[Bug 1669578] Re: Get ttyname() to work properly in containers

[LocutusOfBorg via ubuntu-bugs]

@Jose Manuel Santamaria Lema (panfaust)

can you please send the patch upstream so they integrate it in a new release?
We don't get emails for bugs that are closed, and I don't understand the need 
of an Ubuntu only patch.
I can sponsor once you report and get it acked by upstream.

G.

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Launchpad Bug Tracker]

Status changed to 'Confirmed' because the bug affects multiple users.

** Changed in: multitail (Ubuntu)
   Status: New => Confirmed

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Jose Manuel Santamaria Lema]

Here's a possible fix. I tested it on bionic and it seems it works. For
my xenial machines I had to workaround it disabling completely the check
because the glibc there doesn't behave the same way.

So I'm attaching a debdiff with the proposed upload for bionic; it would
be nice if someone could sponsor it, thanks in advance.

** Patch added: "multitail -fix for ttyname() based check"
   
https://bugs.launchpad.net/ubuntu/+source/multitail/+bug/1669578/+attachment/5061383/+files/multitail_fix.diff

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Jose Manuel Santamaria Lema]

Hello,

I got this problem also in multitail but I think I know how to patch it.
I will attach the debdiff as soon as I can test it properly.

** Also affects: multitail (Ubuntu)
   Importance: Undecided
   Status: New

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Christian Brauner]

Wohoo, great job gentleman. :)

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Axel Beckert]

So the screen testsuite I wrote 2.5 years ago actually found a bug?
Cool! :-)

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[LocutusOfBorg]

yeah :)

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Launchpad Bug Tracker]

This bug was fixed in the package screen - 4.5.1-3ubuntu2

---
screen (4.5.1-3ubuntu2) artful; urgency=medium

  [ Christian Brauner ]
  * debian/patches/0001-screen-don-t-stat.patch:
- fix testsuite error when tty is ""

 -- Gianfranco Costamagna   Wed, 10 May 2017
16:59:10 +0200

** Changed in: screen (Ubuntu)
   Status: Fix Committed => Fix Released

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[LocutusOfBorg]

lets see if now this bug gets closed :)

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Christian Brauner]

Patch send to upstream as well.

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Christian Brauner]

@LocutusOfBorg, the patch I appended is applicable directly to the deb
source used in the package.

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Christian Brauner]

@LocutusOfBorg, thanks for taking a close look at this. Found the bug.
I'm appending a patch that fixes it and makes the autopkgtestsuite pass
for me!

** Patch added: "0001-screen-don-t-stat.patch"
   
https://bugs.launchpad.net/ubuntu/+source/glibc/+bug/1669578/+attachment/4874713/+files/0001-screen-don-t-stat.patch

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[LocutusOfBorg]

I did get the same result (pbuilder artful clean environment)
I also did try to reproduce autopkgtestsuite in an lxc container and the test 
has failed

sudo autopkgtest-build-lxc ubuntu artful
autopkgtest --shell-fail --apt-upgrade screen_4.5.1-3ubuntu1.dsc -- lxc --sudo 
autopkgtest-artful

the problem is that when the test fails, you get a shell inside the container, 
and prove -v debian/tests/t works there :(
culprit might be that screen -X and screen -Q stopped working

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Christian Brauner]

Hm, the test all pass locally for me

So I downloaded the package
https://launchpad.net/ubuntu/+archive/primary/+files/screen_4.5.1-3ubuntu1_amd64.deb
from the proposed https://launchpad.net/ubuntu/+source/screen repo and
ran the tests locally and get:

chb@conventiont|~/mnt/C/screen-debian
> screen --version
Screen version 4.05.01 (GNU) 25-Feb-17
chb@conventiont|~/mnt/C/screen-debian
> cd screen-4.5.1/debian/tests/t/
chb@conventiont|~/mnt/C/screen-debian/screen-4.5.1/debian/tests/t
> ls -a
.   boilerplate.sh  create-list-quit.t  dash-U.t
..  command.t   dash-Dm.t   version-help.t
chb@conventiont|~/mnt/C/screen-debian/screen-4.5.1/debian/tests/t
> ./command.t
1..4
ok 1 - Create session
ok 2 - Detached session found
ok 3 - Session has expected session name
ok 4 - Session is gone
chb@conventiont|~/mnt/C/screen-debian/screen-4.5.1/debian/tests/t
> ./create-list-quit.t
1..6
ok 1 - Create session
ok 2 - Detached session found
ok 3 - Session has expected session name
ok 4 - Session has a window with id 0
ok 5 - Quit command sent to session
ok 6 - Session is gone
chb@conventiont|~/mnt/C/screen-debian/screen-4.5.1/debian/tests/t
> ./dash-Dm.t
1..5
ok 1 - Create session
ok 2 - Detached session found
ok 3 - Session has expected session name
ok 4 - Quit command sent to session
ok 5 - Session is gone
chb@conventiont|~/mnt/C/screen-debian/screen-4.5.1/debian/tests/t
> ./dash-U.t
1..6
ok 1 - Create session
ok 2 - Detached session found
ok 3 - Session has expected session name
ok 4 - Session has a window with id 0
ok 5 - Quit command sent to session
ok 6 - Session is gone
chb@conventiont|~/mnt/C/screen-debian/screen-4.5.1/debian/tests/t
> ./version-help.t
1..2
ok 1 - Outputs version
ok 2 - Outputs help

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Christian Brauner]

@LocutusOfBorg, thanks for sponsoring I'm looking into it.

