path: root/open_issues/dbus.mdwn

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[[!tag open_issue_hurd]]

The dbus problems are due to missing scm credentials [[sendmsg_scm_creds]] and socket credentials
[[pflocal_socket_credentials_for_local_sockets]]. There was also a problem with short timeout in 
[[select]], but that has been solved in Debian by setting a minimum timeout of 1ms.

[[!toc]]


# IRC, freenode, #hurd, 2011-11-26

    <antrik> BTW, how much effort is necessary to fix dbus?
    <pinotree> basically, have pflocal know who's the sender
      (pid/uid/gid/groups) in the socket send op


# IRC, freenode, #hurd, 2011-12-16

    <braunr> pinotree: what's the problem with dbus ?
    <pinotree> braunr: select() returning 0 changed fd's with very short (eg <
      1ms) timeouts when there are actually events;

[[select]].

    <pinotree> and missing socket credentials

[[sendmsg_scm_creds]].

    <braunr> oh
    <braunr> which socket creds interface ?
    <pinotree> bsd, i.e. with SCM_CREDENTIALS payload for cmsg on
      {recv,send}msg()
    <braunr> ok
    <braunr> SCM_RIGHTS too ?
    <braunr> the select issue seems weird though
    <pinotree> hm no, that's for passing fd's to other processes
    <braunr> is it specific to pflocal or does dbus use pfinet too ?
    <pinotree> iirc on very short timeouts the application has no time waiting
      for the reply of servers
    <braunr> i see
    <pinotree> braunr: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=79358
    <braunr> thanks
    <pinotree> (the interesting messages are from #53 and on)
    <braunr> 2000 eh ... :)
    <braunr> hm i agree with neal, i don't understand why the timeout is given
      to the kernel as part of the mach_msg call


# IRC, freenode, #hurd, 2011-12-20

    <braunr> hm, i don't see any occurrence of SCM_CREDENTIALS in dbus
    <braunr> only SCM_RIGHTS
    <pinotree> braunr: yes, that one
    <braunr> oh
    <braunr> i thought you said the opposite last time
    <pinotree> dbus/dbus-sysdeps-unix.c, write_credentials_byte and
      _dbus_read_credentials_socket (with #define HAVE_CMSGCRED)
    <braunr> hm
    <braunr> which version ?
    <braunr> i don't see anything in 1.4.16
    <pinotree> 1.4.16
    <braunr> grmbl
    <braunr> ah, i see
    <braunr> SCM_CREDS
    <pinotree> if you want, i have a simplier .c source with it
    <braunr> no i'm just gathering info
    <pinotree> ok
    <braunr> what's the deal with SCM_CREDS and SCM_CREDENTIALS ?
    <braunr> bsd vs sysv ?
    <braunr> oh, http://lists.debian.org/debian-hurd/2002/03/msg00135.html
    <braunr> so we actually do want both SCM_CREDS and SCM_RIGHTS for debus
    <braunr> dbus
    <pinotree> SCM_RIGHTS is a different matter, it is for passing fd's
    <braunr> yes
    <braunr> but it's used by dbus
    <braunr> so if we can get it, it should help too
    <pinotree> there's a preliminary patch for it done by emilio time ago, and
      iirc it's applied to debian's glibc
    <braunr> ah, he changed the libc
    <braunr> right, that's the only sane way
    <pinotree> iirc roland didn't like one or more parts of it (but i could be
      wrong)
    <braunr> ok


# IRC, freenode, #hurd, 2013-07-17

    <teythoon> btw pinotree, what happened to your efforts to make dbus work?
    <pinotree> not much, my initial patch was just a crude hack, a better
      solution requires more thinkering and work 
    <teythoon> yes, ive seen that
    <teythoon> but that was only a tiny patch against the libc, surely there
      must be more to that?
    <pinotree> not really
    <teythoon> and the proper fix is to patch pflocal to query the auth server
      and add the credentials?
    <pinotree> possibly
    <teythoon> that doesn't sound to bad, did you give it a try?
    <pinotree> not really, got caught in other stuff


# IRC, freenode, #hurd, 2013-09-02

    <gnu_srs1> something is wrong with libc0.3 since the switch to 2.17. dbus
      does not run any longer when rebuilt
    <gnu_srs1> the latest build of dbus was with 2.13: libc0.3-dev: already
      installed (2.13-38)
    <pinotree> debug it
    <gnu_srs1> Yes, I will. Maybe somebody could rebuild it and verify my
      findings?
    <pinotree> gnu_srs1: your finding is "doesn't work", which is generic and
      does not help without investigation
    <gnu_srs1> just rebuild it and: e.g. ./build-debug/bus/dbus-daemon --system
      (--nofork)
    <pinotree> gnu_srs1: please, debug it
    <gnu_srs1> I have partially already. But maybe the problems only shows on
      my box. I'll rebuild on another box before continuing debugging.
    <pinotree> gnu_srs1: are you, by chance, running a libc or something else
      with your scm_creds work?
    <gnu_srs1> I did, but I've backed to 2.17-92 right now.
    <gnu_srs1> sane problem with dbus on another box, something's fishy:-(
    <gnu_srs1> braunr: any good way to find out if the dbus problems are with
      libpthread? Setting a breakpoint with libc0.3-dbg installed.
    <braunr> gnu_srs1: i don't know

See [[glibc]], *Missing interfaces, amongst many more*, *`SOCK_CLOEXEC`*.


