netdev - Re: [PATCH net-next 0/7] rtnetlink: add RTM

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Message-ID: <15579097-D689-4CBC-AE9E-B554527C71DF@brauner.io>
Date:   Thu, 27 Sep 2018 22:31:37 +0200
From:   Christian Brauner <christian@...uner.io>
To:     David Ahern <dsahern@...il.com>, jbenc@...hat.com,
        davem@...emloft.net, stephen@...workplumber.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 0/7] rtnetlink: add RTM_GETADDR2

On September 27, 2018 10:24:36 PM GMT+02:00, David Ahern <dsahern@...il.com> wrote:
>On 9/27/18 11:58 AM, Christian Brauner wrote:
>> Various userspace programs (e.g. iproute2) have sent RTM_GETADDR
>> requests with struct ifinfomsg. This is wrong and should have been
>> struct ifaddrmsg all along as mandated by the manpages. However, dump
>> requests so far didn't parse the netlink message that was sent and
>> succeeded even when a wrong struct was passed along.
>
>...
>
>> The correct solution at this point seems to me to introduce a new
>> RTM_GETADDR2 request. This way we can parse the message and fail hard
>if
>> the struct is not struct ifaddrmsg and can safely extend it in the
>> future. Userspace tools that rely on the buggy RTM_GETADDR API will
>> still keep working without even having to see any log messages and
>new
>> userspace tools that want to make user of new features can make use
>of
>> the new RTM_GETADDR2 requests.
>
>First, I think this is the wrong precedent when all we need is a single
>bit flag that userspace can use to tell the kernel "I have a clue and I
>am passing in the proper header for this dump request".

That had been NAKed previously but if you have an idea that will be accepted all the more power to you.

>
>Second, you are not addressing the problems of the past by requiring
>the
>proper header and checking values passed in it.

I don't follow. RTM_GETADDR requests are absolutely unchanged. The full legacy behavior is restored by this patchset.

And requiring that RTM_GETADDR2 requests always pass the correct header is absolutely fine. We don't want built invalid legacy behavior into a new request  type.

>
>I have another idea. I'll send an RFC patch soon.