Question about D-Bus and cygrunsrv

Question about D-Bus and cygrunsrv

[Mike Brady]

Hi there. I'm trying to set up Shairport Sync as a CYGWIN service, and I'm trying to use cygrunsrv.

Briefly, I can get everything to work properly except the D-Bus interface -- when shairport-sync is installed as a service, it can't "own" a well-known name on the "system" D-Bus.

I built a configuration and installer for shairport sync essentially by copying the avahi-daemon-config file.

The Avahi deamon uses the system D-Bus successfully under the username "SYSTEM" and without (AFAICS) changing IDs. But for the life of me, I can't get Shairport Sync to work the same way.

Incidentally, if I change the D Bus policy file for Shairport Sync to be allowed to own its well-known name on D Bus when running under the logged in account, everything is peachy.

Any suggestions gratefully received. Incidentally, I'm the main developer of Shairport Sync -- https://github.com/mikebrady/shairport-sync.

Best wishes
Mike Brady


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Re: Question about D-Bus and cygrunsrv

[Mike Brady]

Hello again. Further to the rather vague email below, here is a link to what I did to install Shairport Sync on a fresh Cygwin installation: 

https://github.com/mikebrady/shairport-sync/blob/development/CYGWIN.md <https://github.com/mikebrady/shairport-sync/blob/development/CYGWIN.md>

Regards
Mike


> On 20 Feb 2019, at 21:50, Mike Brady <mikebrady@eircom.net> wrote:
> 
> Hi there. I'm trying to set up Shairport Sync as a CYGWIN service, and I'm trying to use cygrunsrv.
> 
> Briefly, I can get everything to work properly except the D-Bus interface -- when shairport-sync is installed as a service, it can't "own" a well-known name on the "system" D-Bus.
> 
> I built a configuration and installer for shairport sync essentially by copying the avahi-daemon-config file.
> 
> The Avahi deamon uses the system D-Bus successfully under the username "SYSTEM" and without (AFAICS) changing IDs. But for the life of me, I can't get Shairport Sync to work the same way.
> 
> Incidentally, if I change the D Bus policy file for Shairport Sync to be allowed to own its well-known name on D Bus when running under the logged in account, everything is peachy.
> 
> Any suggestions gratefully received. Incidentally, I'm the main developer of Shairport Sync -- https://github.com/mikebrady/shairport-sync.
> 
> Best wishes
> Mike Brady
> 


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Re: Question about D-Bus and cygrunsrv

[Corinna Vinschen]

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Hey Mike,

On Feb 21 16:56, Mike Brady wrote:
> Hello again. Further to the rather vague email below, here is a link to what I did to install Shairport Sync on a fresh Cygwin installation: 
> 
> https://github.com/mikebrady/shairport-sync/blob/development/CYGWIN.md <https://github.com/mikebrady/shairport-sync/blob/development/CYGWIN.md>
> 
> Regards
> Mike
> 
> 
> > On 20 Feb 2019, at 21:50, Mike Brady <mikebrady@eircom.net> wrote:
> > 
> > Hi there. I'm trying to set up Shairport Sync as a CYGWIN service, and I'm trying to use cygrunsrv.
> > 
> > Briefly, I can get everything to work properly except the D-Bus interface -- when shairport-sync is installed as a service, it can't "own" a well-known name on the "system" D-Bus.
> > 
> > I built a configuration and installer for shairport sync essentially by copying the avahi-daemon-config file.
> > 
> > The Avahi deamon uses the system D-Bus successfully under the username "SYSTEM" and without (AFAICS) changing IDs. But for the life of me, I can't get Shairport Sync to work the same way.
> > 
> > Incidentally, if I change the D Bus policy file for Shairport Sync to be allowed to own its well-known name on D Bus when running under the logged in account, everything is peachy.
> > 
> > Any suggestions gratefully received. Incidentally, I'm the main developer of Shairport Sync -- https://github.com/mikebrady/shairport-sync.
> > 
> > Best wishes
> > Mike Brady
> > 

You have been heard, but I have not the faintest clue what d-bus or,
FWIW, avahi are doing.  Ideally, if you could break down the problem
to a simple, self-contained testcase which shows what exactly is not
working on a plain libc level, help may be possible :}


