[libvirt] [PATCH] qemu: ensure TLS clients always verify the server certificate

[Daniel P. Berrange]

The default_tls_x509_verify (and related) parameters in qemu.conf
control whether the QEMU TLS servers request & verify certificates
from clients. This works as a simple access control system for
servers by requiring the CA to issue certs to permitted clients.
This use of client certificates is disabled by default, since it
requires extra work to issue client certificates.

Unfortunately the code was using this configuration parameter when
setting up both TLS clients and servers in QEMU. The result was that
TLS clients for character devices and disk devices had verification
turned off, meaning they would ignore errors while validating the
server certificate.

This allows for trivial MITM attacks between client and server,
as any certificate returned by the attacker will be accepted by
the client.

This is assigned CVE-2017-1000256  / LSN-2017-0002

Reviewed-by: Eric Blake <eblake at redhat.com>
Signed-off-by: Daniel P. Berrange <berrange at redhat.com>
---

Pushed as a off-list reviewed security fix.

 src/qemu/qemu_command.c                                                 | 2 +-
 tests/qemuxml2argvdata/qemuxml2argv-serial-tcp-tlsx509-chardev.args     | 2 +-
 .../qemuxml2argv-serial-tcp-tlsx509-secret-chardev.args                 | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index 46f0bdd18c..f68b82d083 100644
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -721,7 +721,7 @@ qemuBuildTLSx509BackendProps(const char *tlspath,
     if (virJSONValueObjectCreate(propsret,
                                  "s:dir", path,
                                  "s:endpoint", (isListen ? "server": "client"),
-                                 "b:verify-peer", verifypeer,
+                                 "b:verify-peer", (isListen ? verifypeer : true),
                                  NULL) < 0)
         goto cleanup;
 
diff --git a/tests/qemuxml2argvdata/qemuxml2argv-serial-tcp-tlsx509-chardev.args b/tests/qemuxml2argvdata/qemuxml2argv-serial-tcp-tlsx509-chardev.args
index 5aff7734e1..ab5f7e27f2 100644
--- a/tests/qemuxml2argvdata/qemuxml2argv-serial-tcp-tlsx509-chardev.args
+++ b/tests/qemuxml2argvdata/qemuxml2argv-serial-tcp-tlsx509-chardev.args
@@ -26,7 +26,7 @@ server,nowait \
 localport=1111 \
 -device isa-serial,chardev=charserial0,id=serial0 \
 -object tls-creds-x509,id=objcharserial1_tls0,dir=/etc/pki/libvirt-chardev,\
-endpoint=client,verify-peer=no \
+endpoint=client,verify-peer=yes \
 -chardev socket,id=charserial1,host=127.0.0.1,port=5555,\
 tls-creds=objcharserial1_tls0 \
 -device isa-serial,chardev=charserial1,id=serial1 \
diff --git a/tests/qemuxml2argvdata/qemuxml2argv-serial-tcp-tlsx509-secret-chardev.args b/tests/qemuxml2argvdata/qemuxml2argv-serial-tcp-tlsx509-secret-chardev.args
index 91f1fe0cde..2567abbfad 100644
--- a/tests/qemuxml2argvdata/qemuxml2argv-serial-tcp-tlsx509-secret-chardev.args
+++ b/tests/qemuxml2argvdata/qemuxml2argv-serial-tcp-tlsx509-secret-chardev.args
@@ -31,7 +31,7 @@ localport=1111 \
 data=9eao5F8qtkGt+seB1HYivWIxbtwUu6MQtg1zpj/oDtUsPr1q8wBYM91uEHCn6j/1,\
 keyid=masterKey0,iv=AAECAwQFBgcICQoLDA0ODw==,format=base64 \
 -object tls-creds-x509,id=objcharserial1_tls0,dir=/etc/pki/libvirt-chardev,\
-endpoint=client,verify-peer=no,passwordid=charserial1-secret0 \
+endpoint=client,verify-peer=yes,passwordid=charserial1-secret0 \
 -chardev socket,id=charserial1,host=127.0.0.1,port=5555,\
 tls-creds=objcharserial1_tls0 \
 -device isa-serial,chardev=charserial1,id=serial1 \
-- 
2.13.5