CVE-2026-64290 in Linux
Summary
by MITRE • 07/25/2026
In the Linux kernel, the following vulnerability has been resolved:
iommufd: Break the loop on failure in iommufd_fault_fops_read()
On a copy_to_user() failure inside the inner list_for_each_entry, only the inner loop breaks; the outer while re-fetches the just-restored fault group and retries the failing copy_to_user() forever, spinning the reader at 100% CPU with fault->mutex held.
Check rc after the inner loop and break the outer while as well.
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Analysis
by VulDB Data Team • 07/25/2026
This vulnerability exists in the Linux kernel's iommufd subsystem where a critical flaw in the fault handling mechanism creates an infinite loop scenario that consumes excessive CPU resources. The issue occurs within the iommufd_fault_fops_read() function when processing memory faults for IOMMU (Input-Output Memory Management Unit) operations. When copy_to_user() fails during the processing of fault entries, the system only breaks out of the inner list_for_each_entry loop but continues executing the outer while loop, causing a continuous retry cycle that maintains exclusive access to the fault->mutex lock.
The technical implementation flaw stems from improper error handling within nested loop structures where the return code from copy_to_user() is not properly checked after the inner loop execution completes. This creates a scenario where fault groups are repeatedly re-fetched and processed without proper termination conditions when memory copying operations fail. The mutex remains locked throughout this process, preventing other threads from accessing the same fault data structure while the problematic thread spins indefinitely at 100% CPU utilization.
The operational impact of this vulnerability is severe as it results in a denial of service condition where legitimate system processes become starved of CPU resources due to the infinite loop. System administrators may observe sustained high CPU usage on specific threads related to IOMMU fault handling, potentially affecting system responsiveness and stability. The continuous spinning locks up the mutex, creating a bottleneck that prevents proper fault processing and can cascade into broader system performance degradation. This vulnerability affects systems utilizing IOMMU functionality for device memory management and virtualization scenarios where iommufd is actively processing fault conditions.
The fix involves checking the return code from the inner loop operations after execution completes, ensuring that when copy_to_user() fails, both the inner loop and outer while loop terminate appropriately rather than continuing the retry cycle. This remediation aligns with standard software engineering practices for error handling in nested loop structures and prevents resource exhaustion through proper termination conditions. The vulnerability can be classified under CWE-835 as an infinite loop without a counter or exit condition, and it relates to ATT&CK technique T1496 for resource exhaustion attacks. Proper implementation of error checking after nested operations prevents the escalation from a simple memory copy failure into a system-wide performance degradation scenario. Organizations should prioritize applying kernel updates that contain this fix to prevent exploitation and maintain system stability in virtualized environments where IOMMU functionality is actively utilized.