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[LocutusOfBorg]

@Christian, I sponsored it, but it fails the testsuite
http://autopkgtest.ubuntu.com/packages/screen

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Re: [Bug 1669578] Re: Get ttyname() to work properly in containers

[Christian Brauner]

On Fri, May 05, 2017 at 05:04:18PM -, LocutusOfBorg wrote:
> >If you're referring to screen . The screen version right now with my
> >compat-layer patch applied
> >should be fully backwards compatible.
> 
> so, you mean, it didn't work before and still doesn't work with older
> glibc?

TL;DR: It should all work now without any regression
   potential. I tested your package with my patches
   applied and it works fine inside and outside of
   containers.

Additional info to summarize again what has been said in
the thread above:
1. For screen to work in containers you need a specific
   patch that Serge and I have successfully pushed into
   glibc upstream and which is already available in the
   glibc package for Ubuntu 17.04 and 17.10.
   - The glibc patch has no effect whatsoever of screen
 outside of containers.
   - The glibc patch is fully backwards compatible to
 any program out there and does not lead to
 regressions.

2. For screen to work in containers you also need the
   three patches that I wrote and pushed to upstream
   screen and which you now applied in your package.
   Thanks for that!
   - Downstream screen in {Debian,Ubuntu} communicates
 using FIFOs whereas newer upstream versions of screen
 use unix domain sockets. So far these two things have
 been mutually exclusive. However, I wrote a compat
 layer that allows screen to use both. This is my
 third patch which is also available upstream
 and now in your package.

3. **Orthogonal to all of this** I wanted to direct the
   attention of the screen maintainers to the fact that
   upstream screen uses a message protocol which is based
   on C struct that is either send around via the FIFO or
   the unix domain socket. This message protocol is
   versioned using a simple integer numbering scheme
   {1,2,3,4,5, ...}. Changing this message protocol
   is essentially an ABI break if you want to call it that.
   This means, clients that send a C struct using a
   different version than an already running screen server
   will not be able to attach to already existing sessions.
   This scenario can be postponed but it will happen once
   the screen 4.*.* series {Debian,Ubuntu} ends. There is
   no way to fix this that I know of. I just wanted to
   point this out and make the maintainers aware that
   on the next possible version bump for screen it would
   cause a break in backwards compatibility.

> 
> -- 
> You received this bug notification because you are subscribed to the bug
> report.
> https://bugs.launchpad.net/bugs/1669578
> 
> Title:
>   Get ttyname() to work properly in containers
> 
> Status in glibc package in Ubuntu:
>   Fix Released
> Status in screen package in Ubuntu:
>   Fix Committed
> Status in tmux package in Ubuntu:
>   Fix Released
> 
> Bug description:
>   For the past year or so, the LXD team has been trying to resolve an
>   issue affecting screen, tmux and a bunch of other software (including
>   the "tty" command).
> 
>   The problem comes from the fact that when attaching to a container,
>   your terminal's pts device comes from the host and therefore can't be
>   found in /dev/pts/.
> 
>   glibc makes the assumption that it can readlink /proc/self/fd/0 and
>   that the target path will exist. This simply isn't true as the symlink
>   target returned by the kernel, is confusingly relative to the host's
>   root and not the container's.
> 
>   Which means that if the target happens to exist, it's actually going
>   to be an entirely different pts device from the one that you're
>   actually attached to.
> 
>   
>   You therefore need to do something along the lines of:
>- Resolve the symlink. If the target doesn't exist, return the symlink as 
> the ttyname.
>- If the target does exist, check that its major and minor matches that of 
> the symlink itself, if it doesn't, then return the symlink rather than the 
> target.
> 
>   
>   That's the ideal approach which makes existing software keep working 
> properly without the need for any added code. After about a year of 
> bikeshedding, the proposed glibc upstream fix has now evolved to instead 
> returning ENODEV in the is_pty function. This allows downstream glibc users 
> to detect this case and then use /proc/self/fd/0 rather than the return value 
> of ttyname() but means every software using ttyname() now needs fixing.
> 
>   As we very much care about Ubuntu running properly inside LXD
>   containers, our suggested patchset includes both the ENODEV patch as
>   is still being considered by upstream (stuck on legal validation) AND
>   another patch which has ttyname() return the symlink when it receives
>   the ENODEV.
> 
>   
>   We feel this is the best way to fix the problem entirely right now. Once 
> glibc upstream merges the ENODEV side of this and all affected software get 
> fixed upstream to deal with it, we'll then be able to drop that patch without 
> causing any regressions.
> 
> To manage 

[Bug 1669578] Re: Get ttyname() to work properly in containers

[LocutusOfBorg]

>If you're referring to screen . The screen version right now with my
>compat-layer patch applied
>should be fully backwards compatible.

so, you mean, it didn't work before and still doesn't work with older
glibc?

