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List:       kde-frameworks-devel
Subject:    Re: Review Request 128790: Remove usage of utempter
From:       Oswald Buddenhagen <ossi () kde ! org>
Date:       2016-08-28 14:33:02
Message-ID: 20160828143302.27514.49837 () mimi ! kde ! org
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> On Aug. 28, 2016, 1:41 p.m., Oswald Buddenhagen wrote:
> > uhm, and why do you think utempter is the preferred choice?
> > last time i checked, nobody was shipping konsole setgid utmp. with kdeinit, \
> > that's not even an option. 
> > there are several options how to deal with this:
> > - fork()/wait() around the utempter calls, so it can't mess with the signal \
> > handling of the current process. though i seem to remmber that the addToUtmp() \
> >                 call actually uses the PID
> > - re-implement the libutempter calls with QProcess. that's actually how it was \
> > originally, but was changed because there were incompatible versions of utempter \
> >                 - but that seems like a minor concern compared to the status quo.
> > - drop utmp handling altogether, as it's been mostly superseded, first by \
> > consolekit, and now logind. however, respective bindings would have to be \
> > actually implemented, and i have no clue how things are supposed to be done. just \
> >                 some dbus calls?
> > -- what about non-linux systems?
> 
> Martin Tobias Holmedahl Sandsmark wrote:
> > uhm, and why do you think utempter is the preferred choice?
> > last time i checked, nobody was shipping konsole setgid utmp. with kdeinit, \
> > that's not even an option.
> 
> Why is the fallback code there at all, then?
> 
> 
> > - fork()/wait() around the utempter calls, so it can't mess with the signal \
> > handling of the current process. though i seem to remmber that the addToUtmp() \
> > call actually uses the PID
> 
> Won't that break if another process exits at the wrong time?
> 
> 
> > - re-implement the libutempter calls with QProcess. that's actually how it was \
> > originally, but was changed because there were incompatible versions of utempter \
> > - but that seems like a minor concern compared to the status quo.
> 
> I looked at that as well, the issue is finding the correct path for the utempter \
> helper. 
> 
> > - drop utmp handling altogether, as it's been mostly superseded, first by \
> > consolekit, and now logind. however, respective bindings would have to be \
> > actually implemented, and i have no clue how things are supposed to be done. just \
> > some dbus calls?
> 
> There seems to be a simple dbus call to register with logind at least. I tried \
> looking briefly at it, but I couldn't quickly find any logind code that did utmp \
> stuff. I didn't look very hard, though. 
> 
> > -- what about non-linux systems?
> 
> libutempter only supports Linux and FreeBSD, the fallback code seems to at least \
> try to be compatible with other platforms.

> Why is the fallback code there at all, then?

it was there first. it will actually work if somebody runs konsole as root. which \
nobody does, of course.

> Won't that break if another process exits at the wrong time?

not if the parent doesn't do any messing with the signal handling. which it doesn't \
need to, as the defaults (and what qprocess does) are perfectly fine. the likely pid \
problem remains. one could wrap only the unregistration, but then a hypothetical race \
between utempter registration calls and unrelated qprocess exits remains.

> I looked at that as well, the issue is finding the correct path for the utempter \
> helper.

the configure test could run 'strings' over libutempter.so and grep for relevant \
patterns. ^^ or just try to divine it from the libutempter location based on typical \
directory structures. the last resort would be letting the user specify it.

> I tried looking briefly at it, but I couldn't quickly find any logind code that did \
> utmp stuff

logind doesn't do the legacy stuff any more (consolekit still did, iirc). you're \
supposed to use loginctl. but i don't know whether one is actually supposed to \
register pseudo ttys in the first place.

> libutempter only supports Linux and FreeBSD

the two dashes were to meant to illustrate a sub-point. i.e., what about non-systemd \
systems?

a whole different approach would be providing an own kutempter - quite similar to \
kcheckpass (which is mostly redundant with pam's unix_chkpwd). or actually, to \
kgrantpty, which is redundant with the pt_chown helper some grantpt() implementations \
use. i actually once had a todo item about that ...


