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

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. [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/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;