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Bug#1117574: marked as done (openssh-client: output pauses in interactive session over ControlMaster)

Your message dated Thu, 09 Oct 2025 00:20:07 +0000
with message-id <E1v6eO7-00E0nF-0p@fasolo.debian.org>
and subject line Bug#1117574: fixed in openssh 1:10.1p1-2
has caused the Debian Bug report #1117574,
regarding openssh-client: output pauses in interactive session over ControlMaster
to be marked as done.

This means that you claim that the problem has been dealt with.
If this is not the case it is now your responsibility to reopen the
Bug report if necessary, and/or fix the problem forthwith.

(NB: If you are a system administrator and have no idea what this
message is talking about, this may indicate a serious mail system
misconfiguration somewhere. Please contact owner@bugs.debian.org
immediately.)


-- 
1117574: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1117574
Debian Bug Tracking System
Contact owner@bugs.debian.org with problems
--- Begin Message --- 
Package: openssh-client
Version: 1:10.1p1-1
Severity: normal

After upgrading to 10.1p1-1, interactive sessions are very slow and
halting while producing output from the server, as if the client is
missing some poll()/select() triggers. It's a bit hard to show the
timing in an email, but if I ssh to a local machine that is running
trixie's 10.0p1-7, like this:

  $ ssh -o ControlMaster=yes segfault.intra.peff.net

then no output is produced immediately. If I start typing (say, "echo
foo") then output does start appearing, but always behind, as if ssh is
not correctly calling read() until my local typing kicks it into a
polling loop.

If I run the command above under "strace -tt", it sits (with no output)
on this call:

  963687 01:34:16.851998 read(6 <unfinished ...>

And if I then type "echo foo", I finally get some output, with strace
showing:

  963687 01:35:08.915571 <... read resumed>, "e", 16384) = 1
  963687 01:35:08.915862 write(3, "9=\227\2137\346}\236\222A.82\253\253A\222\211Y\323>\251\243\362\t\314 \364\206B\37\223"..., 640) = 640
  963687 01:35:08.916391 rt_sigprocmask(SIG_BLOCK, [HUP INT QUIT TERM], [], 8) = 0
  963687 01:35:08.916844 ppoll([{fd=3, events=POLLIN}, {fd=3, events=0}, {fd=4, events=POLLIN}, {fd=5, events=POLLIN}], 4, NULL, [], 8) = 1 ([{fd=3, revents=POLLIN}])
  963687 01:35:09.925713 rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
  963687 01:35:09.926143 read(6, "cho ", 16384) = 4
  963687 01:35:09.926461 read(3, "X\343E\253\376\361\24\351\342\217\236J\266\3\322d\taw\246\34A:\212/#\353\227\v\301B\361"..., 262144) = 300
  963687 01:35:09.926758 getrandom("\x53\x8c\x43\xe3\x6c\x36\x51\xe1\xb9\x80\xe9\x6b\xd3\x66\x19\xdd\x14\x91\x6f\x8f\xf3\xe7\xaf\x8f\x2f\x72\x5f\x11\xfc\x82\x79\xf6", 32, 0) = 32
  963687 01:35:09.926946 rt_sigprocmask(SIG_BLOCK, [HUP INT QUIT TERM], [], 8) = 0
  963687 01:35:09.927062 ppoll([{fd=3, events=POLLIN}, {fd=3, events=POLLOUT}, {fd=4, events=POLLIN}, {fd=5, events=POLLIN}, {fd=6, events=POLLIN}, {fd=7, events=POLLOUT}], 6, {tv_sec=0, tv_nsec=19346284}, [], 8) = 2 ([{fd=3, revents=POLLOUT}, {fd=7, revents=POLLOUT}], left {tv_sec=0, tv_nsec=19335352})
  963687 01:35:09.927200 rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
  963687 01:35:09.927302 read(6, "f", 16384) = 1
  963687 01:35:10.099933 write(7, "Last login: Wed Oct  8 01:34:00 "..., 117) = 117