- Oswald


-----------------------------------------------------------
This is an automatically generated e-mail. To reply, visit:
https://git.reviewboard.kde.org/r/128790/#review98742
-----------------------------------------------------------


On Aug. 28, 2016, 1:13 p.m., Martin Tobias Holmedahl Sandsmark wrote:
> 
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> https://git.reviewboard.kde.org/r/128790/
> -----------------------------------------------------------
> 
> (Updated Aug. 28, 2016, 1:13 p.m.)
> 
> 
> Review request for KDE Frameworks, David Faure, Kurt Hindenburg, Rex Dieter, and \
> Thiago Macieira. 
> 
> Bugs: 364779
> https://bugs.kde.org/show_bug.cgi?id=364779
> 
> 
> Repository: kpty
> 
> 
> Description
> -------
> 
> According to the investigation in https://bugs.kde.org/show_bug.cgi?id=364779 \
> utempter does stuff in a way that isn't compatible with \
> QProcess/KProcess/KPtyProcess (calling sigaction() before launching its child \
> process). So remove it, and rely on the fallback methods already implemented. 
> 
> Diffs
> -----
> 
> CMakeLists.txt 3e17cac 
> KF5PtyConfig.cmake.in 66f8c43 
> cmake/FindUTEMPTER.cmake a3ea06a 
> src/CMakeLists.txt caab96f 
> src/ConfigureChecks.cmake ded08f4 
> src/config-pty.h.cmake aaaf8d9 
> src/kpty.cpp 15c3b81 
> 
> Diff: https://git.reviewboard.kde.org/r/128790/diff/
> 
> 
> Testing
> -------
> 
> 
> Thanks,
> 
> Martin Tobias Holmedahl Sandsmark
> 
> 


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<blockquote style="margin-left: 1em; border-left: 2px solid #d0d0d0; padding-left: \
10px;">  <p style="margin-top: 0;">On August 28th, 2016, 1:41 p.m. UTC, <b>Oswald \
Buddenhagen</b> wrote:</p>  <blockquote style="margin-left: 1em; border-left: 2px \
solid #d0d0d0; padding-left: 10px;">  <pre style="white-space: pre-wrap; white-space: \
-moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: \
break-word;"><p style="padding: 0;text-rendering: inherit;margin: 0;line-height: \
inherit;white-space: inherit;">uhm, and why do you think utempter is the preferred \
choice? last time i checked, nobody was shipping konsole setgid utmp. with kdeinit, \
that's not even an option.</p> <p style="padding: 0;text-rendering: inherit;margin: \
0;line-height: inherit;white-space: inherit;">there are several options how to deal \
                with this:
- fork()/wait() around the utempter calls, so it can't mess with the signal handling \
of the current process. though i seem to remmber that the addToUtmp() call actually \
                uses the PID
- re-implement the libutempter calls with QProcess. that's actually how it was \
originally, but was changed because there were incompatible versions of utempter - \
                but that seems like a minor concern compared to the status quo.
- drop utmp handling altogether, as it's been mostly superseded, first by consolekit, \
and now logind. however, respective bindings would have to be actually implemented, \
                and i have no clue how things are supposed to be done. just some dbus \
                calls?
-- what about non-linux systems?</p></pre>
 </blockquote>




