux */
-	sk = skb_steal_sock(skb);
+	sk = skb_steal_sock(skb, &refcounted);
 	if (sk) {
 		struct dst_entry *dst = skb_dst(skb);
 		int ret;
@@ -888,12 +889,14 @@ int __udp6_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
 			udp6_sk_rx_dst_set(sk, dst);
 
 		if (!uh->check && !udp_sk(sk)->no_check6_rx) {
-			sock_put(sk);
+			if (refcounted)
+				sock_put(sk);
 			goto report_csum_error;
 		}
 
 		ret = udp6_unicast_rcv_skb(sk, skb, uh);
-		sock_put(sk);
+		if (refcounted)
+			sock_put(sk);
 		return ret;
 	}
 
-- 
2.20.1