On Tue, Jun 4, 2019 at 7:07 PM maowenan <maowe...@huawei.com> wrote: > > > > On 2019/6/4 23:24, Eric Dumazet wrote: > > On Tue, Jun 4, 2019 at 7:47 AM Mao Wenan <maowe...@huawei.com> wrote: > >> > >> There is one issue about bonding mode BOND_MODE_BROADCAST, and > >> two slaves with diffierent affinity, so packets will be handled > >> by different cpu. These are two pre-conditions in this case. > >> > >> When two slaves receive the same syn packets at the same time, > >> two request sock(reqsk) will be created if below situation happens: > >> 1. syn1 arrived tcp_conn_request, create reqsk1 and have not yet called > >> inet_csk_reqsk_queue_hash_add. > >> 2. syn2 arrived tcp_v4_rcv, it goes to tcp_conn_request and create reqsk2 > >> because it can't find reqsk1 in the __inet_lookup_skb. > >> > >> Then reqsk1 and reqsk2 are added to establish hash table, and two synack > >> with different > >> seq(seq1 and seq2) are sent to client, then tcp ack arrived and will be > >> processed in tcp_v4_rcv and tcp_check_req, if __inet_lookup_skb find the > >> reqsk2, and > >> tcp ack packet is ack_seq is seq1, it will be failed after checking: > >> TCP_SKB_CB(skb)->ack_seq != tcp_rsk(req)->snt_isn + 1) > >> and then tcp rst will be sent to client and close the connection. > >> > >> To fix this, do lookup before calling inet_csk_reqsk_queue_hash_add > >> to add reqsk2 to hash table, if it finds the existed reqsk1 with the same > >> five tuples, > >> it removes reqsk2 and does not send synack to client. > >> > >> Signed-off-by: Mao Wenan <maowe...@huawei.com> > >> --- > >> net/ipv4/tcp_input.c | 9 +++++++++ > >> 1 file changed, 9 insertions(+) > >> > >> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c > >> index 08a477e74cf3..c75eeb1fe098 100644 > >> --- a/net/ipv4/tcp_input.c > >> +++ b/net/ipv4/tcp_input.c > >> @@ -6569,6 +6569,15 @@ int tcp_conn_request(struct request_sock_ops > >> *rsk_ops, > >> bh_unlock_sock(fastopen_sk); > >> sock_put(fastopen_sk); > >> } else { > >> + struct sock *sk1 = req_to_sk(req); > >> + struct sock *sk2 = NULL; > >> + sk2 = __inet_lookup_established(sock_net(sk1), > >> &tcp_hashinfo, > >> + > >> sk1->sk_daddr, sk1->sk_dport, > >> + > >> sk1->sk_rcv_saddr, sk1->sk_num, > >> + > >> inet_iif(skb),inet_sdif(skb)); > >> + if (sk2 != NULL) > >> + goto drop_and_release; > >> + > >> tcp_rsk(req)->tfo_listener = false; > >> if (!want_cookie) > >> inet_csk_reqsk_queue_hash_add(sk, req, > > > > This issue has been discussed last year. > Can you share discussion information?
https://www.spinics.net/lists/netdev/msg507423.html > > > > > I am afraid your patch does not solve all races. > > > > The lookup you add is lockless, so this is racy. > it's right, it has already in race region. > > > > Really the only way to solve this is to make sure that _when_ the > > bucket lock is held, > > we do not insert a request socket if the 4-tuple is already in the > > chain (probably in inet_ehash_insert()) > > > > put lookup code in spin_lock() of inet_ehash_insert(), is it ok like this? > will it affect performance? > > in inet_ehash_insert(): > ... > spin_lock(lock); > + reqsk = __inet_lookup_established(sock_net(sk), &tcp_hashinfo, > + sk->sk_daddr, > sk->sk_dport, > + sk->sk_rcv_saddr, > sk->sk_num, > + sk_bound_dev_if, > sk_bound_dev_if); > + if (reqsk) { You should test this before asking :) > + spin_unlock(lock); > + return ret; > + } > + > if (osk) { > WARN_ON_ONCE(sk->sk_hash != osk->sk_hash); > ret = sk_nulls_del_node_init_rcu(osk); > } > if (ret) > __sk_nulls_add_node_rcu(sk, list); > spin_unlock(lock); > ... > > > This needs more tricky changes than your patch. > > > > . > > >