 <p>On August 28th, 2016, 1:52 p.m. UTC, <b>Martin Tobias Holmedahl Sandsmark</b> \
wrote:</p>  <blockquote style="margin-left: 1em; border-left: 2px solid #d0d0d0; \
padding-left: 10px;">  <pre style="white-space: pre-wrap; white-space: -moz-pre-wrap; \
white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;"><blockquote \
style="text-rendering: inherit;padding: 0 0 0 1em;border-left: 1px solid \
#bbb;white-space: normal;margin: 0 0 0 0.5em;line-height: inherit;"> <p \
style="padding: 0;text-rendering: inherit;margin: 0;line-height: inherit;white-space: \
inherit;">uhm, and why do you think utempter is the preferred choice? last time i \
checked, nobody was shipping konsole setgid utmp. with kdeinit, that's not even an \
option.</p> </blockquote>
<p style="padding: 0;text-rendering: inherit;margin: 0;line-height: \
inherit;white-space: inherit;">Why is the fallback code there at all, then?</p> \
<blockquote style="text-rendering: inherit;padding: 0 0 0 1em;border-left: 1px solid \
#bbb;white-space: normal;margin: 0 0 0 0.5em;line-height: inherit;"> <ul \
style="padding: 0;text-rendering: inherit;margin: 0 0 0 1em;line-height: \
inherit;white-space: normal;"> <li style="padding: 0;text-rendering: inherit;margin: \
0;line-height: inherit;white-space: normal;">fork()/wait() around the utempter calls, \
so it can't mess with the signal handling of the current process. though i seem to \
remmber that the addToUtmp() call actually uses the PID</li> </ul>
</blockquote>
<p style="padding: 0;text-rendering: inherit;margin: 0;line-height: \
inherit;white-space: inherit;">Won't that break if another process exits at the wrong \
time?</p> <blockquote style="text-rendering: inherit;padding: 0 0 0 1em;border-left: \
1px solid #bbb;white-space: normal;margin: 0 0 0 0.5em;line-height: inherit;"> <ul \
style="padding: 0;text-rendering: inherit;margin: 0 0 0 1em;line-height: \
inherit;white-space: normal;"> <li style="padding: 0;text-rendering: inherit;margin: \
0;line-height: inherit;white-space: normal;">re-implement the libutempter calls with \
QProcess. that's actually how it was originally, but was changed because there were \
incompatible versions of utempter - but that seems like a minor concern compared to \
the status quo.</li> </ul>
</blockquote>
<p style="padding: 0;text-rendering: inherit;margin: 0;line-height: \
inherit;white-space: inherit;">I looked at that as well, the issue is finding the \
correct path for the utempter helper.</p> <blockquote style="text-rendering: \
inherit;padding: 0 0 0 1em;border-left: 1px solid #bbb;white-space: normal;margin: 0 \
0 0 0.5em;line-height: inherit;"> <ul style="padding: 0;text-rendering: \
inherit;margin: 0 0 0 1em;line-height: inherit;white-space: normal;"> <li \
style="padding: 0;text-rendering: inherit;margin: 0;line-height: inherit;white-space: \
normal;">drop utmp handling altogether, as it's been mostly superseded, first by \
consolekit, and now logind. however, respective bindings would have to be actually \
implemented, and i have no clue how things are supposed to be done. just some dbus \
calls?</li> </ul>
</blockquote>
<p style="padding: 0;text-rendering: inherit;margin: 0;line-height: \
inherit;white-space: inherit;">There seems to be a simple dbus call to register with \
logind at least. I tried looking briefly at it, but I couldn't quickly find any \
logind code that did utmp stuff. I didn't look very hard, though.</p> <blockquote \
style="text-rendering: inherit;padding: 0 0 0 1em;border-left: 1px solid \
#bbb;white-space: normal;margin: 0 0 0 0.5em;line-height: inherit;"> <p \
style="padding: 0;text-rendering: inherit;margin: 0;line-height: inherit;white-space: \
inherit;">-- what about non-linux systems?</p> </blockquote>
<p style="padding: 0;text-rendering: inherit;margin: 0;line-height: \
inherit;white-space: inherit;">libutempter only supports Linux and FreeBSD, the \
fallback code seems to at least try to be compatible with other platforms.</p></pre>  \
</blockquote>








