CVE-2026-89777 — vfio/pci: clear vdev->msi_perm after freeing it on init failure

Affected: Linux

In the Linux kernel, the following vulnerability has been resolved:

vfio/pci: clear vdev->msi_perm after freeing it on init failure

vfio_msi_cap_len() lazily allocates the per-device MSI permission table:

vdev->msi_perm = kmalloc_obj(struct perm_bits, GFP_KERNEL_ACCOUNT); if (!vdev->msi_perm) return -ENOMEM;

ret = init_pci_cap_msi_perm(vdev->msi_perm, len, flags); if (ret) { kfree(vdev->msi_perm); return ret; /* vdev->msi_perm left dangling */ }

When init_pci_cap_msi_perm() -> alloc_perm_bits() fails with -ENOMEM, the error path frees vdev->msi_perm but leaves the freed pointer stored in it. vdev->msi_perm is not re-zeroed later because struct vfio_pci_core_device is per-device and persists across open/close cycles, and the vfio_config_init() error path returns without calling vfio_config_free(). So the dangling pointer outlives the failed open.

That leads to two use-after-frees on the same device:

1. Reuse. The next vfio_config_init() sees the stale pointer at "if (vdev->msi_perm) return len;" and reuses the freed object. MSI config accesses in vfio_pci_config_rw_single() then dereference and call the freed perm->readfn / perm->writefn function pointers.

2. Double free. A later vfio_config_free() runs free_perm_bits() and kfree() on the already-freed object.

Fix it by NULLing vdev->msi_perm after the kfree(), matching the NULL-after-free discipline already used in free_perm_bits() and vfio_config_free().

BUG: KASAN: slab-use-after-free in…

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CVE-2026-89777 — vfio/pci: clear vdev->msi_perm after freeing it on init failure