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[net-next,0/3] mptcp: reject invalid mp_join requests right away

Message ID 20201130153631.21872-1-fw@strlen.de
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Series mptcp: reject invalid mp_join requests right away | expand

Message

Florian Westphal Nov. 30, 2020, 3:36 p.m. UTC 
At the moment MPTCP can detect an invalid join request (invalid token,
max number of subflows reached, and so on) right away but cannot reject
the connection until the 3WHS has completed.
Instead the connection will complete and the subflow is reset afterwards.

To send the reset most information is already available, but we don't have
good spot where the reset could be sent:

1. The ->init_req callback is too early and also doesn't allow to return an
   error that could be used to inform the TCP stack that the SYN should be
   dropped.

2. The ->route_req callback lacks the skb needed to send a reset.

3. The ->send_synack callback is the best fit from the available hooks,
   but its called after the request socket has been inserted into the queue
   already. This means we'd have to remove it again right away.