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Re: [Bug 1669578] Re: Get ttyname() to work properly in containers

[Christian Brauner]

On Fri, May 5, 2017 at 4:57 PM, LocutusOfBorg
 wrote:
> I don't think we should upload without having retro-compatibility with
> older and still supported Ubuntu releases.

What are you referring to now? The glibc patch? That doesn't break
anything otherwise
glibc upstream would have yelled at us.

If you're referring to screen . The screen version right now with my
compat-layer patch applied
should be fully backwards compatible.

>
> --
> You received this bug notification because you are subscribed to the bug
> report.
> https://bugs.launchpad.net/bugs/1669578
>
> Title:
>   Get ttyname() to work properly in containers
>
> Status in glibc package in Ubuntu:
>   Fix Released
> Status in screen package in Ubuntu:
>   Fix Committed
> Status in tmux package in Ubuntu:
>   Fix Released
>
> Bug description:
>   For the past year or so, the LXD team has been trying to resolve an
>   issue affecting screen, tmux and a bunch of other software (including
>   the "tty" command).
>
>   The problem comes from the fact that when attaching to a container,
>   your terminal's pts device comes from the host and therefore can't be
>   found in /dev/pts/.
>
>   glibc makes the assumption that it can readlink /proc/self/fd/0 and
>   that the target path will exist. This simply isn't true as the symlink
>   target returned by the kernel, is confusingly relative to the host's
>   root and not the container's.
>
>   Which means that if the target happens to exist, it's actually going
>   to be an entirely different pts device from the one that you're
>   actually attached to.
>
>
>   You therefore need to do something along the lines of:
>- Resolve the symlink. If the target doesn't exist, return the symlink as 
> the ttyname.
>- If the target does exist, check that its major and minor matches that of 
> the symlink itself, if it doesn't, then return the symlink rather than the 
> target.
>
>
>   That's the ideal approach which makes existing software keep working 
> properly without the need for any added code. After about a year of 
> bikeshedding, the proposed glibc upstream fix has now evolved to instead 
> returning ENODEV in the is_pty function. This allows downstream glibc users 
> to detect this case and then use /proc/self/fd/0 rather than the return value 
> of ttyname() but means every software using ttyname() now needs fixing.
>
>   As we very much care about Ubuntu running properly inside LXD
>   containers, our suggested patchset includes both the ENODEV patch as
>   is still being considered by upstream (stuck on legal validation) AND
>   another patch which has ttyname() return the symlink when it receives
>   the ENODEV.
>
>
>   We feel this is the best way to fix the problem entirely right now. Once 
> glibc upstream merges the ENODEV side of this and all affected software get 
> fixed upstream to deal with it, we'll then be able to drop that patch without 
> causing any regressions.
>
> To manage notifications about this bug go to:
> https://bugs.launchpad.net/ubuntu/+source/glibc/+bug/1669578/+subscriptions

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[LocutusOfBorg]

I don't think we should upload without having retro-compatibility with
older and still supported Ubuntu releases.

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Re: [Bug 1669578] Re: Get ttyname() to work properly in containers

[Christian Brauner]

On Fri, May 5, 2017 at 1:34 PM, Christian Brauner
 wrote:
> On Fri, May 5, 2017 at 12:40 PM, Christian Brauner
>  wrote:
>> This version of screen doesn't work in containers for me anymore.
>
> @LocutusOfBorg, nevermind I tested this on Xenial which doesn't seem
> to come with a version of glibc the path that Serge and I wrote. The
> screen version you built with my patches included work on patched
> glibc versions inside containers. From my testing with the version you
> build including my patches attaching to older fifo-based screen
> sessions works and new ones are all socket-based. Thanks!

Fwiw, I'd like to see the glibc patch Serge and I wrote SRUed into Xenial
(and if not already done) glibc since this is likely what most users currently
use as images in their containers. @Adam, is this something we can do?

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Re: [Bug 1669578] Re: Get ttyname() to work properly in containers

[Christian Brauner]

On Fri, May 5, 2017 at 12:40 PM, Christian Brauner
 wrote:
> This version of screen doesn't work in containers for me anymore.

