Subject: Re: [PATCH bpf-next v2 05/11] bpf, sockmap: Allow inserting listening TCP sockets into sockmap

From: Jakub Sitnicki <[email-masked]>
Date: Mon, 13 Jan 2020 16:48:46 +0100

On Sun, Jan 12, 2020 at 12:59 AM CET, John Fastabend wrote:
> Jakub Sitnicki wrote:
>> In order for sockmap type to become a generic collection for storing TCP
>> sockets we need to loosen the checks during map update, while tightening
>> the checks in redirect helpers.
>>
>> Currently sockmap requires the TCP socket to be in established state (or
>> transitioning out of SYN_RECV into established state when done from BPF),
>> which prevents inserting listening sockets.
>>
>> Change the update pre-checks so that the socket can also be in listening
>> state. If the state is not white-listed, return -EINVAL to be consistent
>> with REUSEPORT_SOCKARRY map type.
>>
>> Since it doesn't make sense to redirect with sockmap to listening sockets,
>> add appropriate socket state checks to BPF redirect helpers too.
>>
>> Signed-off-by: Jakub Sitnicki <[email-masked]>
>> ---
>>  net/core/sock_map.c                     | 46 ++++++++++++++++++++-----
>>  tools/testing/selftests/bpf/test_maps.c |  6 +---
>>  2 files changed, 39 insertions(+), 13 deletions(-)
>>
>> diff --git a/net/core/sock_map.c b/net/core/sock_map.c
>> index eb114ee419b6..99daea502508 100644
>> --- a/net/core/sock_map.c
>> +++ b/net/core/sock_map.c
>> @@ -396,6 +396,23 @@ static bool sock_map_sk_is_suitable(const struct sock *sk)
>>  	       sk->sk_protocol == IPPROTO_TCP;
>>  }
>>
>> +/* Is sock in a state that allows inserting into the map?
>> + * SYN_RECV is needed for updates on BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB.
>> + */
>> +static bool sock_map_update_okay(const struct sock *sk)
>> +{
>> +	return (1 << sk->sk_state) & (TCPF_ESTABLISHED |
>> +				      TCPF_SYN_RECV |
>> +				      TCPF_LISTEN);
>> +}
>> +
>> +/* Is sock in a state that allows redirecting into it? */
>> +static bool sock_map_redirect_okay(const struct sock *sk)
>> +{
>> +	return (1 << sk->sk_state) & (TCPF_ESTABLISHED |
>> +				      TCPF_SYN_RECV);
>> +}
>> +
>>  static int sock_map_update_elem(struct bpf_map *map, void *key,
>>  				void *value, u64 flags)
>>  {
>> @@ -413,11 +430,14 @@ static int sock_map_update_elem(struct bpf_map *map, void *key,
>>  		ret = -EINVAL;
>>  		goto out;
>>  	}
>> -	if (!sock_map_sk_is_suitable(sk) ||
>> -	    sk->sk_state != TCP_ESTABLISHED) {
>> +	if (!sock_map_sk_is_suitable(sk)) {
>>  		ret = -EOPNOTSUPP;
>>  		goto out;
>>  	}
>> +	if (!sock_map_update_okay(sk)) {
>> +		ret = -EINVAL;
>> +		goto out;
>> +	}
>
> I nit but seeing we need a v3 anyways. How about consolidating
> this state checks into sock_map_sk_is_suitable() so we don't have
> multiple if branches or this '|| TCP_ESTABLISHED' like we do now.

Ah, I see the pattern now :-)

>>
>>  	sock_map_sk_acquire(sk);
>>  	ret = sock_map_update_common(map, idx, sk, flags);
>> @@ -433,6 +453,7 @@ BPF_CALL_4(bpf_sock_map_update, struct bpf_sock_ops_kern *, sops,
>>  	WARN_ON_ONCE(!rcu_read_lock_held());
>>
>>  	if (likely(sock_map_sk_is_suitable(sops->sk) &&
>> +		   sock_map_update_okay(sops->sk) &&
>>  		   sock_map_op_okay(sops)))
>>  		return sock_map_update_common(map, *(u32 *)key, sops->sk,
>>  					      flags);
>> @@ -454,13 +475,17 @@ BPF_CALL_4(bpf_sk_redirect_map, struct sk_buff *, skb,
>>  	   struct bpf_map *, map, u32, key, u64, flags)
>>  {
>>  	struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
>> +	struct sock *sk;
>>
>>  	if (unlikely(flags & ~(BPF_F_INGRESS)))
>>  		return SK_DROP;
>> -	tcb->bpf.flags = flags;
>> -	tcb->bpf.sk_redir = __sock_map_lookup_elem(map, key);
>> -	if (!tcb->bpf.sk_redir)
>> +
>> +	sk = __sock_map_lookup_elem(map, key);
>> +	if (!sk || !sock_map_redirect_okay(sk))
>>  		return SK_DROP;
>
> unlikely(!sock_map_redirect_okay)? Or perhaps unlikely the entire case,
> if (unlikely(!sk || !sock_map_redirect_okay(sk)). I think users should
> know if the sk is a valid sock or not and this is just catching the
> error case. Any opinion?
>
> Otherwise looks good.

Both ideas SGTM. Will incorporate into next version. Thanks!

-jkbs