# IRC, freenode, #hurd, 2013-09-04

    <gnu_srs> Hi, looks like dbus requires abstract socket namespace: #undef
      HAVE_ABSTRACT_SOCKETS What's missing?
    <pinotree> uh?
    <pinotree> abstract unix sockets are a Linux feature, and surely it is not
      mandatory for dbus
    <gnu_srs> Looks like dbus exits if they are not supported:
    <gnu_srs>  dbus_set_error (error, DBUS_ERROR_NOT_SUPPORTED,  "Operating
      system does not support abstract socket namespace\n");        _dbus_close
      (listen_fd, NULL);  1061       return -1;
    <pinotree> that is enclosed in a if (abstract)
    <pinotree> and that parameter is set to true in other places (eg
      dbus/dbus-server-unix.c) only when HAVE_ABSTRACT_SOCKETS is defined
    <pinotree> so no, abstract sockets are not mandatory
    <gnu_srs> Well this code is executed e.g. when running emacs remotely in
      X. Have to dig deeper then to see why.
    <pinotree> maybe it could have to do the fact that your dbus server is
      running in linux and runs by default using such sockets type
    <pinotree> but yes, you need to dig better
    <gnu_srs> pinotree: You are right. when running natively the problem is:
    <pinotree> *drums*
    <gnu_srs> Manually: Process /usr/lib/at-spi2-core/at-spi-bus-launcher
      exited with status 1
    <pinotree> eh?
    <gnu_srs> Error retrieving accessibility bus address:
      org.freedesktop.DBus.Error.Spawn.ChildExited: ^
    <pinotree> most probably that service does not start due to the lack of
      socket credentials which affects dbus
    <pinotree> uninstall or disable those additional services, they are not
      your problem
    <gnu_srs> credentials is enabled. which services to remove?
    <pinotree> dunno


# IRC, freenode, #hurd, 2013-09-11

    <gnu_srs> Hi, looks like frebsd had (2008) the same problem as hurd when
      sending credentials over PF_INET: 
    <gnu_srs>
      http://lists.freebsd.org/pipermail/freebsd-hackers/2008-May/024577.html
    <gnu_srs> Since the dbus code is about the same now (2013), maybe they
      added support?
    <gnu_srs> The next message in the thread confirms that the dbus code is
      invalid, does anybody have pointers?
    <pinotree> from what i've seen so far, socket credentials are done only for
      local sockets (ie PF_UNIX)
    <pinotree> i don't see how things like uid/gid/pid of the socket endpoint
      can have anything to do with AF_INET
    <pinotree> and socket credentials in dbus are used only in the [local]
      socket transport, so there's no issue


# IRC, freenode, #hurd, 2013-09-12

    <gnu_srs> pinotree: Yes, there is an issue with dbus and AF_INET, see
      test/corrupt.c: tests /corrupt/tcp and /corrupt/byte-order/tcp:-/
    <pinotree> gnu_srs: what's wrong with those? they are just testing the
      connection over a tcp socket
    <pinotree> as said above, socket credentials shouldn't be used in such
      cases
    <gnu_srs> They are, see also test/relay.c: /relay and /limit tests:-(
    <pinotree> how are they?
    <pinotree> please be more specifc...
    <gnu_srs> Just run the tests yourself with DBUS_VERBOSE=1
    <pinotree> you are claiming there is a problem, so please specify what is
      the actual issue
    <gnu_srs>  DBUS_VERBOSE=1 build-debug/test/test-relay 
    <pinotree> you are claiming there is a problem, so please specify what is
      the actual issue
    <gnu_srs> same with test-corrupt
    <gnu_srs> look at the verbose output:  Failed to write credentials: Failed
      to write credentials byte: Invalid argument
    <gnu_srs> coming from pfinet since PF_INET is used.
    <pinotree> check what it does on linux then
    <pinotree> put an abort() at the start of the read/write socket credential
      functions in dbus-sysdeps-unix.c and see whether it is triggered also on
      linux
    <gnu_srs> SO_PEERCRED is used for linux and LOCAL_CREDS is used for
      kfreebsd, so we are on our own here:-/
    <pinotree> and linux' SO_PEERCRED works also on AF_INET sockets? i'd doubt
      it
    <gnu_srs>
      http://stackoverflow.com/questions/10037086/so-peercred-vs-scm-credentials-why-there-are-both-of-them
    <pinotree> yes, i know the difference, but please read what i asked again
    <gnu_srs> I'll check to be sure...
    <braunr> gnu_srs: user credentials are not supposed to be passed through an
      AF_INET socket
    <braunr> how hard is that to understand ?
    <gnu_srs> OK, linux use send since CMSGCREDS is not defined to write
      credentials. Working on how they are received.
    <gnu_srs> braunr: I do understand, but the dbus code tries to do that for
      Hurd:-(
    <pinotree> then it should do that on linux too
    <pinotree> (since the local socket credentials code is isolated in own
      functions, and they are called only for the unix transport)
    <gnu_srs> Happiness:-D, almost all dbus tests pass!
    <gnu_srs> 17(17) dbus tests pass:)
    <braunr> gnu_srs: hopefully your patch does things right
    <gnu_srs> which patch
    <braunr> adding credentials through unix socket
    <braunr> isn't that what you're doing ?
    <gnu_srs> the mail to MLs is from the stock installed packages.
    <braunr> ?
    <gnu_srs> the test reports are with the SCM_CREDS patches, but I stumbled
      on the SCM_RIGHTS issues reported to MLs
    <gnu_srs> no patches applied, just test the attached file yourself.
    <braunr> so what's your work about ?
    <gnu_srs> I'm working on SCM_CREDS, yes, and created patches for dbus,
      glib2.0 and libc.
    <gnu_srs> the mail was about some bug in the call to io_restrict_auth in
      sendmsg.c: without any of my patches applied (another image) 
    <teythoon> gnu_srs: you have to give us more context, how are we supposed
      to know how to find this sendmsg.c file?
    <pinotree> (it's in glibc, but otherwise the remark is valid)
    <pinotree> s/otherwise/anyway/