CVE-2026-89777

Summary

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

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/eb84cd81040e58dd05ac190f561f2115e3367249
• https://git.kernel.org/stable/c/f0eea8f9013676b42289ec35941e848b8a543e19
• https://git.kernel.org/stable/c/d665a1688af7f8fefd7c0eb04f2a37122ce007f4
• https://git.kernel.org/stable/c/25cdd2a492d868cff1e519a60fe282909c52d385
• https://git.kernel.org/stable/c/812f1db7f0755a19ef16ecdc5cec51bcabc5eda5
• https://git.kernel.org/stable/c/533d0c5feef85ee6404b9f41d5564fac6971a008
• https://git.kernel.org/stable/c/fda8fb7e8179561693a786a7af593f6b944a21c1
• https://git.kernel.org/stable/c/dc77acfeb979dded39b247b60fef0399536bfa77

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