Re: [PATCH] rpc: Pass OPENSSL_CONF through to ssh invocations

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On 7/25/22 15:38, Laszlo Ersek wrote:
> On 07/25/22 15:09, Richard W.M. Jones wrote:
>> It's no longer possible for libvirt to connect over the ssh transport
>> from RHEL 9 to RHEL 5.  This is because SHA1 signatures have been
>> effectively banned in RHEL 9 at the openssl level.  They are required
>> to check the RHEL 5 host key.  Note this is a separate issue from
>> openssh requiring additional configuration in order to connect to
>> older servers.
>>
>> Connecting from a RHEL 9 client to RHEL 5 server:
>>
>> $ cat ~/.ssh/config
>> Host 192.168.0.91
>>   KexAlgorithms            +diffie-hellman-group14-sha1
>>   MACs                     +hmac-sha1
>>   HostKeyAlgorithms        +ssh-rsa
>>   PubkeyAcceptedKeyTypes   +ssh-rsa
>>   PubkeyAcceptedAlgorithms +ssh-rsa
>>
>> $ virsh -c 'qemu+ssh://root@192.168.0.91/system' list
>> error: failed to connect to the hypervisor
>> error: Cannot recv data: ssh_dispatch_run_fatal: Connection to 192.168.0.91 port 22: error in libcrypto: Connection reset by peer
>>
>> "error in libcrypto: Connection reset by peer" is the characteristic
>> error of openssl having been modified to disable SHA1 by default.
>> (You will not see this on non-RHEL-derived distros.)
>>
>> You could enable the legacy crypto policy which downgrades security on
>> the entire host, but a more fine-grained way to do this is to create
>> an alternate openssl configuration file that enables the "forbidden"
>> signatures.  However this requires passing the OPENSSL_CONF
>> environment variable through to ssh to specify the alternate
>> configuration.  Libvirt filters out this environment variable, but
>> this commit allows it through.  With this commit:
>>
>> $ cat /var/tmp/openssl.cnf
>> .include /etc/ssl/openssl.cnf
>> [openssl_init]
>> alg_section = evp_properties
>> [evp_properties]
>> rh-allow-sha1-signatures = yes
>>
>> $ OPENSSL_CONF=/var/tmp/openssl.cnf ./run virsh -c 'qemu+ssh://root@192.168.0.91/system' list
>> root@192.168.0.91's password:
>>  Id   Name   State
>> --------------------
>>
>> Essentially my argument here is that OPENSSL_CONF is sufficiently
>> similar in nature to KRB5CCNAME, SSH* and XAUTHORITY that we should
>> permit it to be passed through.
>>
>> Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2062360
>> Signed-off-by: Richard W.M. Jones <rjones@xxxxxxxxxx>
>> ---
>>  src/rpc/virnetsocket.c | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/src/rpc/virnetsocket.c b/src/rpc/virnetsocket.c
>> index 32f506d2d4..8280bda007 100644
>> --- a/src/rpc/virnetsocket.c
>> +++ b/src/rpc/virnetsocket.c
>> @@ -855,6 +855,7 @@ int virNetSocketNewConnectSSH(const char *nodename,
>>      virCommandAddEnvPass(cmd, "KRB5CCNAME");
>>      virCommandAddEnvPass(cmd, "SSH_AUTH_SOCK");
>>      virCommandAddEnvPass(cmd, "SSH_ASKPASS");
>> +    virCommandAddEnvPass(cmd, "OPENSSL_CONF");
>>      virCommandAddEnvPass(cmd, "DISPLAY");
>>      virCommandAddEnvPass(cmd, "XAUTHORITY");
>>      virCommandClearCaps(cmd);
>>
> 
> Acked-by: Laszlo Ersek <lersek@xxxxxxxxxx>
> 

Reviewed-by: Michal Privoznik <mprivozn@xxxxxxxxxx>

and merged.

Michal




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