Messages in this thread | | | Subject | Re: [PATCH net] tcp: avoid creating multiple req socks with the same tuples | From | maowenan <> | Date | Wed, 5 Jun 2019 10:06:38 +0800 |
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On 2019/6/4 23:24, Eric Dumazet wrote: > On Tue, Jun 4, 2019 at 7:47 AM Mao Wenan <maowenan@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 <maowenan@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?
> > 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) { + 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. > > . >
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