CVE-2026-72080 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
fs/resctrl: Fix use-after-free during unmount
During unmount or failure teardown all mon_data structures that contain monitoring event file private data are freed after which kernfs nodes are removed. However, the RDT_DELETED flag is never set for the statically allocated default resource group.
A concurrent reader of an event file associated with the default resource group may, after dropping kernfs active protection, block on rdtgroup_mutex while unmount proceeds to free the file private data and destroy the kernfs node without waiting for the reader.
When the mutex is released, the reader wakes up, observes that RDT_DELETED is not set for the default group, and dereferences the already-freed file private data.
The scenario can be depicted as follows: CPU0 CPU1 /* * Default resource group's * monitoring data accessible via * kernfs file with kernfs_node::priv * pointing to a struct mon_data. * User opens the file for reading. */ rdtgroup_mondata_show() /* arch encounters fatal error */ rdtgroup_kn_lock_live() resctrl_exit() atomic_inc(&rdtgroup_default.waitcount) cpus_read_lock() kernfs_break_active_protection(kn) mutex_lock(&rdtgroup_mutex) cpus_read_lock() resctrl_fs_teardown() mutex_lock(&rdtgroup_mutex) rmdir_all_sub() mon_put_kn_priv() /* Delete all mon_data structures */ rdtgroup_destroy_root() kernfs_destroy_root() rdtgroup_default.kn = NULL mutex_unlock(&rdtgroup_mutex) /* * rdtgroup_default.flags is empty so * rdtgroup_kn_lock_live() returns * &rdtgroup_default */ md = of->kn->priv;
/* md points to freed mon_data */
Set RDT_DELETED for the default group unconditionally since the flag does not lead to the freeing of this statically allocated group.
Do not allow a new resctrl mount if there are any waiters on default group of previous mount. A new mount will re-initialize the default group that would appear to waiters from previous mount as though the default group is accessible causing them to access the mon_data structures from the previous mount that have been removed.
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Analysis
by VulDB Data Team • 08/15/2026
The vulnerability described represents a critical use-after-free condition within the Linux kernel's resource control subsystem, specifically affecting the resctrl filesystem implementation. This issue manifests during the unmount process of the resctrl filesystem where monitoring data structures are improperly managed, creating opportunities for concurrent access to freed memory regions. The flaw occurs in the interaction between kernel filesystem operations and resource group management, particularly impacting how the default resource group handles cleanup operations when the filesystem is torn down.
The technical root cause stems from the improper handling of the RDT_DELETED flag for statically allocated default resource groups during filesystem teardown operations. When a resctrl filesystem instance is unmounted or encounters a failure condition, all monitoring data structures containing private file data are freed before the corresponding kernfs nodes are removed from the kernel's filesystem hierarchy. However, the default resource group's flags are never properly updated to indicate deletion status, leaving it in an inconsistent state where concurrent readers might access already-freed memory. This creates a race condition that can lead to kernel memory corruption and system instability.
The operational impact of this vulnerability extends beyond simple memory corruption to potentially enable privilege escalation or denial-of-service conditions within kernel space. Attackers could exploit this condition by carefully orchestrating concurrent file access operations during filesystem unmount events, causing the kernel to dereference freed memory structures. The scenario described involves a complex race condition where one CPU thread handles filesystem teardown while another accesses monitoring event files, leading to the kernel attempting to access memory that has already been deallocated. This type of vulnerability is particularly dangerous because it operates at kernel level where such errors can compromise system integrity and stability.
The mitigation strategy focuses on two primary approaches to prevent the use-after-free condition from occurring. First, the implementation must unconditionally set the RDT_DELETED flag for the default resource group during cleanup operations, ensuring that concurrent readers will properly detect when access to the resource group is no longer valid. Second, the system must prevent new resctrl mount operations when there are active waiters on the default group from previous mount instances, as this could cause the new mount to initialize structures that appear valid to stale waiters from the prior mount. This approach aligns with established security principles for preventing race conditions and memory corruption vulnerabilities in kernel code.
This vulnerability maps directly to CWE-416, which describes the use-after-free condition, and represents a classic example of improper resource management in kernel space. The ATT&CK framework categorizes this under privilege escalation techniques, specifically targeting kernel memory corruption as a method for gaining elevated privileges. The attack surface is particularly concerning given that resctrl filesystem operations are integral to modern Linux systems' resource management capabilities, especially in virtualized environments and containerized deployments where precise resource control is essential. Proper implementation of these mitigations ensures that the kernel maintains consistent state during filesystem operations while preventing concurrent access patterns that could lead to memory corruption. The fix reinforces proper synchronization mechanisms and resource lifecycle management, aligning with industry best practices for secure kernel development and maintaining system stability in multi-threaded environments where resource groups are actively managed and accessed concurrently.