[Libguestfs] [v2v PATCH] input-xen: cover RHEL9 OpenSSL crypto settings

[Laszlo Ersek]

In commit af4a0454cdd2 ("input-xen: replace "enable LEGACY crypto" advice
with targeted ssh options", 2022-07-11), we documented how the libssh /
openssh crypto settings needed to be relaxed, for connecting to RHEL5
sshd.

It turns out that in RHEL9, the non-LEGACY crypto policies disable SHA1 in
signature algorithms even at the OpenSSL level. Explain how the user can
re-enable that separately, for individual virt-v2v invocations.

The method depends on Rich's libvirt commit 45912ac399ab ("rpc: Pass
OPENSSL_CONF through to ssh invocations", 2022-07-25), which is is going
to be released in upstream libvirt v8.6.0.

Thanks: Dmitry Belyavskiy & Rich Jones
Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2062360
Signed-off-by: Laszlo Ersek <lersek at redhat.com>
---
 docs/virt-v2v-input-xen.pod | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/docs/virt-v2v-input-xen.pod b/docs/virt-v2v-input-xen.pod
index 789853b4d194..4a0544f8d16a 100644
--- a/docs/virt-v2v-input-xen.pod
+++ b/docs/virt-v2v-input-xen.pod
@@ -54,6 +54,26 @@ new one. Virt-v2v uses both C<libssh> and C<ssh> when converting a guest
 from Xen, and on some operating systems, C<libssh> and C<ssh> may not
 both accept the same option variant.)
 
+When connecting to RHEL 5 sshd from RHEL 9, the SHA1 algorithm's use in
+signatures has to be re-enabled at the OpenSSL level, in addition to the
+above SSH configuration.  Create a file called F<$HOME/openssl-sha1.cnf>
+with the following contents:
+
+ .include /etc/ssl/openssl.cnf
+ [openssl_init]
+ alg_section = evp_properties
+ [evp_properties]
+ rh-allow-sha1-signatures = yes
+
+and export the following variable into the environment of the
+C<virt-v2v> process:
+
+ OPENSSL_CONF=$HOME/openssl-sha1.cnf
+
+Note that the C<OPENSSL_CONF> environment variable will only take effect
+if the libvirt client library used by virt-v2v is at least version
+8.6.0.
+
 =head2 Test libvirt connection to remote Xen host
 
 Use the L<virsh(1)> command to list the guests on the remote Xen host:
-- 
2.19.1.3.g30247aa5d201