@LocutusOfBorg, nevermind I tested this on Xenial which doesn't seem
to come with a version of glibc the path that Serge and I wrote. The
screen version you built with my patches included work on patched
glibc versions inside containers. From my testing with the version you
build including my patches attaching to older fifo-based screen
sessions works and new ones are all socket-based. Thanks!

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Re: [Bug 1669578] Re: Get ttyname() to work properly in containers

[Christian Brauner]

This version of screen doesn't work in containers for me anymore.

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[LocutusOfBorg]

I had to tweak the upstream commits, because they weren't applying on top of 
Debian changes, and uploaded  the following in my ppa.
https://launchpad.net/~costamagnagianfranco/+archive/ubuntu/locutusofborg-ppa/+sourcepub/7773744/+listing-archive-extra

can you please test it?

** Patch added: 
"0001-Add-patches-to-make-Get-ttyname-work-properly-in-con.patch"
   
https://bugs.launchpad.net/ubuntu/+source/glibc/+bug/1669578/+attachment/4872175/+files/0001-Add-patches-to-make-Get-ttyname-work-properly-in-con.patch

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  Get ttyname() to work properly in containers

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Christian Brauner]

@LocutusOfBorg, can you please tell me exactly what you need? From
looking at

git clone https://anonscm.debian.org/git/collab-maint/screen.git
git checkout debian/4.5.1-3

none of the patches that I've pushed upstream are available in this repo.
For this to work you'd need:

1.
commit 78d2a73273786bd7c5f3be481b23a5bee19dc519
Author: Christian Brauner 
Date:   Wed Mar 22 18:16:52 2017 +0100

handle pty device from different namespace

Various programs that deal with namespaces will use pty devices that exist 
in
another namespace. One obvious candiate are containers. So far ttyname() was
incorrectly handling this case because the pts device stems from the host 
and
thus cannot be found amongst the current namespace's /dev/pts/ entries.
Serge Hallyn and I recently upstreamed patches to glibc that allow 
ttyname{_r}()
to correctly handle this case. At a minimum, ttyname{_r}() will set errno to
ENODEV in case it finds that the /dev/pts/ device that the symlink 
points to
exists in another namespace. This commit will allow screen to handle this 
case
and behave correctly in a container.

Signed-off-by: Christian Brauner 

2.commit 7e755ed62d311b00102b053eee88359bbf8ac2df
Author: Christian Brauner 
Date:   Wed Apr 5 14:24:22 2017 +0200

screen: handle pts devices in different namespaces

Various programs that deal with namespaces will use pty devices that exist 
in
another namespace. One obvious candidate are containers. So far ttyname() 
was
incorrectly handling this case because the pts device stems from the host 
and
thus cannot be found amongst the current namespace's /dev/pts/ entries.
Serge Hallyn and I recently upstreamed patches to glibc that allow 
ttyname{_r}()
to correctly handle this case. At a minimum, ttyname{_r}() will set errno to
ENODEV in case it finds that the /dev/pts/ device that the symlink 
points to
exists in another namespace.

(The next comment is a little longer but tries to ensure that one can still
understand what is going on after some time has passed.)
In case we detect that ttyname{_r}() returns NULL and sets errno to ENODEV 
we
have ample reason to assume that the pts device exists in a different
namespace. In this case, the code will set a global flag indicating this 
case
to true. Furthermore, all operations (e.g. chmod(), chown(), etc.) will now
need to operate on the symbolic link /proc/self/fd/0 directly. While this
sounds straightforward, it becomes difficult to handle this case correctly 
when
we reattach to an already existing screen session from a different pts 
device
than the original one. Let's look at the general reattach logic a little
closer:

Assume we are running a shell that uses a pts device from a different
namespace:

root@zest1:~# ls -al /proc/self/fd/
total 0
dr-x-- 2 root root  0 Apr  2 20:22 .
dr-xr-xr-x 9 root root  0 Apr  2 20:22 ..
lrwx-- 1 root root 64 Apr  2 20:22 0 -> /dev/pts/6
lrwx-- 1 root root 64 Apr  2 20:22 1 -> /dev/pts/6
lrwx-- 1 root root 64 Apr  2 20:22 2 -> /dev/pts/6
l-wx-- 1 root root 64 Apr  2 20:22 3 -> pipe:[3067913]
lr-x-- 1 root root 64 Apr  2 20:22 4 -> /proc/27413/fd
lrwx-- 1 root root 64 Apr  2 20:22 9 -> socket:[32944]

root@zest1:~# ls -al /dev/pts/
total 0
drwxr-xr-x 2 root root  0 Mar 30 17:55 .
drwxr-xr-x 8 root root580 Mar 30 17:55 ..
crw--w 1 root tty  136, 0 Mar 30 17:55 0
crw--w 1 root tty  136, 1 Mar 30 17:55 1
crw--w 1 root tty  136, 2 Mar 30 17:55 2
crw--w 1 root tty  136, 3 Mar 30 17:55 3
crw--w 1 root tty  136, 4 Mar 30 17:55 4
crw-rw-rw- 1 root root   5, 2 Apr  2 20:22 ptmx

