netdev - [Patch bpf-next v1 3/4] skmsg: get rid of skb

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Date:   Sun, 10 Apr 2022 09:10:41 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     netdev@...r.kernel.org
Cc:     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 v1 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 19bca36940a2..7aa37b6287e1 100644
--- a/net/core/skmsg.c
+++ b/net/core/skmsg.c
@@ -1162,10 +1162,7 @@ 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);
@@ -1178,12 +1175,10 @@ 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 9faca5758ed6..dbf33f68555d 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1818,6 +1818,7 @@ 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)
-- 
2.32.0