From: Jakub Sitnicki <jakub@cloudflare•com>
To: Eric Dumazet <eric.dumazet@gmail•com>,
John Fastabend <john.fastabend@gmail•com>
Cc: bpf@vger•kernel.org, netdev@vger•kernel.org,
kernel-team@cloudflare•com,
John Fastabend <john.fastabend@gmail•com>,
Lorenz Bauer <lmb@cloudflare•com>, Martin Lau <kafai@fb•com>
Subject: Re: [PATCH bpf-next v4 02/12] net, sk_msg: Annotate lockless access to sk_prot on clone
Date: Thu, 23 Jan 2020 19:56:53 +0100 [thread overview]
Message-ID: <874kwm2e8a.fsf@cloudflare.com> (raw)
In-Reply-To: <a6bf279e-a998-84ab-4371-cd6c1ccbca5d@gmail.com>
On Thu, Jan 23, 2020 at 06:18 PM CET, Eric Dumazet wrote:
> On 1/23/20 7:55 AM, Jakub Sitnicki wrote:
>> sk_msg and ULP frameworks override protocol callbacks pointer in
>> sk->sk_prot, while tcp accesses it locklessly when cloning the listening
>> socket, that is with neither sk_lock nor sk_callback_lock held.
>>
>> Once we enable use of listening sockets with sockmap (and hence sk_msg),
>> there will be shared access to sk->sk_prot if socket is getting cloned
>> while being inserted/deleted to/from the sockmap from another CPU:
>>
>> Read side:
>>
>> tcp_v4_rcv
>> sk = __inet_lookup_skb(...)
>> tcp_check_req(sk)
>> inet_csk(sk)->icsk_af_ops->syn_recv_sock
>> tcp_v4_syn_recv_sock
>> tcp_create_openreq_child
>> inet_csk_clone_lock
>> sk_clone_lock
>> READ_ONCE(sk->sk_prot)
>>
>> Write side:
>>
>> sock_map_ops->map_update_elem
>> sock_map_update_elem
>> sock_map_update_common
>> sock_map_link_no_progs
>> tcp_bpf_init
>> tcp_bpf_update_sk_prot
>> sk_psock_update_proto
>> WRITE_ONCE(sk->sk_prot, ops)
>>
>> sock_map_ops->map_delete_elem
>> sock_map_delete_elem
>> __sock_map_delete
>> sock_map_unref
>> sk_psock_put
>> sk_psock_drop
>> sk_psock_restore_proto
>> tcp_update_ulp
>> WRITE_ONCE(sk->sk_prot, proto)
>>
>> Mark the shared access with READ_ONCE/WRITE_ONCE annotations.
>>
>> Acked-by: Martin KaFai Lau <kafai@fb•com>
>> Signed-off-by: Jakub Sitnicki <jakub@cloudflare•com>
>> ---
>> include/linux/skmsg.h | 3 ++-
>> net/core/sock.c | 5 +++--
>> net/ipv4/tcp_bpf.c | 4 +++-
>> net/ipv4/tcp_ulp.c | 3 ++-
>> net/tls/tls_main.c | 3 ++-
>> 5 files changed, 12 insertions(+), 6 deletions(-)
>>
>> diff --git a/include/linux/skmsg.h b/include/linux/skmsg.h
>> index 41ea1258d15e..55c834a5c25e 100644
>> --- a/include/linux/skmsg.h
>> +++ b/include/linux/skmsg.h
>> @@ -352,7 +352,8 @@ static inline void sk_psock_update_proto(struct sock *sk,
>> psock->saved_write_space = sk->sk_write_space;
>>
>> psock->sk_proto = sk->sk_prot;
>> - sk->sk_prot = ops;
>> + /* Pairs with lockless read in sk_clone_lock() */
>> + WRITE_ONCE(sk->sk_prot, ops);
>
>
> Note there are dozens of calls like
>
> if (sk->sk_prot->handler)
> sk->sk_prot->handler(...);
>
> Some of them being done lockless.
>
> I know it is painful, but presumably we need
>
> const struct proto *ops = READ_ONCE(sk->sk_prot);
>
> if (ops->handler)
> ops->handler(....);
Yikes! That will be quite an audit. Thank you for taking a look.
Now I think I understand what John had in mind when asking for pushing
these annotations to the bpf tree as well [0].
Considering these are lacking today, can I do it as a follow up?
[0] https://lore.kernel.org/bpf/20200110105027.257877-1-jakub@cloudflare.com/T/#m6a4f84a922a393719a7ea7b33dafdb6c66b72827
next prev parent reply other threads:[~2020-01-23 18:56 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-23 15:55 [PATCH bpf-next v4 00/12] Extend SOCKMAP to store listening sockets Jakub Sitnicki
2020-01-23 15:55 ` [PATCH bpf-next v4 01/12] bpf, sk_msg: Don't clear saved sock proto on restore Jakub Sitnicki
2020-01-23 15:55 ` [PATCH bpf-next v4 02/12] net, sk_msg: Annotate lockless access to sk_prot on clone Jakub Sitnicki
2020-01-23 17:18 ` Eric Dumazet
2020-01-23 18:56 ` Jakub Sitnicki [this message]
2020-01-23 19:15 ` John Fastabend
2020-01-27 9:36 ` Jakub Sitnicki
2020-01-23 15:55 ` [PATCH bpf-next v4 03/12] net, sk_msg: Clear sk_user_data pointer on clone if tagged Jakub Sitnicki
2020-01-23 15:55 ` [PATCH bpf-next v4 04/12] tcp_bpf: Don't let child socket inherit parent protocol ops on copy Jakub Sitnicki
2020-01-23 15:55 ` [PATCH bpf-next v4 05/12] bpf, sockmap: Allow inserting listening TCP sockets into sockmap Jakub Sitnicki
2020-01-23 15:55 ` [PATCH bpf-next v4 06/12] bpf, sockmap: Don't set up sockmap progs for listening sockets Jakub Sitnicki
2020-01-23 15:55 ` [PATCH bpf-next v4 07/12] bpf, sockmap: Return socket cookie on lookup from syscall Jakub Sitnicki
2020-01-23 15:55 ` [PATCH bpf-next v4 08/12] bpf, sockmap: Let all kernel-land lookup values in SOCKMAP Jakub Sitnicki
2020-01-23 15:55 ` [PATCH bpf-next v4 09/12] bpf: Allow selecting reuseport socket from a SOCKMAP Jakub Sitnicki
2020-01-23 15:55 ` [PATCH bpf-next v4 10/12] net: Generate reuseport group ID on group creation Jakub Sitnicki
2020-01-23 17:02 ` Martin Lau
2020-01-23 15:55 ` [PATCH bpf-next v4 11/12] selftests/bpf: Extend SK_REUSEPORT tests to cover SOCKMAP Jakub Sitnicki
2020-01-23 15:55 ` [PATCH bpf-next v4 12/12] selftests/bpf: Tests for SOCKMAP holding listening sockets Jakub Sitnicki
2020-01-27 11:13 ` [PATCH bpf-next v4 00/12] Extend SOCKMAP to store " Daniel Borkmann
2020-01-27 13:03 ` Jakub Sitnicki
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