On Wed, Sep 11, 2024 at 18:24:07 -0400, Laine Stump wrote:
On 9/11/24 5:02 PM, Jim Fehlig via Devel wrote:
The Xen libxl driver does not support nwfilter. Add a check for nwfilters to the devicesPostParseCallback, returning VIR_ERR_CONFIG_UNSUPPORTED if any are found.
It's generally preferred for drivers to ignore unsupported XML features,
I would instead characterize it as "drivers generally ignore *unrecognized* XML", but it's quite common for a bit of XML that's understood and supported in one context within libvirt to generate an UNSUPPORTED error when attempting to use it in a place where it isn't supported.
but ignoring a user's request to filter VM network traffic can be viewed as a security issue.
Definitely.
Signed-off-by: Jim Fehlig <jfehlig@suse.com> --- src/libxl/libxl_domain.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/src/libxl/libxl_domain.c b/src/libxl/libxl_domain.c index 0f129ec69c..2f6cebb8ae 100644 --- a/src/libxl/libxl_domain.c +++ b/src/libxl/libxl_domain.c @@ -131,6 +131,13 @@ libxlDomainDeviceDefPostParse(virDomainDeviceDef *dev, void *opaque G_GNUC_UNUSED, void *parseOpaque G_GNUC_UNUSED) { + if (dev->type == VIR_DOMAIN_DEVICE_NET && dev->data.net->filter) { + virReportError(VIR_ERR_CONFIG_UNSUPPORTED, + _("filterref is not supported in %1$s"), + virDomainVirtTypeToString(def->virtType)); + return -1; + } +
This more properly should be in a function called libxlValidateDomainDeviceDef(), which would look something like qemuValidateDomainDeviceDef() and be added into libxlDomainDefParserConfig with this initialization:
.deviceValidateCallback = libxlValidateDomainDeviceDef,
(my understanding of the purpose of the two has always been that the PostParse callback is intended for performing post-parse modifications/fixups to the domain def, while the Validate only checks for correctness, without modifying anything. There are multiple cases of having validation in the postparse function, but I think those are the 1) leftovers from before the introduction of the validate callbacks, and 2) the result of misunderstanding and/or sloth (e.g. in cases where you want to validate something, but the driver you're adding this validation to doesn't already have a deviceValidateCallback)
The main difference between the two is that 'postParse' is called on every parse of a XML. That means also for parsing the XMLs of persistently defined domains. If you reject parsing of a XML in a 'postParse' it fails to load the persistent definition so the VM "vanishes", which is something we don't want to do. Thus doing validation in postParse is really valid only when it's a new attribute or configuration that can't exist in "defined" state. In contrast the validate callback is applied in a limited set of XML entrypoints which then don't make the VM to vanish and certain other situations. For that reason the 'Validate' callback/step needs to be re-tried when starting the VM. Other than that, what you've said is correct.