Re: [Patch net v3 1/4] tcp: fix sock skb accounting in tcp_read_skb()

Jakub Sitnicki
2022-08-24T08:18:12Z

On Wed, Aug 17, 2022 at 12:54 PM -07, Cong Wang wrote:
> From: Cong Wang <cong.wang@bytedance.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@syzkaller.appspotmail.com
> Tested-by: Stanislav Fomichev <sdf@google.com>
> Cc: Eric Dumazet <edumazet@google.com>
> Cc: John Fastabend <john.fastabend@gmail.com>
> Cc: Jakub Sitnicki <jakub@cloudflare.com>
> Signed-off-by: Cong Wang <cong.wang@bytedance.com>
> ---
> net/ipv4/tcp.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index 970e9a2cca4a..05da5cac080b 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -1760,6 +1760,7 @@ 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)

That is a frequent operation.

Don't we want WARN_ON_ONCE like in tcp_read_sock?