(As one can see /dev/pts/6 does not exist in the current namespace.)
Now, start a screen session in this shell. In this case this patch will have
screen directly operate on /proc/self/fd/0.
Let's look at the attach case. When we attach to an existing screen session
where the associated pts device lives in another namespace we need a way to
uniquely identify the pts device that is used and also need a way to get a
valid fd when we need one. This patch solves this by ensuring that a valid 
file
descriptor to the pts device is sent via a unix socket and SCM_RIGHTS to the
socket and display handling part of screen. However, screen also sends 
around
the name of the associated pts device or, in the case where the pts device
exists in another namespace, the symlink /proc/self/fd/0. But after having 
sent
the fd this part of the codebase cannot simply operate on /proc/self/fd/0 
since
it 

[Bug 1669578] Re: Get ttyname() to work properly in containers

[Christian Brauner]

@LocutusOfBorg, I can give you a screen 4-5.1-3 compatible patch based on the 
Debian package.
One thing to note is that even my compat-layer patch will be of no help once 
{Debian,Ubuntu} breaks the message protocol which they eventually *will* have 
to do. Upstream screen uses at least message version 5 whereas {Debian,Ubuntu} 
use message version 2. Once you bump the message version previous screen 
versions will break. But updating the message protocol will be unavoidable in 
the long run. So you should consider warning users and start breaking backward 
compatibility at some point in the near future. :)

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[LocutusOfBorg]

@cbrauner, do you have a patch that needs sponsoring?
We are discussing merging 4.5.1-3 from Debian experimental, but your patch 
can't apply

e.g. we have no tty.c and tty.h in our packaging.

Feel free to upload in a ppa or a patch here and I'll look/sponsor it
(anybody is free to steal the packaging from me)

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Christian Brauner]

I sent a patch to musl upstream to align them with glibc. The patch is
merged: https://git.musl-
libc.org/cgit/musl/commit/?id=e1232f5b5185e8f337806841018369407e32e77d .

** Also affects: musl (Ubuntu)
   Importance: Undecided
   Status: New

** No longer affects: musl (Ubuntu)

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Christian Brauner]

An upstream-compatible version of 0001-add-compat-layer-to-handle-both-
fifos-and-sockets.patch is now merged upstream into screen v4. See
https://lists.gnu.org/archive/html/screen-devel/2017-04/msg00023.html .

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Launchpad Bug Tracker]

This bug was fixed in the package glibc - 2.24-9ubuntu2

---
glibc (2.24-9ubuntu2) zesty; urgency=medium

  * debian/patches/any/cvs-resolv-internal-qtype.diff: Revert to avoid
failure in name resolution on upgrades from yakkety (LP: #1674532)

 -- Adam Conrad   Tue, 21 Mar 2017 15:27:15 -0600

** Changed in: glibc (Ubuntu)
   Status: Fix Committed => Fix Released

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Christian Brauner]

Updated version of fifo-socket-compat patch that removes left-behind
debugging statement.

** Patch added: "0001-add-compat-layer-to-handle-both-fifos-and-sockets.patch"
   
https://bugs.launchpad.net/ubuntu/+source/glibc/+bug/1669578/+attachment/4857526/+files/0001-add-compat-layer-to-handle-both-fifos-and-sockets.patch

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Christian Brauner]

I tested the screen-fifo-socket compatibility patch here
https://asciinema.org/a/111692 .

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Christian Brauner]

So, Stéphane brought to my attention that we're not including the patch
because it switches screen to use sockets instead of fifos and thus
makes it impossible to switch to existing fifo-based screen sessions.
I've written a patch that adds a compatibility layer to support both
fifo-based and socket-based screen sessions. The idea is to only re-use
existing fifo-sessions but never create new ones. All new screen
sessions will be socket-based.

** Patch added: "0001-add-compat-layer-to-handle-both-fifos-and-sockets.patch"
   
https://bugs.launchpad.net/ubuntu/+source/glibc/+bug/1669578/+attachment/4857205/+files/0001-add-compat-layer-to-handle-both-fifos-and-sockets.patch

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Christian Brauner]

The screen patch is now also upstream
http://git.savannah.gnu.org/cgit/screen.git/commit/?id=565b8901cad828d921038cd6235501c42d1c9a32
. @stgraber, did you get around to pushing to to the archive as well so
that we can land this in zesty?

** Changed in: screen (Ubuntu)
   Status: In Progress => Fix Committed

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Christian Brauner]

The tmux patch is now also upstream.