Corinna

-- 
Corinna Vinschen
Cygwin Maintainer

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Re: Question about D-Bus and cygrunsrv

[Mike Brady]

Thanks for the response, Corinna, and the suggestion. I will do that and come back to you guys.
Mike


> On 22 Feb 2019, at 09:55, Corinna Vinschen <corinna-cygwin@cygwin.com> wrote:
> 
> Hey Mike,
> 
> On Feb 21 16:56, Mike Brady wrote:
>> Hello again. Further to the rather vague email below, here is a link to what I did to install Shairport Sync on a fresh Cygwin installation: 
>> 
>> https://github.com/mikebrady/shairport-sync/blob/development/CYGWIN.md <https://github.com/mikebrady/shairport-sync/blob/development/CYGWIN.md> <https://github.com/mikebrady/shairport-sync/blob/development/CYGWIN.md <https://github.com/mikebrady/shairport-sync/blob/development/CYGWIN.md>>
>> 
>> Regards
>> Mike
>> 
>> 
>>> On 20 Feb 2019, at 21:50, Mike Brady <mikebrady@eircom.net> wrote:
>>> 
>>> Hi there. I'm trying to set up Shairport Sync as a CYGWIN service, and I'm trying to use cygrunsrv.
>>> 
>>> Briefly, I can get everything to work properly except the D-Bus interface -- when shairport-sync is installed as a service, it can't "own" a well-known name on the "system" D-Bus.
>>> 
>>> I built a configuration and installer for shairport sync essentially by copying the avahi-daemon-config file.
>>> 
>>> The Avahi deamon uses the system D-Bus successfully under the username "SYSTEM" and without (AFAICS) changing IDs. But for the life of me, I can't get Shairport Sync to work the same way.
>>> 
>>> Incidentally, if I change the D Bus policy file for Shairport Sync to be allowed to own its well-known name on D Bus when running under the logged in account, everything is peachy.
>>> 
>>> Any suggestions gratefully received. Incidentally, I'm the main developer of Shairport Sync -- https://github.com/mikebrady/shairport-sync.
>>> 
>>> Best wishes
>>> Mike Brady
>>> 
> 
> You have been heard, but I have not the faintest clue what d-bus or,
> FWIW, avahi are doing.  Ideally, if you could break down the problem
> to a simple, self-contained testcase which shows what exactly is not
> working on a plain libc level, help may be possible :}
> 
> 
> Corinna
> 
> -- 
> Corinna Vinschen
> Cygwin Maintainer


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Re: Question about D-Bus and cygrunsrv

[René Berber]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA256

On 2/22/2019 3:55 AM, Corinna Vinschen wrote:

>>> On 20 Feb 2019, at 21:50, Mike Brady <mikebrady@eircom.net> 
>>> wrote:
>>> 
>>> Hi there. I'm trying to set up Shairport Sync as a CYGWIN 
>>> service, and I'm trying to use cygrunsrv.
>>> 
>>> Briefly, I can get everything to work properly except the
>>> D-Bus interface -- when shairport-sync is installed as a
>>> service, it can't "own" a well-known name on the "system"
>>> D-Bus.
>>> 
>>> I built a configuration and installer for shairport sync 
>>> essentially by copying the avahi-daemon-config file.
>>> 
>>> The Avahi deamon uses the system D-Bus successfully under the 
>>> username "SYSTEM" and without (AFAICS) changing IDs. But for 
>>> the life of me, I can't get Shairport Sync to work the same 
>>> way.
>>> 
>>> Incidentally, if I change the D Bus policy file for Shairport 
>>> Sync to be allowed to own its well-known name on D Bus when 
>>> running under the logged in account, everything is peachy.
[snip]
> You have been heard, but I have not the faintest clue what d-bus 
> or, FWIW, avahi are doing.  Ideally, if you could break down the 
> problem to a simple, self-contained testcase which shows what 
> exactly is not working on a plain libc level, help may be possible 
> :}

My guess is that its a permission problem: D-Bus by default on Windows
uses unix sockets (fills up your temp directory with those pesky files :
- -)

In Cygwin the temp directory has the sticky permission (t), but the
socket file created by the server most likely doesn't have access for
anybody else.

