From: Jakub Sitnicki <jakub@cloudflare.com>
To: Martin Lau <kafai@fb.com>
Cc: "bpf\@vger.kernel.org" <bpf@vger.kernel.org>,
"netdev\@vger.kernel.org" <netdev@vger.kernel.org>,
"kernel-team\@cloudflare.com" <kernel-team@cloudflare.com>,
John Fastabend <john.fastabend@gmail.com>
Subject: Re: [PATCH bpf-next 4/8] bpf, sockmap: Don't let child socket inherit psock or its ops on copy
Date: Tue, 26 Nov 2019 16:54:33 +0100 [thread overview]
Message-ID: <87ftiaocp2.fsf@cloudflare.com> (raw)
In-Reply-To: <20191125223845.6t6xoqcwcqxuqbdf@kafai-mbp>
On Mon, Nov 25, 2019 at 11:38 PM CET, Martin Lau wrote:
> On Sat, Nov 23, 2019 at 12:07:47PM +0100, Jakub Sitnicki wrote:
> [ ... ]
>
>> @@ -370,6 +378,11 @@ static inline void sk_psock_restore_proto(struct sock *sk,
>> sk->sk_prot = psock->sk_proto;
>> psock->sk_proto = NULL;
>> }
>> +
>> + if (psock->icsk_af_ops) {
>> + icsk->icsk_af_ops = psock->icsk_af_ops;
>> + psock->icsk_af_ops = NULL;
>> + }
>> }
>
> [ ... ]
>
>> +static struct sock *tcp_bpf_syn_recv_sock(const struct sock *sk,
>> + struct sk_buff *skb,
>> + struct request_sock *req,
>> + struct dst_entry *dst,
>> + struct request_sock *req_unhash,
>> + bool *own_req)
>> +{
>> + const struct inet_connection_sock_af_ops *ops;
>> + void (*write_space)(struct sock *sk);
>> + struct sk_psock *psock;
>> + struct proto *proto;
>> + struct sock *child;
>> +
>> + rcu_read_lock();
>> + psock = sk_psock(sk);
>> + if (likely(psock)) {
>> + proto = psock->sk_proto;
>> + write_space = psock->saved_write_space;
>> + ops = psock->icsk_af_ops;
> It is not immediately clear to me what ensure
> ops is not NULL here.
>
> It is likely I missed something. A short comment would
> be very useful here.
I can see the readability problem. Looking at it now, perhaps it should
be rewritten, to the same effect, as:
static struct sock *tcp_bpf_syn_recv_sock(...)
{
const struct inet_connection_sock_af_ops *ops = NULL;
...
rcu_read_lock();
psock = sk_psock(sk);
if (likely(psock)) {
proto = psock->sk_proto;
write_space = psock->saved_write_space;
ops = psock->icsk_af_ops;
}
rcu_read_unlock();
if (!ops)
ops = inet_csk(sk)->icsk_af_ops;
child = ops->syn_recv_sock(sk, skb, req, dst, req_unhash, own_req);
If psock->icsk_af_ops were NULL, it would mean we haven't initialized it
properly. To double check what happens here:
In sock_map_link we do a setup dance where we first create the psock and
later initialize the socket callbacks (tcp_bpf_init).
static int sock_map_link(struct bpf_map *map, struct sk_psock_progs *progs,
struct sock *sk)
{
...
if (psock) {
...
} else {
psock = sk_psock_init(sk, map->numa_node);
if (!psock) {
ret = -ENOMEM;
goto out_progs;
}
sk_psock_is_new = true;
}
...
if (sk_psock_is_new) {
ret = tcp_bpf_init(sk);
if (ret < 0)
goto out_drop;
} else {
tcp_bpf_reinit(sk);
}
The "if (sk_psock_new)" branch triggers the call chain that leads to
saving & overriding socket callbacks.
tcp_bpf_init -> tcp_bpf_update_sk_prot -> sk_psock_update_proto
Among them, icsk_af_ops.
static inline void sk_psock_update_proto(...)
{
...
psock->icsk_af_ops = icsk->icsk_af_ops;
icsk->icsk_af_ops = af_ops;
}
Goes without saying that a comment is needed.
Thanks for the feedback,
Jakub
next prev parent reply other threads:[~2019-11-26 15:54 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-23 11:07 [PATCH bpf-next 0/8] Extend SOCKMAP to store listening sockets Jakub Sitnicki
2019-11-23 11:07 ` [PATCH bpf-next 1/8] bpf, sockmap: Return socket cookie on lookup from syscall Jakub Sitnicki
2019-11-24 5:32 ` John Fastabend
2019-11-23 11:07 ` [PATCH bpf-next 2/8] bpf, sockmap: Let all kernel-land lookup values in SOCKMAP Jakub Sitnicki
2019-11-24 5:35 ` John Fastabend
2019-11-23 11:07 ` [PATCH bpf-next 3/8] bpf, sockmap: Allow inserting listening TCP sockets into SOCKMAP Jakub Sitnicki
2019-11-24 5:38 ` John Fastabend
2019-11-23 11:07 ` [PATCH bpf-next 4/8] bpf, sockmap: Don't let child socket inherit psock or its ops on copy Jakub Sitnicki
2019-11-24 5:56 ` John Fastabend
2019-11-25 22:38 ` Martin Lau
2019-11-26 15:54 ` Jakub Sitnicki [this message]
2019-11-26 17:16 ` Martin Lau
2019-11-26 18:36 ` Jakub Sitnicki
[not found] ` <87sglsfdda.fsf@cloudflare.com>
2019-12-11 17:20 ` Martin Lau
2019-12-12 11:27 ` Jakub Sitnicki
2019-12-12 19:23 ` Martin Lau
2019-12-17 15:06 ` Jakub Sitnicki
2019-11-26 18:43 ` John Fastabend
2019-11-27 22:18 ` Jakub Sitnicki
2019-11-23 11:07 ` [PATCH bpf-next 5/8] bpf: Allow selecting reuseport socket from a SOCKMAP Jakub Sitnicki
2019-11-24 5:57 ` John Fastabend
2019-11-25 1:24 ` Alexei Starovoitov
2019-11-25 4:17 ` John Fastabend
2019-11-25 10:40 ` Jakub Sitnicki
2019-11-25 22:07 ` Martin Lau
2019-11-26 14:30 ` Jakub Sitnicki
2019-11-26 19:03 ` Martin Lau
2019-11-27 21:34 ` Jakub Sitnicki
2019-11-23 11:07 ` [PATCH bpf-next 6/8] libbpf: Recognize SK_REUSEPORT programs from section name Jakub Sitnicki
2019-11-24 5:57 ` John Fastabend
2019-11-23 11:07 ` [PATCH bpf-next 7/8] selftests/bpf: Extend SK_REUSEPORT tests to cover SOCKMAP Jakub Sitnicki
2019-11-24 6:00 ` John Fastabend
2019-11-25 22:30 ` Martin Lau
2019-11-26 14:32 ` Jakub Sitnicki
2019-12-12 10:30 ` Jakub Sitnicki
2019-11-23 11:07 ` [PATCH bpf-next 8/8] selftests/bpf: Tests for SOCKMAP holding listening sockets Jakub Sitnicki
2019-11-24 6:04 ` John Fastabend
2019-11-24 6:10 ` [PATCH bpf-next 0/8] Extend SOCKMAP to store " John Fastabend
2019-11-25 9:22 ` Jakub Sitnicki
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