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



On 03/04/13 23:49, Eric Blake wrote:
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.

Okay, this is fair enough for now.


  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;

This is yet another part of the stuff that will need to be moved out of the parser when I finish the XML parsing callbacks.

Peter


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