</blockquote>

<pre style="white-space: pre-wrap; white-space: -moz-pre-wrap; white-space: \
-pre-wrap; white-space: -o-pre-wrap; word-wrap: break-word;"><blockquote \
style="text-rendering: inherit;padding: 0 0 0 1em;border-left: 1px solid \
#bbb;white-space: normal;margin: 0 0 0 0.5em;line-height: inherit;"> <p \
style="padding: 0;text-rendering: inherit;margin: 0;line-height: inherit;white-space: \
inherit;">Why is the fallback code there at all, then?</p> </blockquote>
<p style="padding: 0;text-rendering: inherit;margin: 0;line-height: \
inherit;white-space: inherit;">it was there first. it will actually work if somebody \
runs konsole as root. which nobody does, of course.</p> <blockquote \
style="text-rendering: inherit;padding: 0 0 0 1em;border-left: 1px solid \
#bbb;white-space: normal;margin: 0 0 0 0.5em;line-height: inherit;"> <p \
style="padding: 0;text-rendering: inherit;margin: 0;line-height: inherit;white-space: \
inherit;">Won't that break if another process exits at the wrong time?</p> \
</blockquote> <p style="padding: 0;text-rendering: inherit;margin: 0;line-height: \
inherit;white-space: inherit;">not if the parent doesn't do any messing with the \
signal handling. which it doesn't need to, as the defaults (and what qprocess does) \
are perfectly fine. the likely pid problem remains. one could wrap only the \
unregistration, but then a hypothetical race between utempter registration calls and \
unrelated qprocess exits remains.</p> <blockquote style="text-rendering: \
inherit;padding: 0 0 0 1em;border-left: 1px solid #bbb;white-space: normal;margin: 0 \
0 0 0.5em;line-height: inherit;"> <p style="padding: 0;text-rendering: \
inherit;margin: 0;line-height: inherit;white-space: inherit;">I looked at that as \
well, the issue is finding the correct path for the utempter helper.</p> \
</blockquote> <p style="padding: 0;text-rendering: inherit;margin: 0;line-height: \
inherit;white-space: inherit;">the configure test could run 'strings' over \
libutempter.so and grep for relevant patterns. ^^ or just try to divine it from the \
libutempter location based on typical directory structures. the last resort would be \
letting the user specify it.</p> <blockquote style="text-rendering: inherit;padding: \
0 0 0 1em;border-left: 1px solid #bbb;white-space: normal;margin: 0 0 0 \
0.5em;line-height: inherit;"> <p style="padding: 0;text-rendering: inherit;margin: \
0;line-height: inherit;white-space: inherit;">I tried looking briefly at it, but I \
couldn't quickly find any logind code that did utmp stuff</p> </blockquote>
<p style="padding: 0;text-rendering: inherit;margin: 0;line-height: \
inherit;white-space: inherit;">logind doesn't do the legacy stuff any more \
(consolekit still did, iirc). you're supposed to use loginctl. but i don't know \
whether one is actually supposed to register pseudo ttys in the first place.</p> \
<blockquote style="text-rendering: inherit;padding: 0 0 0 1em;border-left: 1px solid \
#bbb;white-space: normal;margin: 0 0 0 0.5em;line-height: inherit;"> <p \
style="padding: 0;text-rendering: inherit;margin: 0;line-height: inherit;white-space: \
inherit;">libutempter only supports Linux and FreeBSD</p> </blockquote>
<p style="padding: 0;text-rendering: inherit;margin: 0;line-height: \
inherit;white-space: inherit;">the two dashes were to meant to illustrate a \
sub-point. i.e., what about non-systemd systems?</p> <p style="padding: \
0;text-rendering: inherit;margin: 0;line-height: inherit;white-space: inherit;">a \
whole different approach would be providing an own kutempter - quite similar to \
kcheckpass (which is mostly redundant with pam's unix_chkpwd). or actually, to \
kgrantpty, which is redundant with the pt_chown helper some grantpt() implementations \
use. i actually once had a todo item about that ...</p></pre>
<br />










<p>- Oswald</p>


<br />
<p>On August 28th, 2016, 1:13 p.m. UTC, Martin Tobias Holmedahl Sandsmark wrote:</p>








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<div>Review request for KDE Frameworks, David Faure, Kurt Hindenburg, Rex Dieter, and \
Thiago Macieira.</div> <div>By Martin Tobias Holmedahl Sandsmark.</div>


<p style="color: grey;"><i>Updated Aug. 28, 2016, 1:13 p.m.</i></p>







<div style="margin-top: 1.5em;">
 <b style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Bugs: </b>


 <a href="https://bugs.kde.org/show_bug.cgi?id=364779">364779</a>


</div>



<div style="margin-top: 1.5em;">
 <b style="color: #575012; font-size: 10pt;">Repository: </b>
kpty
</div>


<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Description </h1>
 <table width="100%" bgcolor="#ffffff" cellspacing="0" cellpadding="10" \
style="border: 1px solid #b8b5a0">  <tr>
  <td>
   <pre style="margin: 0; padding: 0; white-space: pre-wrap; white-space: \
-moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: \
break-word;"><p style="padding: 0;text-rendering: inherit;margin: 0;line-height: \
inherit;white-space: inherit;">According to the investigation in \
https://bugs.kde.org/show_bug.cgi?id=364779 utempter does stuff in a way that isn't \
compatible with QProcess/KProcess/KPtyProcess (calling sigaction() before launching \
its child process). So remove it, and rely on the fallback methods already \
implemented.</p></pre>  </td>
 </tr>
</table>



<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Diffs</b> </h1>
<ul style="margin-left: 3em; padding-left: 0;">

 <li>CMakeLists.txt <span style="color: grey">(3e17cac)</span></li>

 <li>KF5PtyConfig.cmake.in <span style="color: grey">(66f8c43)</span></li>

 <li>cmake/FindUTEMPTER.cmake <span style="color: grey">(a3ea06a)</span></li>

 <li>src/CMakeLists.txt <span style="color: grey">(caab96f)</span></li>

 <li>src/ConfigureChecks.cmake <span style="color: grey">(ded08f4)</span></li>

 <li>src/config-pty.h.cmake <span style="color: grey">(aaaf8d9)</span></li>

 <li>src/kpty.cpp <span style="color: grey">(15c3b81)</span></li>

</ul>

<p><a href="https://git.reviewboard.kde.org/r/128790/diff/" style="margin-left: \
3em;">View Diff</a></p>






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