netdev - [Patch bpf-next v4 3/4] skmsg: get rid of skb

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Message-Id: <20220615162014.89193-4-xiyou.wangcong@gmail.com>
Date:   Wed, 15 Jun 2022 09:20:13 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     netdev@...r.kernel.org
Cc:     bpf@...r.kernel.org, Cong Wang <cong.wang@...edance.com>,
        Eric Dumazet <edumazet@...gle.com>,
        John Fastabend <john.fastabend@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jakub Sitnicki <jakub@...udflare.com>
Subject: [Patch bpf-next v4 3/4] skmsg: get rid of skb_clone()

From: Cong Wang <cong.wang@...edance.com>

With ->read_skb() now we have an entire skb dequeued from
receive queue, now we just need to grab an addtional refcnt
before passing its ownership to recv actors.

And we should not touch them any more, particularly for
skb->sk. Fortunately, skb->sk is already set for most of
the protocols except UDP where skb->sk has been stolen,
so we have to fix it up for UDP case.

Cc: Eric Dumazet <edumazet@...gle.com>
Cc: John Fastabend <john.fastabend@...il.com>
Cc: Daniel Borkmann <daniel@...earbox.net>
Cc: Jakub Sitnicki <jakub@...udflare.com>
Signed-off-by: Cong Wang <cong.wang@...edance.com>
---
 net/core/skmsg.c | 7 +------
 net/ipv4/udp.c   | 1 +
 2 files changed, 2 insertions(+), 6 deletions(-)

diff --git a/net/core/skmsg.c b/net/core/skmsg.c
index f7f63b7d990c..8b248d289c11 100644
--- a/net/core/skmsg.c
+++ b/net/core/skmsg.c
@@ -1167,10 +1167,7 @@ static int sk_psock_verdict_recv(struct sock *sk, struct sk_buff *skb)
 	int ret = __SK_DROP;
 	int len = skb->len;
 
-	/* clone here so sk_eat_skb() in tcp_read_sock does not drop our data */
-	skb = skb_clone(skb, GFP_ATOMIC);
-	if (!skb)
-		return 0;
+	skb_get(skb);
 
 	rcu_read_lock();
 	psock = sk_psock(sk);
@@ -1183,12 +1180,10 @@ static int sk_psock_verdict_recv(struct sock *sk, struct sk_buff *skb)
 	if (!prog)
 		prog = READ_ONCE(psock->progs.skb_verdict);
 	if (likely(prog)) {
-		skb->sk = sk;
 		skb_dst_drop(skb);
 		skb_bpf_redirect_clear(skb);
 		ret = bpf_prog_run_pin_on_cpu(prog, skb);
 		ret = sk_psock_map_verd(ret, skb_bpf_redirect_fetch(skb));
-		skb->sk = NULL;
 	}
 	if (sk_psock_verdict_apply(psock, skb, ret) < 0)
 		len = 0;
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 0a1e90b80e36..b09936ccf709 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1817,6 +1817,7 @@ int udp_read_skb(struct sock *sk, skb_read_actor_t recv_actor)
 			continue;
 		}
 
+		WARN_ON(!skb_set_owner_sk_safe(skb, sk));
 		used = recv_actor(sk, skb);
 		if (used <= 0) {
 			if (!copied)
-- 
2.34.1