Re: [PATCH net-next v2 2/4] net: psp: require an established connection for association setup

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

Daniel Zahka wrote:
> Check sk_state under the socket lock in both the rx-assoc and tx-assoc
> handlers, and only allow association setup on sockets in
> TCP_ESTABLISHED. Also, fail connect() when PSP assoc state is already
> present, and remove the dead PSP MSS adjustment from
> tcp_v[46]_connect().
> 
> The net effect of this commit is:
> 1. PSP assoc state can never exist on a listen socket.
> 2. The upgrade to PSP must be done while the socket is in
>    TCP_ESTABLISHED.
> 
> This change defeatures behavior that was previously allowed under the
> PSP uapi. My justification is:
> 
> Nothing useful can be done after association setup on closed or listen
> sockets today. Listen sockets could accept a PSP-encrypted TCP SYN, but
> the child socket will not inherit any PSP state. On the other side,
> establishing PSP state prior to connect() will result in a PSP-encrypted
> TCP SYN sent to a listening peer, which in turn has the aforementioned
> limitations. That implies that there cannot be any users of this
> feature, so it should be safe to remove it from the PSP uapi.
> 
> In theory, the check in the tx-assoc path is more restrictive than
> necessary. FIN_WAIT1/2, CLOSING, LAST_ACK and CLOSE_WAIT could be
> allowed, and the peer would accept PSP-encrypted ACKs in the
> post-FIN-sent states, or data in the half-close case, but it is simpler
> to disallow those states because they don't fit the upgrade model.

And preferable to do so. While it could be allowed, there is no real
use case for it. Simpler state model allows simpler code.

> The check in the tx-assoc path fixes a bug in commit 6b46ca260e22 ("net:
> psp: add socket security association code") where an unsynchronized
> write can be performed on an assoc shared with a timewait socket when
> the socket is in TCP_CLOSE after shutdown. This commit is not targeted
> at net because its premise of preventing listen sockets from holding
> assoc state depends on net-next commit 8cc3aef0cb19 ("tcp: Do not allow
> buggy transitions between ehash and lhash2.")
> 
> Signed-off-by: Daniel Zahka <daniel.zahka@gmail.com>

Reviewed-by: Willem de Bruijn <willemb@google.com>

Even if targeting to net-next, you could consider keeping the Fixes tag.
Importantly the prerequisite patch is mentioned. But is only one of two
mentioned here?