Check those permissions to maybe get a clue.

The problem comes from upstream, I'm just not sure because I used to
build my own, patched, version of DBUS (for a workaround which is to
use tcp, not unix sockets... but the Windows maintainer says "nobody
uses tcp sockets on Windows", and then they "improved" security which
is why I suspect access permissions).
- -- 
R.Berber
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Re: Question about D-Bus and cygrunsrv

[L A Walsh]

On 2/22/2019 2:16 PM, René Berber wrote:
>
>
> My guess is that its a permission problem: D-Bus by default on Windows
> uses unix sockets (fills up your temp directory with those pesky files :
> - -)
>
> In Cygwin the temp directory has the sticky permission (t), but the
> socket file created by the server most likely doesn't have access for
> anybody else.
>   
---
    I'm not sure, but I'd think dbus demon would be enabled to
talk to the system socket
> Check those permissions to maybe get a clue.
>
> The problem comes from upstream, I'm just not sure because I used to
> build my own, patched, version of DBUS (for a workaround which is to
> use tcp, not unix sockets... but the Windows maintainer says "nobody
> uses tcp sockets on Windows", and then they "improved" security which
> is why I suspect access permissions).
>   
---
    Yeah, they are more than a little bit security paranoid.

I'd like to get the dbus sessions between my desktop & server to talk --
like when I am running an X-app, and press help, it really would be
better if it brought up the browser on my desktop instead of one
on the server via X.

I had hopes as one of their examples specifies tcp in the protocol
field, but supposedly the tcp doesn't work and likely won't due to
security concerns -- mainly because the bus architecture was structured
around the idea of an internal HW bus -- where normally there isn't
much in the way of security.  If they allowed it to be open to
a network, then they think everyone on the internet will have access
and that dbus will be blaimed for a security problem.

I did mention that some people use closed nets between machines
and should be allowed to use dbus to talk between them where desirable,
but he thinks that most hand-held users wouldn't know how to isolate
a net.  On top of that, dbus doesn't have the ability to categorize
if the net is public, private(home) or enterprise(work).  Seemed
like a pain to get working for what would be a plus for me, but
not sure about demand, not to mention working with such paranoid
folk really can be frustrating.

There's a dbus list where they talk about development and security
issues @

https://lists.freedesktop.org/mailman/listinfo/dbus

best of luck!





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Re: Question about D-Bus and cygrunsrv

[Mike Brady]

Thanks for the comments. I’ll certainly check the security side of things.

What is a bit intriguing is that another application — the Avahi daemon (see http://avahi.org) that provides ZeroConf / Bonjour service discovery services — also uses the D-Bus system bus and it works fine as a cygrunsrv-based daemon. The difference between the two applications with respect to D-Bus is that Shairport Sync uses the high-level GDbus interface that is part of GIO (https://developer.gnome.org/gio/stable/ch01.html), whereas the Avahi daemon uses the dbus library directly.

Mike

> On 26 Feb 2019, at 06:51, L A Walsh <cygwin@tlinx.org> wrote:
> 
> On 2/22/2019 2:16 PM, René Berber wrote:
>> 
>> 
>> My guess is that its a permission problem: D-Bus by default on Windows
>> uses unix sockets (fills up your temp directory with those pesky files :
>> - -)
>> 
>> In Cygwin the temp directory has the sticky permission (t), but the
>> socket file created by the server most likely doesn't have access for
>> anybody else.
>> 
> ---
>    I'm not sure, but I'd think dbus demon would be enabled to
> talk to the system socket
>> Check those permissions to maybe get a clue.
>> 
>> The problem comes from upstream, I'm just not sure because I used to
>> build my own, patched, version of DBUS (for a workaround which is to
>> use tcp, not unix sockets... but the Windows maintainer says "nobody
>> uses tcp sockets on Windows", and then they "improved" security which
>> is why I suspect access permissions).
>> 
> ---
>    Yeah, they are more than a little bit security paranoid.
> 
> I'd like to get the dbus sessions between my desktop & server to talk --
> like when I am running an X-app, and press help, it really would be
> better if it brought up the browser on my desktop instead of one
> on the server via X.
> 
> I had hopes as one of their examples specifies tcp in the protocol
> field, but supposedly the tcp doesn't work and likely won't due to
> security concerns -- mainly because the bus architecture was structured
> around the idea of an internal HW bus -- where normally there isn't
> much in the way of security.  If they allowed it to be open to
> a network, then they think everyone on the internet will have access
> and that dbus will be blaimed for a security problem.
> 
> I did mention that some people use closed nets between machines
> and should be allowed to use dbus to talk between them where desirable,
> but he thinks that most hand-held users wouldn't know how to isolate
> a net.  On top of that, dbus doesn't have the ability to categorize
> if the net is public, private(home) or enterprise(work).  Seemed
> like a pain to get working for what would be a plus for me, but
> not sure about demand, not to mention working with such paranoid
> folk really can be frustrating.
> 
> There's a dbus list where they talk about development and security
> issues @
> 
> https://lists.freedesktop.org/mailman/listinfo/dbus
> 
> best of luck!
> 
> 
> 
> 


