[libvirt] [PATCH] rng: restrict passthrough names to known-good files

[Laine Stump]

On 03/04/2013 06:31 PM, Anthony Liguori wrote:
> Eric Blake <eblake at redhat.com> writes:
>
>> There is some controversy[1] on the qemu list on whether qemu should
>> have ever allowed arbitrary file name passthrough, or whether it
>> should be restricted to JUST /dev/random and /dev/hwrng.  It is
>> always easier to add support for additional filenames than it is
>> to remove support for something once released, so this patch
>> restricts libvirt 1.0.3 (where the virtio-random backend was first
>> supported) to just the two uncontroversial names, letting us defer
>> to a later date any decision on whether supporting arbitrary files
>> makes sense. Additionally, since qemu 1.4 does NOT support
>> /dev/fdset/nnn fd passthrough for the backend, limiting to just
>> two known names means that we don't get tempted to try fd
>> passthrough where it won't work.
> Acked-by: Anthony Liguori <aliguori at us.ibm.com>
>
> Regards,
>
> Anthony Liguori
>
>> [1]https://lists.gnu.org/archive/html/qemu-devel/2013-03/threads.html#00023
>>
>> * src/conf/domain_conf.c (virDomainRNGDefParseXML): Only allow
>> /dev/random and /dev/hwrng.
>> * docs/schemas/domaincommon.rng: Flag invalid files.
>> * docs/formatdomain.html.in (elementsRng): Document this.
>> * tests/qemuxml2argvdata/qemuxml2argv-virtio-rng-random.args:
>> Update test to match.
>> * tests/qemuxml2argvdata/qemuxml2argv-virtio-rng-random.xml:
>> Likewise.
>> ---
>>
>> This needs to be acked before libvirt 1.0.3; otherwise we are
>> stuck supporting arbitrary name passthrough.
>>
>>  docs/formatdomain.html.in                                  | 3 ++-
>>  docs/schemas/domaincommon.rng                              | 5 ++++-
>>  src/conf/domain_conf.c                                     | 7 +++++++
>>  tests/qemuxml2argvdata/qemuxml2argv-virtio-rng-random.args | 2 +-
>>  tests/qemuxml2argvdata/qemuxml2argv-virtio-rng-random.xml  | 2 +-
>>  5 files changed, 15 insertions(+), 4 deletions(-)
>>
>> diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in
>> index 1835b39..4cafc92 100644
>> --- a/docs/formatdomain.html.in
>> +++ b/docs/formatdomain.html.in
>> @@ -4310,7 +4310,8 @@ qemu-kvm -net nic,model=? /dev/null
>>            <code>model</code> attribute. Supported source models are:
>>          </p>
>>          <ul>
>> -          <li>'random' — /dev/random (default) or similar device as source</li>
>> +          <li>'random' — /dev/random (default) or /dev/hwrng
>> +            device as source (for now, no other sources are permitted)</li>
>>            <li>'egd' — a EGD protocol backend</li>
>>          </ul>
>>        </dd>
>> diff --git a/docs/schemas/domaincommon.rng b/docs/schemas/domaincommon.rng
>> index e7231cc..4b60885 100644
>> --- a/docs/schemas/domaincommon.rng
>> +++ b/docs/schemas/domaincommon.rng
>> @@ -3511,7 +3511,10 @@
>>            <attribute name="model">
>>              <value>random</value>
>>            </attribute>
>> -          <ref name="filePath"/>
>> +          <choice>
>> +            <value>/dev/random</value>
>> +            <value>/dev/hwrng</value>
>> +          </choice>
>>          </group>
>>          <group>
>>            <attribute name="model">
>> diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
>> index 995cf0c..9c96cf1 100644
>> --- a/src/conf/domain_conf.c
>> +++ b/src/conf/domain_conf.c
>> @@ -7423,6 +7423,13 @@ virDomainRNGDefParseXML(const xmlNodePtr node,
>>      switch ((enum virDomainRNGBackend) def->backend) {
>>      case VIR_DOMAIN_RNG_BACKEND_RANDOM:
>>          def->source.file = virXPathString("string(./backend)", ctxt);
>> +        if (STRNEQ(def->source.file, "/dev/random") &&
>> +            STRNEQ(def->source.file, "/dev/hwrng")) {
>> +            virReportError(VIR_ERR_XML_ERROR,
>> +                           _("file '%s' is not a supported random source"),
>> +                           def->source.file);
>> +            goto error;
>> +        }
>>          break;
>>
>>      case VIR_DOMAIN_RNG_BACKEND_EGD:
>> diff --git a/tests/qemuxml2argvdata/qemuxml2argv-virtio-rng-random.args b/tests/qemuxml2argvdata/qemuxml2argv-virtio-rng-random.args
>> index ad27132..7ab9dbc 100644
>> --- a/tests/qemuxml2argvdata/qemuxml2argv-virtio-rng-random.args
>> +++ b/tests/qemuxml2argvdata/qemuxml2argv-virtio-rng-random.args
>> @@ -2,5 +2,5 @@ LC_ALL=C PATH=/bin HOME=/home/test USER=test LOGNAME=test /usr/bin/qemu \
>>  -S -M pc -m 214 -smp 1 -nographic -nodefaults \
>>  -monitor unix:/tmp/test-monitor,server,nowait -no-acpi -boot c -usb \
>>  -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x3 \
>> --object 'rng-random,id=rng0,filename=/test/ph<ile' \
>> +-object rng-random,id=rng0,filename=/dev/hwrng \
>>  -device virtio-rng-pci,rng=rng0,bus=pci.0,addr=0x4
>> diff --git a/tests/qemuxml2argvdata/qemuxml2argv-virtio-rng-random.xml b/tests/qemuxml2argvdata/qemuxml2argv-virtio-rng-random.xml
>> index 0658f4b..1e2c4be 100644
>> --- a/tests/qemuxml2argvdata/qemuxml2argv-virtio-rng-random.xml
>> +++ b/tests/qemuxml2argvdata/qemuxml2argv-virtio-rng-random.xml
>> @@ -17,7 +17,7 @@
>>      <controller type='usb' index='0'/>
>>      <memballoon model='virtio'/>
>>      <rng model='virtio'>
>> -      <backend model='random'>/test/ph<ile</backend>
>> +      <backend model='random'>/dev/hwrng</backend>
>>      </rng>
>>    </devices>
>>  </domain>
>> -- 
>> 1.8.1.4

ACK.