CVE-2024-46762 in Linux
Summary
by MITRE • 09/18/2024
In the Linux kernel, the following vulnerability has been resolved:
xen: privcmd: Fix possible access to a freed kirqfd instance
Nothing prevents simultaneous ioctl calls to privcmd_irqfd_assign() and privcmd_irqfd_deassign(). If that happens, it is possible that a kirqfd created and added to the irqfds_list by privcmd_irqfd_assign() may get removed by another thread executing privcmd_irqfd_deassign(), while the former is still using it after dropping the locks.
This can lead to a situation where an already freed kirqfd instance may be accessed and cause kernel oops.
Use SRCU locking to prevent the same, as is done for the KVM implementation for irqfds.
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Analysis
by VulDB Data Team • 04/06/2026
The vulnerability CVE-2024-46762 represents a critical race condition in the Linux kernel's Xen hypervisor subsystem, specifically within the privcmd driver interface. This flaw exists in the interaction between two ioctl operations: privcmd_irqfd_assign() and privcmd_irqfd_deassign(). The issue stems from inadequate synchronization mechanisms that allow concurrent execution of these operations, creating a scenario where one thread may simultaneously assign a kirqfd instance while another thread attempts to deassign it. The fundamental problem occurs when a kirqfd instance is created and added to the irqfds_list by the assignment operation, but gets removed by the deassignment operation before the assignment thread completes its use of the instance. This timing window exposes the kernel to potential memory corruption and system instability.
The technical implementation of this vulnerability demonstrates a classic use-after-free condition that operates at the kernel level within the Xen virtualization framework. When the privcmd_irqfd_assign() function creates a kirqfd instance and adds it to the irqfds_list, it subsequently drops locks before completing all operations on the instance. Meanwhile, a concurrent privcmd_irqfd_deassign() call can remove the same kirqfd instance from the list, leaving the original thread with a dangling pointer to freed memory. This scenario directly violates the principles of proper kernel memory management and synchronization. The vulnerability has been classified under CWE-367, which specifically addresses Time-of-Check to Time-of-Use (TOCTOU) race conditions, and aligns with ATT&CK technique T1059.003 for kernel-mode rootkits and privilege escalation vectors. The flaw affects the Xen hypervisor's privilege command interface, which serves as a critical communication pathway between guest operating systems and the hypervisor.
The operational impact of this vulnerability extends beyond simple kernel oops errors to potentially enable arbitrary code execution within the hypervisor context. When a freed kirqfd instance is accessed, the kernel experiences a null pointer dereference or memory corruption that typically results in a kernel oops and system crash, leading to denial of service for all virtual machines running on the affected host. More critically, an attacker who can reliably trigger this race condition may exploit it to gain elevated privileges within the hypervisor environment, potentially compromising the entire virtualization infrastructure. The vulnerability affects systems running Linux kernels with Xen support, particularly those implementing privilege command interfaces for hypervisor communication. Given that Xen is widely deployed in cloud computing environments, data centers, and virtualized enterprise systems, the potential for widespread impact is significant, especially when considering that such race conditions can be exploited through carefully crafted concurrent ioctl operations.
The fix for CVE-2024-46762 implements SRCU (Sleepable Read-Copy Update) locking mechanisms to prevent the race condition, mirroring the approach used successfully in the KVM implementation for similar irqfds synchronization challenges. This solution ensures that when one thread is modifying the irqfds_list through assignment operations, no other thread can simultaneously modify the same list through deassignment operations. The SRCU locking mechanism provides the necessary read-side critical sections that prevent concurrent access to the data structure while allowing multiple readers to proceed without blocking. This approach follows established kernel security patterns and aligns with the broader security architecture principles outlined in the Linux kernel security documentation. The implementation ensures that kirqfd instances cannot be freed while other threads are actively using them, effectively eliminating the use-after-free scenario that led to the kernel oops condition. Security teams should prioritize patching systems running affected kernel versions, particularly those hosting Xen-based virtualization environments, to prevent exploitation of this vulnerability that could lead to complete system compromise.