CVE-2026-89777

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 vfio_pci_config_rw_single (drivers/vfio/pci/vfio_pci_config.c:1961)

Read of size 8 at addr ffff88800fcc88d0 by task exploit/143

Call Trace:

...

kasan_report (mm/kasan/report.c:595)

vfio_pci_config_rw_single (drivers/vfio/pci/vfio_pci_config.c:1961)

vfio_pci_config_rw (drivers/vfio/pci/vfio_pci_config.c:1986)

vfio_pci_rw (drivers/vfio/pci/vfio_pci_core.c:1599)

vfs_read (fs/read_write.c:572)

__x64_sys_pread64 (fs/read_write.c:764)

do_syscall_64 (arch/x86/entry/syscall_64.c:94)

...

Followed on device close by a double free of the same object:

Oops: general protection fault, probably for non-canonical address

0x1f63e0e8000008: 0000 [#1] SMP KASAN NOPTI

RIP: 0010:kfree (mm/slub.c:6711)

Call Trace:

vfio_config_free (drivers/vfio/pci/vfio_pci_config.c:1861)

vfio_pci_core_disable (drivers/vfio/pci/vfio_pci_core.c:685)

vfio_pci_core_close_device (drivers/vfio/pci/vfio_pci_core.c:777)

vfio_df_close (drivers/vfio/vfio_main.c:602)

vfio_device_fops_release (drivers/vfio/vfio_main.c:648)

__fput (fs/file_table.c:512)

__x64_sys_close (fs/open.c:1496)

do_syscall_64 (arch/x86/entry/syscall_64.c:94)

...

Kernel panic - not syncing: Fatal exception