Various Debian-specific configuration changes

ssh: Enable ForwardX11Trusted, returning to earlier semantics which cause
fewer problems with existing setups (http://bugs.debian.org/237021).

ssh: Set 'SendEnv LANG LC_*' by default (http://bugs.debian.org/264024).

ssh: Enable HashKnownHosts by default to try to limit the spread of ssh
worms.

ssh: Enable GSSAPIAuthentication by default.

ssh: Include /etc/ssh/ssh_config.d/*.conf.

sshd: Enable PAM, disable ChallengeResponseAuthentication, and disable
PrintMotd.

sshd: Enable X11Forwarding.

sshd: Set 'AcceptEnv LANG LC_*' by default.

sshd: Change sftp subsystem path to /usr/lib/openssh/sftp-server.

sshd: Include /etc/ssh/sshd_config.d/*.conf.

Document all of this.

Author: Russ Allbery <rra@debian.org>
Forwarded: not-needed
Last-Update: 2020-10-18

Patch-Name: debian-config.patch

6 files changed, 98 insertions, 9 deletions

diff --git a/readconf.c b/readconf.c
index f4f273c96..e676b6be6 100644
--- a/readconf.c
+++ b/readconf.c
@@ -2153,7 +2153,7 @@ fill_default_options(Options * options)
         if (options->forward_x11 == -1)
                 options->forward_x11 = 0;
         if (options->forward_x11_trusted == -1)
-                options->forward_x11_trusted = 0;
+                options->forward_x11_trusted = 1;
         if (options->forward_x11_timeout == -1)
                 options->forward_x11_timeout = 1200;
         /*
diff --git a/ssh.1 b/ssh.1
index 76ddd89b5..ad48fc8c8 100644
--- a/ssh.1
+++ b/ssh.1
@@ -812,6 +812,16 @@ directive in
 .Xr ssh_config 5
 for more information.
 .Pp
+(Debian-specific: X11 forwarding is not subjected to X11 SECURITY extension
+restrictions by default, because too many programs currently crash in this
+mode.
+Set the
+.Cm ForwardX11Trusted
+option to
+.Dq no
+to restore the upstream behaviour.
+This may change in future depending on client-side improvements.)
+.Pp
 .It Fl x
 Disables X11 forwarding.
 .Pp
@@ -820,6 +830,20 @@ Enables trusted X11 forwarding.
 Trusted X11 forwardings are not subjected to the X11 SECURITY extension
 controls.
 .Pp
+(Debian-specific: In the default configuration, this option is equivalent to
+.Fl X ,
+since
+.Cm ForwardX11Trusted
+defaults to
+.Dq yes
+as described above.
+Set the
+.Cm ForwardX11Trusted
+option to
+.Dq no
+to restore the upstream behaviour.
+This may change in future depending on client-side improvements.)
+.Pp
 .It Fl y
 Send log information using the
 .Xr syslog 3
diff --git a/ssh_config b/ssh_config
index 52aae8692..09a17cf18 100644
--- a/ssh_config
+++ b/ssh_config
@@ -17,9 +17,12 @@
 # list of available options, their meanings and defaults, please see the
 # ssh_config(5) man page.
 
