On Thu, Jun 25, 2026 at 06:56:05PM +0200, Mauro Matteo Cascella wrote: > On Mon, Jun 22, 2026 at 6:30 PM Daniel P. Berrangé <[email protected]> > wrote: > > > > On Mon, Jun 22, 2026 at 06:11:44PM +0200, Laurent Vivier wrote: > > > A malicious guest can craft virtqueue descriptors with arbitrary lengths. > > > control_out() calls iov_size() on the guest-supplied scatter-gather list > > > and passes the result directly to g_malloc(), allowing a guest to force > > > QEMU to attempt multi-gigabyte allocations and crash the host process. > > > > > > Fix this by copying at most sizeof(struct virtio_console_control) into a > > > stack-local variable instead of allocating a buffer sized by the guest. > > > handle_control_message() only accesses the fixed-size id, event, and > > > value fields, so no data beyond the struct was ever needed. > > > > Does anyone have thoughts on whether we should treat guest initiated > > unbounded allocs as a security issue ? > > > > IIUC, this flaw would require root in the guest OS in order to craft > > the malicious virtqueue descriptors. > > > > A self-initiated crash triggered by root would not historically > > be enough justification for CVE. We would require it to be triggered > > by unprivileged user. > > > > Nested virt with device assignment could change that equation though > > as the L2 guest could be considered an unpriv user from the L1 POV. > > > > Also in theory the large alloc might be large enough to consume all > > host RAM but not large enough to trigger OOM kill of QEMU. This might > > impact operation of other co-located VMs on the same host. > > > > Anyone think this is bad enough to justify a CVE ? Or should we treat > > these OOM scenarios maerely as "hardening" bugs, where they require > > 'root' in the L1 guest ? > > I'd lean toward classifying these as hardening bugs. I don't see the > point in assigning Low CVEs to these kinds of issues nowadays. Under > current vulnerability management standards, they would definitely be > pushed down the priority list and likely skipped or deferred.
Ok, so lets apply as a general rule that all OOM bugs which require privileged access in the guest are not assigned CVEs. An unprivileged guest exploit would be more significant so still potentially in scope. With regards, Daniel -- |: https://berrange.com ~~ https://hachyderm.io/@berrange :| |: https://libvirt.org ~~ https://entangle-photo.org :| |: https://pixelfed.art/berrange ~~ https://fstop138.berrange.com :|