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Christian Brauner]

Since the Ubuntu screen package was synced with Debian yesterday the
attached patch does not apply cleanly anymore. So here's a new version
of it that also is much closer to what I've pushed upstream.

** Patch added: "0001-screen-handle-pts-devices-in-different-namespaces.patch"
   
https://bugs.launchpad.net/ubuntu/+source/glibc/+bug/1669578/+attachment/4855341/+files/0001-screen-handle-pts-devices-in-different-namespaces.patch

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Christian Brauner]

** Changed in: tmux (Ubuntu)
   Status: In Progress => Fix Released

** Changed in: screen (Ubuntu)
   Status: Fix Released => In Progress

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Launchpad Bug Tracker]

This bug was fixed in the package screen - 4.5.0-5ubuntu1

---
screen (4.5.0-5ubuntu1) zesty; urgency=low

  * Merge from Debian unstable.  Remaining changes:
- 83_handle_pty_device_namespace.patch (LP: #1669578)

 -- Gianfranco Costamagna   Tue, 04 Apr 2017
12:54:26 +0200

** Changed in: screen (Ubuntu)
   Status: In Progress => Fix Released

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Christian Brauner]

Here's a patch for the current tmux version of Ubuntu. We should get
this sorted before this Thursday.

** Patch added: "0001-handle-pty-devices-in-different-namespaces.patch"
   
https://bugs.launchpad.net/ubuntu/+source/glibc/+bug/1669578/+attachment/4854344/+files/0001-handle-pty-devices-in-different-namespaces.patch

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Christian Brauner]

About the tmux patch. Nicholas plans to merge a patch that is nearly
identical into tmux master sometime next week but this might be too late
for final freeze.

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Christian Brauner]

** Changed in: tmux (Ubuntu)
   Status: Triaged => In Progress

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Christian Brauner]

Here's an updated version of the patch and a comment explaining in a
little more detail what is happening:

Subject: [PATCH] screen: handle pts devices in different namespaces

Various programs that deal with namespaces will use pty devices that exist in
another namespace. One obvious candiate are containers. So far ttyname() was
incorrectly handling this case because the pts device stems from the host and
thus cannot be found amongst the current namespace's /dev/pts/ entries.
Serge Hallyn and I recently upstreamed patches to glibc that allow
ttyname{_r}() to correctly handle this case. At a minimum, ttyname{_r}() will
set errno to ENODEV in case it finds that the /dev/pts/ device that the
symlink points to exists in another namespace.

(The next comment is a little longer but tries to ensure that one can still
understand what is going on after some time has passed.)
In case we detect that ttyname{_r}() returns NULL and sets errno to ENODEV we
have ample reason to assume that the pts device exists in a different
namespace. In this case, the code will set a global flag indicating this case
to true. Furthermore, all operations (e.g. chmod(), chown(), etc.) will now
need to operate on the symbolic link /proc/self/fd/0 directly. While this
sounds straightforward, it becomes difficult to handle this case correctly when
we reattach to an already existing screen session from a different pts device
than the original one. Let's look at the general reattach logic a little
closer:

Assume we are running a shell that uses a pts device from a different
namespace:

root@zest1:~# ls -al /proc/self/fd/
total 0
dr-x-- 2 root root  0 Apr  2 20:22 .
dr-xr-xr-x 9 root root  0 Apr  2 20:22 ..
lrwx-- 1 root root 64 Apr  2 20:22 0 -> /dev/pts/6
lrwx-- 1 root root 64 Apr  2 20:22 1 -> /dev/pts/6
lrwx-- 1 root root 64 Apr  2 20:22 2 -> /dev/pts/6
l-wx-- 1 root root 64 Apr  2 20:22 3 -> pipe:[3067913]
lr-x-- 1 root root 64 Apr  2 20:22 4 -> /proc/27413/fd
lrwx-- 1 root root 64 Apr  2 20:22 9 -> socket:[32944]

root@zest1:~# ls -al /dev/pts/
total 0
drwxr-xr-x 2 root root  0 Mar 30 17:55 .
drwxr-xr-x 8 root root580 Mar 30 17:55 ..
crw--w 1 root tty  136, 0 Mar 30 17:55 0
crw--w 1 root tty  136, 1 Mar 30 17:55 1
crw--w 1 root tty  136, 2 Mar 30 17:55 2
crw--w 1 root tty  136, 3 Mar 30 17:55 3
crw--w 1 root tty  136, 4 Mar 30 17:55 4
crw-rw-rw- 1 root root   5, 2 Apr  2 20:22 ptmx

