netdev - Re: [PATCH v10 2/4] net/handshake: Create a NETLINK service for handling handshake requests

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Date:   Thu, 20 Apr 2023 17:57:44 +0000
From:   Chuck Lever III <chuck.lever@...cle.com>
To:     Nathan Chancellor <nathan@...nel.org>
CC:     Chuck Lever <cel@...nel.org>, Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "kernel-tls-handshake@...ts.linux.dev" 
        <kernel-tls-handshake@...ts.linux.dev>
Subject: Re: [PATCH v10 2/4] net/handshake: Create a NETLINK service for
 handling handshake requests



> On Apr 20, 2023, at 1:56 PM, Nathan Chancellor <nathan@...nel.org> wrote:
> 
> Hi Chuck,
> 
> On Mon, Apr 17, 2023 at 10:32:26AM -0400, Chuck Lever wrote:
>> From: Chuck Lever <chuck.lever@...cle.com>
>> 
>> When a kernel consumer needs a transport layer security session, it
>> first needs a handshake to negotiate and establish a session. This
>> negotiation can be done in user space via one of the several
>> existing library implementations, or it can be done in the kernel.
>> 
>> No in-kernel handshake implementations yet exist. In their absence,
>> we add a netlink service that can:
>> 
>> a. Notify a user space daemon that a handshake is needed.
>> 
>> b. Once notified, the daemon calls the kernel back via this
>>   netlink service to get the handshake parameters, including an
>>   open socket on which to establish the session.
>> 
>> c. Once the handshake is complete, the daemon reports the
>>   session status and other information via a second netlink
>>   operation. This operation marks that it is safe for the
>>   kernel to use the open socket and the security session
>>   established there.
>> 
>> The notification service uses a multicast group. Each handshake
>> mechanism (eg, tlshd) adopts its own group number so that the
>> handshake services are completely independent of one another. The
>> kernel can then tell via netlink_has_listeners() whether a handshake
>> service is active and prepared to handle a handshake request.
>> 
>> A new netlink operation, ACCEPT, acts like accept(2) in that it
>> instantiates a file descriptor in the user space daemon's fd table.
>> If this operation is successful, the reply carries the fd number,
>> which can be treated as an open and ready file descriptor.
>> 
>> While user space is performing the handshake, the kernel keeps its
>> muddy paws off the open socket. A second new netlink operation,
>> DONE, indicates that the user space daemon is finished with the
>> socket and it is safe for the kernel to use again. The operation
>> also indicates whether a session was established successfully.
>> 
>> Signed-off-by: Chuck Lever <chuck.lever@...cle.com>
> ...
>> net/handshake/netlink.c                    |  312 ++++++++++++++++++++++++++
> ...
>> +static struct pernet_operations __net_initdata handshake_genl_net_ops = {
>> + .init = handshake_net_init,
>> + .exit = handshake_net_exit,
>> + .id = &handshake_net_id,
>> + .size = sizeof(struct handshake_net),
>> +};
> ...
>> +static void __exit handshake_exit(void)
>> +{
>> + unregister_pernet_subsys(&handshake_genl_net_ops);
>> + handshake_net_id = 0;
>> +
>> + handshake_req_hash_destroy();
>> + genl_unregister_family(&handshake_nl_family);
>> +}
>> +
>> +module_init(handshake_init);
>> +module_exit(handshake_exit);
> 
> I am not sure if this has been reported yet but it appears this
> introduces a section mismatch warning in several configurations
> according to KernelCI:
> 
> https://lore.kernel.org/6441748e.170a0220.531bd.8013@mx.google.com/
> 
>  $ make -skj"$(nproc)" ARCH=mips CROSS_COMPILE=mips-linux- O=build jazz_defconfig all
>  ...
>  WARNING: modpost: vmlinux.o: section mismatch in reference: handshake_exit (section: .exit.text) -> handshake_genl_net_ops (section: .init.data)
> 
> I guess '__net_initdata' should be dropped from handshake_genl_net_ops?

Thanks, Geert just sent a patch to fix that.


--
Chuck Lever