On Sun, Jul 10, 2022 at 12:20 AM Cong Wang <xiyou.wangcong@xxxxxxxxx> wrote:
>
> From: Cong Wang <cong.wang@xxxxxxxxxxxxx>
>
> 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@xxxxxxxxxxxxxxxxxxxxxxxxx
> Tested-by: Stanislav Fomichev <sdf@xxxxxxxxxx>
> Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
> Cc: John Fastabend <john.fastabend@xxxxxxxxx>
> Signed-off-by: Cong Wang <cong.wang@xxxxxxxxxxxxx>
> ---
> 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
>
I am reading tcp_read_skb(),it seems to have other bugs.
I wonder why syzbot has not caught up yet.
It ignores the offset value from tcp_recv_skb(), this looks wrong to me.
The reason tcp_read_sock() passes a @len parameter is that is it not
skb->len, but (skb->len - offset)
Also if recv_actor(sk, skb) returns 0, we probably still need to
advance tp->copied_seq,
for instance if skb had a pure FIN (and thus skb->len == 0), since you
removed the skb from sk_receive_queue ?
