In the Linux kernel, a security vulnerability has been discovered and resolved in the vfio/pci subsystem, specifically in the handling of INTx interrupts. This vulnerability could potentially allow an attacker to cause a denial of service (DoS) or impact system stability. In this post, we will delve into the details of the vulnerability, its potential impact, and the solution that has been implemented to resolve it.
Vulnerability Background
The Linux kernel's vfio/pci subsystem allows for userspace applications to directly access and control PCI devices such as network interfaces and other hardware devices. This functionality is important for virtualization and other userspace applications that require more direct control over hardware components.
The issue stems from the fact that the eventfd for INTx signaling can be deconfigured, effectively unregistering the IRQ handler while still allowing eventfds to be signaled with a NULL context. This can occur either through the SET_IRQS ioctl or through the unmask irqfd process if the device interrupt is pending. The impact of this vulnerability is that an attacker could potentially cause the system to crash or become unstable.
Exploit Details
To exploit this vulnerability, an attacker would first need to be able to trigger the deconfiguration of the eventfd for INTx signaling. This could be done through the SET_IRQS ioctl, which is part of the vfio/pci subsystem, or by unmasking the irqfd if the device interrupt is pending.
Once the eventfd has been deconfigured, the attacker could then trigger a NULL context event, either directly or through the unmask irqfd process, causing the system to crash or become unstable.
The following code snippet demonstrates how the vulnerability exposes itself
static void vfio_intx_trigger(struct eventfd_ctx *eventfd, int n)
{
struct vfio_pci_intx *intx = eventfd_ctx_data(eventfd);
[...]
}
The above code shows that the eventfd could be triggered after deconfiguration with a NULL context, leading to the vulnerability.
Solution
To address this vulnerability, the Linux kernel developers have moved the configuration of the INTx interrupt handler to track the lifetime of the INTx context object and irq_type configuration, rather than registration of a particular trigger eventfd. This ensures that the eventfd trigger can be dynamically updated relative to in-flight interrupts or irqfd callbacks.
Original References
- Linux kernel commit
- LWN.net article
Conclusion
The CVE-2024-26812 vulnerability in the Linux kernel's vfio/pci subsystem has been resolved by implementing a solution that ensures proper synchronization between the ioctl path and eventfd_signal() wrapper. This will mitigate the risk of a potential crash or system instability stemming from this vulnerability. Users are advised to upgrade their Linux kernel to a version that includes the necessary patches.
Timeline
Published on: 04/05/2024 09:15:09 UTC
Last modified on: 12/19/2024 08:47:57 UTC