So you can see it sat for half a minute before I typed anything, and
then after I did, it eventually polled the other side and got the "Last
login" line from the server. It's curious that it's waiting in read()
and not poll(). If we go back a few lines in the strace output, I see:

  963687 01:34:16.851910 ppoll([{fd=3, events=POLLIN}, {fd=3, events=POLLOUT}, {fd=4, events=POLLIN}, {fd=5, events=POLLIN|POLLOUT}], 4, NULL, [], 8) = 2 ([{fd=3, revents=POLLOUT}, {fd=5, revents=POLLOUT}])
  963687 01:34:16.851941 rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
  963687 01:34:16.851967 write(5, "\0\0\0\f\200\0\0\6\0\0\0\1\0\0\0\2", 16) = 16
  963687 01:34:16.851998 read(6 <unfinished ...>

So we did poll(), and it told us there were interesting things to see,
but descriptor 6 was not one of them. So presumably the bug is there.

The problem reproduces against multiple trixie machines, as well as
against public ssh servers like github.com. Downgrading back to 10.0p1-8
makes it go away. Running without "-o ControlMaster=no" likewise runs
fine and quickly. And running a non-interactive session, even with a
ControlMaster (e.g., "ssh $host echo foo") likewise is fine.

-- System Information:
Debian Release: forky/sid
  APT prefers unstable
  APT policy: (500, 'unstable'), (500, 'testing'), (1, 'experimental')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 6.16.8+deb14-amd64 (SMP w/16 CPU threads; PREEMPT)
Kernel taint flags: TAINT_PROPRIETARY_MODULE, TAINT_OOT_MODULE, TAINT_UNSIGNED_MODULE
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages openssh-client depends on:
ii  adduser              3.153
ii  init-system-helpers  1.69
ii  libc6                2.41-12
ii  libedit2             3.1-20250104-1
ii  libfido2-1           1.16.0-2
ii  libgssapi-krb5-2     1.21.3-5
ii  libselinux1          3.8.1-1
ii  libssl3t64           3.5.4-1
ii  passwd               1:4.18.0-1
ii  zlib1g               1:1.3.dfsg+really1.3.1-1+b1

Versions of packages openssh-client recommends:
ii  xauth  1:1.1.2-1.1

Versions of packages openssh-client suggests:
pn  keychain      <none>
pn  libpam-ssh    <none>
pn  monkeysphere  <none>
ii  ssh-askpass   1:1.2.4.1-16+b1

-- no debconf information

--- End Message ---
--- Begin Message --- 
Source: openssh
Source-Version: 1:10.1p1-2
Done: Colin Watson <cjwatson@debian.org>

We believe that the bug you reported is fixed in the latest version of
openssh, which is due to be installed in the Debian FTP archive.

A summary of the changes between this version and the previous one is
attached.

Thank you for reporting the bug, which will now be closed.  If you
have further comments please address them to 1117574@bugs.debian.org,
and the maintainer will reopen the bug report if appropriate.

Debian distribution maintenance software
pp.
Colin Watson <cjwatson@debian.org> (supplier of updated openssh package)

(This message was generated automatically at their request; if you
believe that there is a problem with it please contact the archive
administrators by mailing ftpmaster@ftp-master.debian.org)


-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA512

Format: 1.8
Date: Thu, 09 Oct 2025 00:54:25 +0100
Source: openssh
Architecture: source
Version: 1:10.1p1-2
Distribution: unstable
Urgency: medium
Maintainer: Debian OpenSSH Maintainers <debian-ssh@lists.debian.org>
Changed-By: Colin Watson <cjwatson@debian.org>
Closes: 1117574 1117594
Changes:
 openssh (1:10.1p1-2) unstable; urgency=medium
 .
   * Don't reuse c->isatty for signalling that the remote channel has a tty
     attached (closes: #1117574, #1117594).
   * Link ssh-keygen directly against ssh-pkcs11.c.
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Files:
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Git-Tag-Info: tag=33c021362ac506111e178e031e13add40122ca97 fp=ac0a4ff12611b6fccf01c111393587d97d86500b
Git-Tag-Tagger: Colin Watson <cjwatson@debian.org>

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--- End Message ---
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