(As one can see /dev/pts/6 does not exist in the current namespace.)
Now, start a screen session in this shell. In this case this patch will have
screen directly operate on /proc/self/fd/0.
Let's look at the attach case. When we attach to an existing screen session
where the associated pts device lives in another namespace we need a way to
uniquely identify the pts device that is used and also need a way to get a
valid fd when we need one. This patch solves this by ensuring that a valid file
descriptor to the pts device is sent via a unix socket and SCM_RIGHTS to the
socket and display handling part of screen. However, screen also sends around
the name of the associated pts device or, in the case where the pts device
exists in another namespace, the symlink /proc/self/fd/0. But after having sent
the fd this part of the codebase cannot simply operate on /proc/self/fd/0 since
it very likely refers to a different file. So we need to operate on
/proc/self/fd/ but also need to ensure that we haven't
been tricked into operating on a tampered with file or device. So we cannot
simply sent /proc/self/fd/0 via the unix socket. Instead we read the contents
of the symbolic link /proc/self/fd/0 in the main function and sent it via the
unix socket. Then in the socket and display handling part of screen, we read
the contents of the /proc/self/fd/ as well and compare
the pts device names. If they match we know that everything is well. However,
now we also need to update any tty handling code to directly operate on
/proc/self/fd/.

** Patch added: "0001-screen-handle-pts-devices-in-different-namespaces.patch"
   
https://bugs.launchpad.net/ubuntu/+source/glibc/+bug/1669578/+attachment/4853022/+files/0001-screen-handle-pts-devices-in-different-namespaces.patch

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Re: [Bug 1669578] Re: Get ttyname() to work properly in containers

[Christian Brauner]

I'll likely add another patch to this soon to handle some more corner-
cases.

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Christian Brauner]

Here's a patch for screen that got things working for me. I've tested
screen startup and various ways of attach (screen -r, screen -rx, and
screen -rxD). Would be nice if people are able to test this. So if we
could get it into proposed that be +1. The patch in its current form is
directly applicable to the screen-4.5.0 Ubuntu sources. Once we consider
it to be fine I will prepare a patch for master and sent it out to
upstream.

** Patch added: "0001-screen-handle-pts-devices-in-different-namespaces.patch"
   
https://bugs.launchpad.net/ubuntu/+source/glibc/+bug/1669578/+attachment/4851595/+files/0001-screen-handle-pts-devices-in-different-namespaces.patch

** Changed in: screen (Ubuntu)
   Status: Fix Released => In Progress

** Changed in: screen (Ubuntu)
 Assignee: Stéphane Graber (stgraber) => Christian Brauner (cbrauner)

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Christian Brauner]

So aside from the Ubuntu package being outdated (The codebase has indeed
changed massively.) the patch we need to get screen working properly is
way more intrusive then originally thought and there might even be the
case that we have to do some additional lower-level plumbing in the
kernel or glibc to get this working. In short, screen tries to perform
various operations on the corresponding /dev/pts/ paths that the
symbolic links under /proc/self/fd/ point to and it is not clear
whether we can support all of that by just using the symlinks
themselves.

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Re: [Bug 1669578] Re: Get ttyname() to work properly in containers

[Axel Beckert]

Hi Michael,

Michael Sparmann wrote:
> That ifndef has been removed from upstream code in
> http://git.savannah.gnu.org/cgit/screen.git/commit/?id=d965ff1d92e2bd57d24b68cfbd6990486024baa3
> almost 2 years ago, but that apparently hasn't landed in the ubuntu
> package yet.

That commit is only present in the master branch which is the
developement branch for a potential Screen 5.x series.

But that branch iss far from stable. Debian and Ubuntu currently track
the screen-v4 stable branch — which still has that code.

Regards, Axel
-- 
 ,''`.  |  Axel Beckert , http://people.debian.org/~abe/
: :' :  |  Debian Developer, ftp.ch.debian.org Admin
`. `'   |  4096R: 2517 B724 C5F6 CA99 5329  6E61 2FF9 CD59 6126 16B5
  `-|  1024D: F067 EA27 26B9 C3FC 1486  202E C09E 1D89 9593 0EDE

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  Get ttyname() to work properly in containers

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Michael Sparmann]

The fix does not seem to work, it just changes the error message to "Cannot 
open your terminal '' - please check." for me.
The reason seems to be that the patch relies on attach_fd to be set by code 
that's inside an ifndef NAMEDPIPE block, which isn't being compiled for the 
ubuntu package.
That ifndef has been removed from upstream code in 
http://git.savannah.gnu.org/cgit/screen.git/commit/?id=d965ff1d92e2bd57d24b68cfbd6990486024baa3
 almost 2 years ago, but that apparently hasn't landed in the ubuntu package 
yet.

