GSSAPI key exchange support

This patch has been rejected upstream: "None of the OpenSSH developers are
in favour of adding this, and this situation has not changed for several
years.  This is not a slight on Simon's patch, which is of fine quality, but
just that a) we don't trust GSSAPI implementations that much and b) we don't
like adding new KEX since they are pre-auth attack surface.  This one is
particularly scary, since it requires hooks out to typically root-owned
system resources."

However, quite a lot of people rely on this in Debian, and it's better to
have it merged into the main openssh package rather than having separate
-krb5 packages (as we used to have).  It seems to have a generally good
security history.

Author: Simon Wilkinson <simon@sxw.org.uk>
Author: Colin Watson <cjwatson@debian.org>
Author: Jakub Jelen <jjelen@redhat.com>
Origin: other, https://github.com/openssh-gsskex/openssh-gsskex/commits/debian/master
Bug: https://bugzilla.mindrot.org/show_bug.cgi?id=1242
Last-Updated: 2020-06-07

Patch-Name: gssapi.patch

1 files changed, 30 insertions, 0 deletions

diff --git a/sshd_config.5 b/sshd_config.5
index 6fa421cae..eabbe9e73 100644
--- a/sshd_config.5
+++ b/sshd_config.5
@@ -644,6 +644,11 @@ Specifies whether to automatically destroy the user's credentials cache
 on logout.
 The default is
 .Cm yes .
+.It Cm GSSAPIKeyExchange
+Specifies whether key exchange based on GSSAPI is allowed. GSSAPI key exchange
+doesn't rely on ssh keys to verify host identity.
+The default is
+.Cm no .
 .It Cm GSSAPIStrictAcceptorCheck
 Determines whether to be strict about the identity of the GSSAPI acceptor
 a client authenticates against.
@@ -658,6 +663,31 @@ machine's default store.
 This facility is provided to assist with operation on multi homed machines.
 The default is
 .Cm yes .
+.It Cm GSSAPIStoreCredentialsOnRekey
+Controls whether the user's GSSAPI credentials should be updated following a
+successful connection rekeying. This option can be used to accepted renewed
+or updated credentials from a compatible client. The default is
+.Dq no .
+.Pp
+For this to work
+.Cm GSSAPIKeyExchange
+needs to be enabled in the server and also used by the client.
+.It Cm GSSAPIKexAlgorithms
+The list of key exchange algorithms that are accepted by GSSAPI
+key exchange. Possible values are
+.Bd -literal -offset 3n
+gss-gex-sha1-,
+gss-group1-sha1-,
+gss-group14-sha1-,
+gss-group14-sha256-,
+gss-group16-sha512-,
+gss-nistp256-sha256-,
+gss-curve25519-sha256-
+.Ed
+.Pp
+The default is
+.Dq gss-group14-sha256-,gss-group16-sha512-,gss-nistp256-sha256-,gss-curve25519-sha256-,gss-gex-sha1-,gss-group14-sha1- .
+This option only applies to connections using GSSAPI.
 .It Cm HostbasedAcceptedKeyTypes
 Specifies the key types that will be accepted for hostbased authentication
 as a list of comma-separated patterns.