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Re: Question about D-Bus and cygrunsrv

[Mike Brady]

Hello again.

I've returned to this continuing problem and come up with a short piece of code which seems to exemplify this problem. It works in Linux and doesn't work in Cygwin.

Basically, the code is an attempt to get a "name" on the D-Bus "system bus" which could be used to provide a system-wide service using the D-Bus IPC protocol.

The attempt to get a name succeeds on Linux (Ubuntu 19.04) and fails on Cygwin (3.0.7). The code uses the high-level GDbus interface that is part of GIO (https://developer.gnome.org/gio/stable/ch01.html <https://developer.gnome.org/gio/stable/ch01.html>).

Another piece of sample code that uses the regular D-Bus library (libdbus1-devel in Cygwin) seems to work perfectly, which seems to me to suggest that whatever this probelm is, it is not a security issue.

Both of these samples are set up as automake projects and include config and policy files. I'd be happy to share or publish them wherever convenient...

Regards
Mike


> On 22 Feb 2019, at 09:55, Corinna Vinschen <corinna-cygwin@cygwin.com> wrote:
> 
> Hey Mike,
> 
> On Feb 21 16:56, Mike Brady wrote:
>> Hello again. Further to the rather vague email below, here is a link to what I did to install Shairport Sync on a fresh Cygwin installation: 
>> 
>> https://github.com/mikebrady/shairport-sync/blob/development/CYGWIN.md <https://github.com/mikebrady/shairport-sync/blob/development/CYGWIN.md> <https://github.com/mikebrady/shairport-sync/blob/development/CYGWIN.md <https://github.com/mikebrady/shairport-sync/blob/development/CYGWIN.md>>
>> 
>> Regards
>> Mike
>> 
>> 
>>> On 20 Feb 2019, at 21:50, Mike Brady <mikebrady@eircom.net> wrote:
>>> 
>>> Hi there. I'm trying to set up Shairport Sync as a CYGWIN service, and I'm trying to use cygrunsrv.
>>> 
>>> Briefly, I can get everything to work properly except the D-Bus interface -- when shairport-sync is installed as a service, it can't "own" a well-known name on the "system" D-Bus.
>>> 
>>> I built a configuration and installer for shairport sync essentially by copying the avahi-daemon-config file.
>>> 
>>> The Avahi deamon uses the system D-Bus successfully under the username "SYSTEM" and without (AFAICS) changing IDs. But for the life of me, I can't get Shairport Sync to work the same way.
>>> 
>>> Incidentally, if I change the D Bus policy file for Shairport Sync to be allowed to own its well-known name on D Bus when running under the logged in account, everything is peachy.
>>> 
>>> Any suggestions gratefully received. Incidentally, I'm the main developer of Shairport Sync -- https://github.com/mikebrady/shairport-sync.
>>> 
>>> Best wishes
>>> Mike Brady
>>> 
> 
> You have been heard, but I have not the faintest clue what d-bus or,
> FWIW, avahi are doing.  Ideally, if you could break down the problem
> to a simple, self-contained testcase which shows what exactly is not
> working on a plain libc level, help may be possible :}
> 
> 
> Corinna
> 
> -- 
> Corinna Vinschen
> Cygwin Maintainer


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Re: Question about D-Bus and cygrunsrv

[Mike Brady]

Just as a quick follow-up, I've put the two code samples up on github:

https://github.com/mikebrady/dbus-example <https://github.com/mikebrady/dbus-example> -- this uses the regular dbus1 library and works on Linux and Cygwin.
https://github.com/mikebrady/gdbus-example <https://github.com/mikebrady/gdbus-example> -- this uses the GDbus library from GIO and works in Linux but not in Cygwin.


