OpenSSH will now adapt IP QoS to actual sessions and traffic

OpenSSH will now adapt IP QoS to actual sessions and traffic. In a fresh commit, Damien Miller (djm@) introduced a significant change, which enables ssh and sshd to set the IP QoS based on what connections and sessions are active.

The commit message says,

List:       openbsd-cvs
Subject:    CVS: cvs.openbsd.org: src
From:       Damien Miller <djm () cvs ! openbsd ! org>
Date:       2025-08-18 3:43:01

CVSROOT:	/cvs
Module name:	src
Changes by:	djm@cvs.openbsd.org	2025/08/17 21:43:01

Modified files:
	usr.bin/ssh    : sshd-session.c sshd-auth.c ssh.c session.c 
	                 serverloop.c packet.h packet.c mux.c misc.c 
	                 clientloop.c channels.h channels.c 

Log message:
Make ssh(1) and sshd(8) set IP QoS (aka IP_TOS, IPV6_TCLASS)
continually at runtime based on what sessions/channels are open.

Previously, ssh(1) and sshd(8) would pick a QoS value when they
were started and use it for the whole connection. This could
produce suboptimal choices for the QoS value, e.g. for multiplexed
sessions that started interactive but picked up a sftp client,
or sessions that moved large amounts of data via port forwarding.

Now the QoS value will change to the non-interactive IPQoS whenever
a "non-interactive" channel is open; basically any channel that lacks
a tty other than agent forwarding.

This is important now that the default interactive IPQoS is EF
(Expedited Forwarding), as many networks are configured to allow
only relatively small amounts of traffic of this class and they will
aggressively deprioritise the entire connection if this is exceeded.

NB. because ssh(1) and sshd(8) now change IP_TOS/IPV6_TCLASS
continually via setsockopt(), this commit requires a recent pledge(2)
change that landed recently in the OpenBSD kernel. Please ensure
you have updated to a kernel from within the last two weeks before
updating OpenSSH.

with job@ deraadt@

Note the last part -- once again, the easiest way to test this change will be to upgrade to a snapshot that has this code integrated.

Also new: ssh(1) and sshd(8) now dump active channel/session information on receiving SIGINFO.