Date: Sun, 21 Jun 2020 20:31:22 +0200 From: Michael Tuexen <tuexen@freebsd.org> To: Ian Lepore <ian@freebsd.org> Cc: "bergerkos@yahoo.co.uk" <bergerkos@yahoo.co.uk>, "freebsd-current@freebsd.org" <freebsd-current@freebsd.org> Subject: =?utf-8?B?UmU6INCSINC+0YLQstC10YIg0L3QsDogdm5jIGNhbid0IGNvbm5l?= =?utf-8?B?Y3QgdG8gc29ja2V0?= Message-ID: <A004D004-2DC2-493D-9BBD-EEFD50359B60@freebsd.org> In-Reply-To: <8899ab009f5a2d6fca0cebd53913ca03a48f4861.camel@freebsd.org> References: <1559644055.2429905.1592721641280.ref@mail.yahoo.com> <1559644055.2429905.1592721641280@mail.yahoo.com> <1749874720.2583691.1592742539717@mail.yahoo.com> <5035A0D1-BF25-4483-BD52-75944EBBEF8E@freebsd.org> <ae6c2e2856e1e7193026c01821571d7f17e3d0f5.camel@freebsd.org> <E9CA2FDE-0F7E-47C8-BB3B-F00F2E471DF3@freebsd.org> <8899ab009f5a2d6fca0cebd53913ca03a48f4861.camel@freebsd.org>
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> On 21. Jun 2020, at 20:02, Ian Lepore <ian@freebsd.org> wrote: > > On Sun, 2020-06-21 at 19:54 +0200, Michael Tuexen wrote: >>> On 21. Jun 2020, at 19:40, Ian Lepore <ian@freebsd.org> wrote: >>> >>> On Sun, 2020-06-21 at 14:54 +0200, Michael Tuexen wrote: >>>>> On 21. Jun 2020, at 14:28, Kostya Berger <bergerkos@yahoo.co.uk >>>>>> >>>>> wrote: >>>>> >>>>> Ok, it turns out, it gives the previously mentioned error only >>>>> if I >>>>> use VNC server string 0.0.0.0:5900 (as I always did). in my VNC >>>>> client.But when replaced with127.0.0.1:5900it connects all >>>>> right. >>>> >>>> I don't hink 0.0.0.0 is a valid destination address you can use >>>> in >>>> connect(). Using 127.0.0.1 should >>>> be fine. >>>> >>>> I guess, https://svnweb.freebsd.org/changeset/base/361752 is the >>>> relevant commit here. >>>> >>> >>> *BSD has always accepted 0 as a synonym for localhost (and iirc, linux >>> does not). If this no longer works, it's a regression which is going >>> to cause existing applications and scripts to fail. At the very least >>> it deserves an entry in UPDATING. >> >> Hmm. 0.0.0.0 is a wildcard address, meaning any of my local addresses. >> I do understand how that works for binding a TCP socket you will be >> listening on. It just means accept TCP connections on all addresses. >> The destination address of the incoming SYN segment will determine which >> one to use. However, which of the local addresses should be used >> when calling connect() with 0.0.0.0? How should this choice be made? >> >> Best regards >> Michael >> > > I don't know. I had thought the idea was sanctioned by a couple RFCs, > but I just had a fresh look at them (1122, 5735) and it now appears to > me that in both cases it sanctions using 0.0.0.0 as a source address, > but not as a destination. So now I'm thinking maybe it has been a You can use 0.0.0.0 as a source address in specific packets (mainly ones where you don't know your local address like during address configuration), but you can't use it as a destination address. In the TCP case (which is we are looking at), you can't use it as a source or destination address. However, this issue is not about addresses in packets, but address usage in the API, the connect() call for TCP in particular. > historical mistake amongst the BSDs to accept it as a destination > address synonym for 127.0.0.1. That might be possible. But it would be much better to use 127.0.0.1 if you mean it. > > I was mostly just pointing out this change to no longer accept it is > going to be a big surprise to many people when it hits the streets in a > release. I know it's going to break things at $work, we'll have to > start combing around for uses of it and make changes. (Fixing my 20+ > years of finger-memory for "nc 0 <someport>" will be harder.) OK. I'll bring that up in the bi-weekly transport telco. It was clear to disallow multicast, but the patch also wanted to deal with 0.0.0.0. For IPv6, there is such a mapping from connect(::0) to connect(::1). So for consistency it might make sense to do/keep the same for IPv4. I need to look at the code why this is working at all for IPv4 as you say it is. Best regards Michael > > -- Ian > >
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