Best wishes
Mike


> On 22 Oct 2019, at 15:07, Mike Brady <mikebrady@eircom.net> wrote:
> 
> Hello again.
> 
> I've returned to this continuing problem and come up with a short piece of code which seems to exemplify this problem. It works in Linux and doesn't work in Cygwin.
> 
> Basically, the code is an attempt to get a "name" on the D-Bus "system bus" which could be used to provide a system-wide service using the D-Bus IPC protocol.
> 
> The attempt to get a name succeeds on Linux (Ubuntu 19.04) and fails on Cygwin (3.0.7). The code uses the high-level GDbus interface that is part of GIO (https://developer.gnome.org/gio/stable/ch01.html <https://developer.gnome.org/gio/stable/ch01.html>).
> 
> Another piece of sample code that uses the regular D-Bus library (libdbus1-devel in Cygwin) seems to work perfectly, which seems to me to suggest that whatever this probelm is, it is not a security issue.
> 
> Both of these samples are set up as automake projects and include config and policy files. I'd be happy to share or publish them wherever convenient...
> 
> Regards
> Mike
> 
> 
>> On 22 Feb 2019, at 09:55, Corinna Vinschen <corinna-cygwin@cygwin.com <mailto:corinna-cygwin@cygwin.com>> wrote:
>> 
>> Hey Mike,
>> 
>> On Feb 21 16:56, Mike Brady wrote:
>>> Hello again. Further to the rather vague email below, here is a link to what I did to install Shairport Sync on a fresh Cygwin installation: 
>>> 
>>> https://github.com/mikebrady/shairport-sync/blob/development/CYGWIN.md <https://github.com/mikebrady/shairport-sync/blob/development/CYGWIN.md> <https://github.com/mikebrady/shairport-sync/blob/development/CYGWIN.md <https://github.com/mikebrady/shairport-sync/blob/development/CYGWIN.md>>
>>> 
>>> Regards
>>> Mike
>>> 
>>> 
>>>> On 20 Feb 2019, at 21:50, Mike Brady <mikebrady@eircom.net <mailto:mikebrady@eircom.net>> wrote:
>>>> 
>>>> Hi there. I'm trying to set up Shairport Sync as a CYGWIN service, and I'm trying to use cygrunsrv.
>>>> 
>>>> Briefly, I can get everything to work properly except the D-Bus interface -- when shairport-sync is installed as a service, it can't "own" a well-known name on the "system" D-Bus.
>>>> 
>>>> I built a configuration and installer for shairport sync essentially by copying the avahi-daemon-config file.
>>>> 
>>>> The Avahi deamon uses the system D-Bus successfully under the username "SYSTEM" and without (AFAICS) changing IDs. But for the life of me, I can't get Shairport Sync to work the same way.
>>>> 
>>>> Incidentally, if I change the D Bus policy file for Shairport Sync to be allowed to own its well-known name on D Bus when running under the logged in account, everything is peachy.
>>>> 
>>>> Any suggestions gratefully received. Incidentally, I'm the main developer of Shairport Sync -- https://github.com/mikebrady/shairport-sync <https://github.com/mikebrady/shairport-sync>.
>>>> 
>>>> Best wishes
>>>> Mike Brady
>>>> 
>> 
>> You have been heard, but I have not the faintest clue what d-bus or,
>> FWIW, avahi are doing.  Ideally, if you could break down the problem
>> to a simple, self-contained testcase which shows what exactly is not
>> working on a plain libc level, help may be possible :}
>> 
>> 
>> Corinna
>> 
>> -- 
>> Corinna Vinschen
>> Cygwin Maintainer
> 


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