Linux iommufd: vDEVICE alloc error path leaks the igroup mutex and deadlocks later vDEVICE operations

Impact

iommufd_vdevice_alloc_ioctl() takes idev->igroup->lock, then validates the driver-supplied vdevice_size against the core structure size behind a WARN_ON_ONCE. On failure it jumped past the unlock label, leaving the igroup mutex held permanently - every subsequent vDEVICE operation on that IOMMU group blocks forever. iommufd is the path GPU and NIC passthrough runs through, so a stuck igroup means VMs or containers bound to those devices can no longer be set up or torn down and the node has to be rebooted to clear it. The failing branch is a driver/core size mismatch rather than anything a tenant supplies, so this is a bad-combination bug, not a tenant-reachable one - it needs a vIOMMU driver whose vdevice_size disagrees with the core kernel it is built against.

Who can reach it

Local, from a process holding /dev/iommu that issues the vDEVICE alloc ioctl - in practice the VMM or a passthrough-capable orchestrator, not a tenant workload. Reaching the buggy path additionally requires a vIOMMU driver reporting a mismatched vdevice_size, which the kernel already flags with WARN_ON_ONCE.

What to do

Fixed in the mainline Linux kernel by jumping to the unlock label; take the distro kernel update and reboot the host. A node that has already hit the leak cannot be recovered without a reboot, since the mutex is held by no live path. The record names no fixed release version, only the stable commits.

References

Related entries

• Linux kernel idxd: double free of wq, engine and group structs on setup error and cleanup pathsCVE-2026-80698 · Linux kernel dmaengine idxd (Intel DSA/IAA wq, engine and group device setup)Unscored
• Linux kernel KVM arm64 vGIC: double-deactivate of nested IRQs trips an AmpereOne erratumCVE-2026-80699 · Linux kernel KVM/arm64 vGIC (nested-context IRQ deactivation)Unscored
• Linux kernel MGLRU: stale batch updates after memcg reparenting cause premature OOM killsCVE-2026-80719 · Linux kernel mm MGLRU (per-generation batch accounting across memcg reparenting)Unscored
• Microsoft Hyper-V: vmswitch fails to validate guest OID requestsCVE-2021-28476 · Microsoft Hyper-VCritical
• Incus: instance snapshots bypass restricted.containers.lowlevel, giving command execution on the hostCVE-2026-48751 · Incus (instance snapshots ignore restricted.containers.lowlevel)Critical
• VMware ESXi (OpenSLP): Use-after-free in OpenSLP on port 427 - unauthenticated remote code execution on the hypervisorCVE-2020-3992 · VMware ESXi (OpenSLP)Critical