-# Host *
+Include /etc/ssh/ssh_config.d/*.conf
+
+Host *
 #   ForwardAgent no
 #   ForwardX11 no
+#   ForwardX11Trusted yes
 #   PasswordAuthentication yes
 #   HostbasedAuthentication no
 #   GSSAPIAuthentication no
@@ -46,3 +49,6 @@
 #   ProxyCommand ssh -q -W %h:%p gateway.example.com
 #   RekeyLimit 1G 1h
 #   UserKnownHostsFile ~/.ssh/known_hosts.d/%k
+    SendEnv LANG LC_*
+    HashKnownHosts yes
+    GSSAPIAuthentication yes
diff --git a/ssh_config.5 b/ssh_config.5
index 96ca7a5df..6d6c59521 100644
--- a/ssh_config.5
+++ b/ssh_config.5
@@ -71,6 +71,29 @@ Since the first obtained value for each parameter is used, more
 host-specific declarations should be given near the beginning of the
 file, and general defaults at the end.
 .Pp
+Note that the Debian
+.Ic openssh-client
+package sets several options as standard in
+.Pa /etc/ssh/ssh_config
+which are not the default in
+.Xr ssh 1 :
+.Pp
+.Bl -bullet -offset indent -compact
+.It
+.Cm Include /etc/ssh/ssh_config.d/*.conf
+.It
+.Cm SendEnv No LANG LC_*
+.It
+.Cm HashKnownHosts No yes
+.It
+.Cm GSSAPIAuthentication No yes
+.El
+.Pp
+.Pa /etc/ssh/ssh_config.d/*.conf
+files are included at the start of the system-wide configuration file, so
+options set there will override those in
+.Pa /etc/ssh/ssh_config.
+.Pp
 The file contains keyword-argument pairs, one per line.
 Lines starting with
 .Ql #
@@ -742,11 +765,12 @@ elapsed.
 .It Cm ForwardX11Trusted
 If this option is set to
 .Cm yes ,
+(the Debian-specific default),
 remote X11 clients will have full access to the original X11 display.
 .Pp
 If this option is set to
 .Cm no
-(the default),
+(the upstream default),
 remote X11 clients will be considered untrusted and prevented
 from stealing or tampering with data belonging to trusted X11
 clients.
diff --git a/sshd_config b/sshd_config
index 2c48105f8..459c1b230 100644
--- a/sshd_config
+++ b/sshd_config
@@ -10,6 +10,8 @@
 # possible, but leave them commented.  Uncommented options override the
 # default value.
 
+Include /etc/ssh/sshd_config.d/*.conf
+
 #Port 22
 #AddressFamily any
 #ListenAddress 0.0.0.0
@@ -57,8 +59,9 @@ AuthorizedKeysFile	.ssh/authorized_keys
 #PasswordAuthentication yes
 #PermitEmptyPasswords no
 
-# Change to no to disable s/key passwords
-#ChallengeResponseAuthentication yes
+# Change to yes to enable challenge-response passwords (beware issues with
+# some PAM modules and threads)
+ChallengeResponseAuthentication no
 
 # Kerberos options
 #KerberosAuthentication no
@@ -81,16 +84,16 @@ AuthorizedKeysFile	.ssh/authorized_keys
 # If you just want the PAM account and session checks to run without
 # PAM authentication, then enable this but set PasswordAuthentication
 # and ChallengeResponseAuthentication to 'no'.
-#UsePAM no
+UsePAM yes
 
 #AllowAgentForwarding yes
 #AllowTcpForwarding yes
 #GatewayPorts no
-#X11Forwarding no
+X11Forwarding yes
 #X11DisplayOffset 10
 #X11UseLocalhost yes
 #PermitTTY yes
-#PrintMotd yes
+PrintMotd no
 #PrintLastLog yes
 #TCPKeepAlive yes
 #PermitUserEnvironment no
@@ -107,8 +110,11 @@ AuthorizedKeysFile	.ssh/authorized_keys
 # no default banner path
 #Banner none
 
+# Allow client to pass locale environment variables
+AcceptEnv LANG LC_*
+
 # override default of no subsystems
-Subsystem       sftp    /usr/libexec/sftp-server
+Subsystem       sftp    /usr/lib/openssh/sftp-server
 
 # Example of overriding settings on a per-user basis
 #Match User anoncvs
diff --git a/sshd_config.5 b/sshd_config.5
index 32ae46476..472001dd1 100644
--- a/sshd_config.5
+++ b/sshd_config.5
@@ -56,6 +56,35 @@ Arguments may optionally be enclosed in double quotes
 .Pq \&"
 in order to represent arguments containing spaces.
 .Pp
+Note that the Debian
+.Ic openssh-server
+package sets several options as standard in
+.Pa /etc/ssh/sshd_config
+which are not the default in
+.Xr sshd 8 :
+.Pp
+.Bl -bullet -offset indent -compact
+.It
+.Cm Include /etc/ssh/sshd_config.d/*.conf
+.It
+.Cm ChallengeResponseAuthentication No no
+.It
+.Cm X11Forwarding No yes
+.It
+.Cm PrintMotd No no
+.It
+.Cm AcceptEnv No LANG LC_*
+.It
+.Cm Subsystem No sftp /usr/lib/openssh/sftp-server
+.It
+.Cm UsePAM No yes
+.El
+.Pp
+.Pa /etc/ssh/sshd_config.d/*.conf
+files are included at the start of the configuration file, so options set
+there will override those in
+.Pa /etc/ssh/sshd_config.
+.Pp
 The possible
 keywords and their meanings are as follows (note that
 keywords are case-insensitive and arguments are case-sensitive):