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  Get ttyname() to work properly in containers

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Launchpad Bug Tracker]

This bug was fixed in the package screen - 4.5.0-3ubuntu1

---
screen (4.5.0-3ubuntu1) zesty; urgency=medium

  * Cherry-pick bugfix for screen in containers:
- 83_handle_pty_device_namespace.patch (LP: #1669578)

 -- Stéphane Graber   Fri, 24 Mar 2017 14:35:41
-0400

** Changed in: screen (Ubuntu)
   Status: Fix Committed => Fix Released

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Stéphane Graber]

** Changed in: screen (Ubuntu)
 Assignee: Christian Brauner (cbrauner) => Stéphane Graber (stgraber)

** Changed in: screen (Ubuntu)
   Status: Triaged => Fix Committed

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Stéphane Graber]

** Changed in: screen (Ubuntu)
   Status: Fix Committed => Triaged

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Christian Brauner]

Fix for screen merged upstream:
https://lists.gnu.org/archive/html/screen-devel/2017-03/msg00014.html

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Christian Brauner]

** Changed in: screen (Ubuntu)
   Status: In Progress => Fix Committed

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Christian Brauner]

Upstream screen patch:
https://lists.gnu.org/archive/html/screen-devel/2017-03/msg00013.html

** Changed in: screen (Ubuntu)
   Status: Triaged => In Progress

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Adam Conrad]

** Changed in: glibc (Ubuntu)
   Status: Triaged => Fix Committed

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Stéphane Graber]

Adam will take care of doing an upload for Ubuntu 17.04 with
5e9a4f378c8607c2ae1aa465436af4321db0e23 included.

** Changed in: glibc (Ubuntu)
 Assignee: (unassigned) => Adam Conrad (adconrad)

** Also affects: screen (Ubuntu)
   Importance: Undecided
   Status: New

** Also affects: tmux (Ubuntu)
   Importance: Undecided
   Status: New

** Changed in: glibc (Ubuntu)
   Status: New => Triaged

** Changed in: screen (Ubuntu)
   Status: New => Triaged

** Changed in: tmux (Ubuntu)
   Status: New => Triaged

** Changed in: screen (Ubuntu)
   Importance: Undecided => High

** Changed in: tmux (Ubuntu)
   Importance: Undecided => High

** Changed in: screen (Ubuntu)
 Assignee: (unassigned) => Christian Brauner (cbrauner)

** Changed in: tmux (Ubuntu)
 Assignee: (unassigned) => Christian Brauner (cbrauner)

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Stéphane Graber]

And my team will take care of distro patching screen and tmux to work
with this.

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Stéphane Graber]

After discussing this on IRC with Adam, Ubuntu will only include the
upstreamed patch and we'll instead resort on patching all affected
downstream pieces of software to deal with the unfortunate new glibc
behavior.

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Ubuntu Foundations Team Bug Bot]

** Tags added: patch

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Stéphane Graber]

stgraber@dakara:~$ lxc exec zesty bash
root@zesty:~# tmux
lost server
root@zesty:~# tty
not a tty
root@zesty:~# echo $?
0
root@zesty:~# dpkg -i *.deb
(Reading database ... 26464 files and directories currently installed.)
Preparing to unpack libc-bin_2.24-7ubuntu3_amd64.deb ...
Unpacking libc-bin (2.24-7ubuntu3) over (2.24-7ubuntu2) ...
Preparing to unpack libc6_2.24-7ubuntu3_amd64.deb ...
Unpacking libc6:amd64 (2.24-7ubuntu3) over (2.24-7ubuntu2) ...
Setting up libc6:amd64 (2.24-7ubuntu3) ...
Setting up libc-bin (2.24-7ubuntu3) ...
Processing triggers for man-db (2.7.6.1-1) ...
root@zesty:~# tty
/proc/self/fd/0
root@zesty:~# echo $?
0
root@zesty:~# tmux
[exited]
root@zesty:~#

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Stéphane Graber]

** Attachment added: "debdiff"
   
https://bugs.launchpad.net/ubuntu/+source/glibc/+bug/1669578/+attachment/4830204/+files/debdiff

** Changed in: glibc (Ubuntu)
   Importance: Undecided => High

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Stéphane Graber]

For screen, we'll need to fix their own checking logic a bit but we'll
work on that patch and send it upstream (and have it also deal with just
getting ENODEV while we're at it).

With the fixed glibc screen reports "Bad tty '/proc/self/fd/0'" because
of it trying to readlink the path it's receiving from ttyname(), that's
an unneeded step and in fact breaks on Linux when dealing with cross-
namespace pts devices.

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Stéphane Graber]

I'm building a patched glibc now with the two patches we'd like included in 
Ubuntu.
Once that's built and tested, I'll attach the debdiff.

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[Bug 1669578] Re: Get ttyname() to work properly in containers

[Stéphane Graber]

Upstream threads: https://sourceware.org/cgi-
bin/search.cgi?q=ttyname+and+ttyname_r=Search%21=extended=all=10=long=wrd=1=1=2221==no=%2Fml
%2Flibc-alpha%2F%25

We've been getting about a report a week about things failing due to
this bug so we really need it sorted this time (most reports are for
screen/tmux and tools that use them like do-release-upgrade).

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