netdev - Re: [PATCHv2 net-next 3/5] sctp: add SCTP_EXPOSE_POTENTIALLY_FAILED

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Date:   Thu, 10 Oct 2019 08:40:45 -0400
From:   Neil Horman <nhorman@...driver.com>
To:     Xin Long <lucien.xin@...il.com>
Cc:     David Laight <David.Laight@...lab.com>,
        network dev <netdev@...r.kernel.org>,
        "linux-sctp@...r.kernel.org" <linux-sctp@...r.kernel.org>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        "davem@...emloft.net" <davem@...emloft.net>
Subject: Re: [PATCHv2 net-next 3/5] sctp: add
 SCTP_EXPOSE_POTENTIALLY_FAILED_STATE sockopt

On Thu, Oct 10, 2019 at 05:28:34PM +0800, Xin Long wrote:
> On Thu, Oct 10, 2019 at 12:18 AM Neil Horman <nhorman@...driver.com> wrote:
> >
> > On Tue, Oct 08, 2019 at 11:28:32PM +0800, Xin Long wrote:
> > > On Tue, Oct 8, 2019 at 9:02 PM David Laight <David.Laight@...lab.com> wrote:
> > > >
> > > > From: Xin Long
> > > > > Sent: 08 October 2019 12:25
> > > > >
> > > > > This is a sockopt defined in section 7.3 of rfc7829: "Exposing
> > > > > the Potentially Failed Path State", by which users can change
> > > > > pf_expose per sock and asoc.
> > > >
> > > > If I read these patches correctly the default for this sockopt in 'enabled'.
> > > > Doesn't this mean that old application binaries will receive notifications
> > > > that they aren't expecting?
> > > >
> > > > I'd have thought that applications would be required to enable it.
> > > If we do that, sctp_getsockopt_peer_addr_info() in patch 2/5 breaks.
> > >
> > I don't think we can safely do either of these things.  Older
> > applications still need to behave as they did prior to the introduction
> > of this notification, and we shouldn't allow unexpected notifications to
> > be sent.
> >
> > What if you added a check in get_peer_addr_info to only return -EACCESS
> > if pf_expose is 0 and the application isn't subscribed to the PF event?
> We can't subscribe to PF event only, but all the SCTP_PEER_ADDR_CHANGE
> events.
> 
> Now I'm thinking both PF event and "return -EACCES" in get_peer_addr_info
> are new, we should give 'expose' a default value that would disable both.
> How do think if we set 'pf_expose = -1' by default. We send the pf event
> only if (asoc->pf_expose > 0) in sctp_assoc_control_transport().
> 
And if pf_expose = 0, we send the event, and return -EACCESS if we call
the socket option and find a PF assoc?  If so, yes, I think that makes
sense.

Neil

> >
> > Neil
> >
> > > >
> > > >         David
> > > >
> > > > -
> > > > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> > > > Registration No: 1397386 (Wales)
> > > >
> > >
>