CVE-2026-31601 in Linux
Zusammenfassung
von VulDB • 21.05.2026
Based on the stack trace and the description provided, this appears to be a kernel bug report (likely from `syzkaller` or similar fuzzing tool) involving a **Use-After-Free** or **Null Pointer Dereference** (indicated by `RAX: ffffffffffffffda` which is `-22` or `-EINVAL` in error codes, but often `0xffffffffffffffda` in raw registers can indicate a corrupted pointer or specific error return being misinterpreted, though more likely here it's an error code from a failed operation).
However, the key insight is in the description: > "This is caused by the fact that some of the `xe_vfio_pci_core_device` members needed for handling reset are only initialized as part of migration init."
And the fix: > "Fix the problem by reorganizing the code to decouple VF init from migration init."
### Analysis
1. **Problem**: The `xe_vfio_pci_core_device` structure has members that are required for reset handling. These members are currently initialized during the **migration init** phase. 2. **Trigger**: A reset operation is attempted (likely via `__x64_sys_write` or similar, possibly through a VFIO ioctl or sysfs interface) **before** migration init has completed. 3. **Result**: Since the required members are not yet initialized, the reset handling code accesses uninitialized or NULL pointers, leading to a crash or error (the `RAX` value suggests an error return, but the stack trace shows a crash path, possibly due to a subsequent invalid memory access after the error).
### Solution Strategy
The fix involves **decoupling** the initialization of VF (Virtual Function) specific data from the migration-specific initialization. This ensures that the data needed for reset is available as soon as the VF is initialized, regardless of whether migration has been initialized.
### Code Change Outline
You would need to modify the `xe_vfio_pci_core_device` initialization logic. Specifically:
1. **Identify the members**: Find which members of `xe_vfio_pci_core_device` are needed for reset handling. 2. **Move initialization**: Move the initialization of these members from the migration init function (e.g., `xe_vfio_migration_init`) to the VF init function (e.g., `xe_vfio_pci_core_init` or similar). 3. **Ensure order**: Make sure that the VF init happens before any reset operations can be triggered.
### Example Patch Structure
```c // Before: Migration init might look like this static int xe_vfio_migration_init(struct xe_vfio_pci_core_device *vfdev) {
// ... other migration-specific init ... // These members were initialized here, but they are needed for reset vfdev->reset_member_1 = kmalloc(...); vfdev->reset_member_2 = kzalloc(...); return 0; }
// After: Move reset-related init to VF init static int xe_vfio_pci_core_init(struct xe_vfio_pci_core_device *vfdev) {
// ... other VF-specific init ... // Initialize members needed for reset here vfdev->reset_member_1 = kmalloc(...); if (!vfdev->reset_member_1) return -ENOMEM; vfdev->reset_member_2 = kzalloc(...); if (!vfdev->reset_member_2) {
kfree(vfdev->reset_member_1); return -ENOMEM; } return 0; }
// Migration init can now assume these are already initialized static int xe_vfio_migration_init(struct xe_vfio_pci_core_device *vfdev) {
// ... other migration-specific init ... // No need to re-initialize reset members return 0; } ```
### Key Points
- **Decoupling**: Ensure that reset-critical data is initialized during VF setup, not migration setup. - **Error Handling**: Properly handle allocation failures in the new location. - **Testing**: Verify that reset operations work correctly even if migration is not initialized.
This change ensures that the `xe_vfio_pci_core_device` is in a valid state for reset handling as soon as the VF is initialized, preventing the crash observed in the stack trace.
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