Subject: Re: [PATCH bpf] bpf, sockmap: Reject sk_msg egress redirects to non-TCP sockets

From: Jakub Sitnicki <[email-masked]>
Date: Wed, 20 Sep 2023 22:59:58 +0200

On Wed, Sep 20, 2023 at 11:19 AM -07, Kui-Feng Lee wrote:
> On 9/20/23 03:20, Jakub Sitnicki wrote:
>> diff --git a/net/core/sock_map.c b/net/core/sock_map.c
>> index cb11750b1df5..4292c2ed1828 100644
>> --- a/net/core/sock_map.c
>> +++ b/net/core/sock_map.c
>> @@ -668,6 +668,8 @@ BPF_CALL_4(bpf_msg_redirect_map, struct sk_msg *, msg,
>>   	sk = __sock_map_lookup_elem(map, key);
>>   	if (unlikely(!sk || !sock_map_redirect_allowed(sk)))
>>   		return SK_DROP;
>> +	if (!(flags & BPF_F_INGRESS) && !sk_is_tcp(sk))
>> +		return SK_DROP;
>>     	msg->flags = flags;
>>   	msg->sk_redir = sk;
>> @@ -1267,6 +1269,8 @@ BPF_CALL_4(bpf_msg_redirect_hash, struct sk_msg *, msg,
>>   	sk = __sock_hash_lookup_elem(map, key);
>>   	if (unlikely(!sk || !sock_map_redirect_allowed(sk)))
>>   		return SK_DROP;
>> +	if (!(flags & BPF_F_INGRESS) && !sk_is_tcp(sk))
>> +		return SK_DROP;
>>     	msg->flags = flags;
>>   	msg->sk_redir = sk;
>
> Just be curious! Can it happen to other socket types?
> I mean to redirect a msg from a sk of any type to one of another type.

Today sk_msg redirects are implemented only for tcp4 and tcp6.

Here's a full matrix of what redirects are supported [1].

[1] https://gist.github.com/jsitnicki/578fdd614d181bed2b02922b17972b4e