netdev - [Patch bpf-next] tcp: fix sock skb accounting in tcp_read

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Message-Id: <20220709222029.297471-1-xiyou.wangcong@gmail.com>
Date:   Sat,  9 Jul 2022 15:20:29 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     netdev@...r.kernel.org
Cc:     bpf@...r.kernel.org, Cong Wang <cong.wang@...edance.com>,
        syzbot+a0e6f8738b58f7654417@...kaller.appspotmail.com,
        Stanislav Fomichev <sdf@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        John Fastabend <john.fastabend@...il.com>
Subject: [Patch bpf-next] tcp: fix sock skb accounting in tcp_read_skb()

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

Before commit 965b57b469a5 ("net: Introduce a new proto_ops
->read_skb()"), skb was not dequeued from receive queue hence
when we close TCP socket skb can be just flushed synchronously.

After this commit, we have to uncharge skb immediately after being
dequeued, otherwise it is still charged in the original sock. And we
still need to retain skb->sk, as eBPF programs may extract sock
information from skb->sk. Therefore, we have to call
skb_set_owner_sk_safe() here.

Fixes: 965b57b469a5 ("net: Introduce a new proto_ops ->read_skb()")
Reported-and-tested-by: syzbot+a0e6f8738b58f7654417@...kaller.appspotmail.com
Tested-by: Stanislav Fomichev <sdf@...gle.com>
Cc: Eric Dumazet <edumazet@...gle.com>
Cc: John Fastabend <john.fastabend@...il.com>
Signed-off-by: Cong Wang <cong.wang@...edance.com>
---
 net/ipv4/tcp.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 9d2fd3ced21b..c6b1effb2afd 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1749,6 +1749,7 @@ int tcp_read_skb(struct sock *sk, skb_read_actor_t recv_actor)
 		int used;
 
 		__skb_unlink(skb, &sk->sk_receive_queue);
+		WARN_ON(!skb_set_owner_sk_safe(skb, sk));
 		used = recv_actor(sk, skb);
 		if (used <= 0) {
 			if (!copied)
-- 
2.34.1