CVE-2026-89909 in Linux
Summary
by MITRE • 09/16/2026
In the Linux kernel, the following vulnerability has been resolved:
LoongArch: KVM: Free init resources if kvm_init() fails
kvm_loongarch_init() calls kvm_loongarch_env_init() to allocate the per-CPU kvm_context (vmcs) and kvm_loongarch_ops and to register the perf callbacks, and then calls kvm_init(). If kvm_init() fails its result is returned directly, but since module_init() does not run the module_exit() stuff on failure, so kvm_loongarch_env_exit() is never called and those resources are leaked.
So call kvm_loongarch_env_exit() when kvm_init() fails, matching the teardown-on-failure pattern used by riscv_kvm_init().
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Analysis
by VulDB Data Team • 09/16/2026
The Linux kernel's KVM subsystem for LoongArch architecture contains a resource management flaw within its initialization sequence that leads to memory leaks and potential instability during module loading. This vulnerability arises from an asymmetry in error handling logic where the cleanup procedures are not executed if the primary initialization function fails. Specifically, the kvm_loongarch_init function is responsible for setting up critical infrastructure including per-CPU context structures known as vmcs, initializing operation vectors via kvm_loangarch_ops, and registering performance monitoring callbacks through perf interfaces. These steps involve allocating kernel memory and establishing state that must be properly released if subsequent initialization stages do not complete successfully.
The core technical flaw occurs when the function calls kvm_init to register the virtual machine monitor with the broader KVM framework. If this call returns an error code indicating failure, the current implementation immediately propagates this return value without invoking the corresponding teardown routine, kvm_loongarch_env_exit. In standard Linux kernel module development, if a module initialization function fails, the kernel does not automatically invoke the associated exit or cleanup functions because it assumes the module was never successfully loaded into memory. Consequently, any resources allocated prior to the failure point remain resident in kernel space indefinitely until system reboot. This constitutes an improper resource deallocation scenario where dynamic allocations are not freed upon abnormal termination paths.
From a security and stability perspective, this vulnerability falls under CWE-401 which describes missing release of memory after effective usage. While a single instance might seem negligible, repeated attempts to load or reload the module in environments with frequent configuration changes can lead to cumulative kernel memory exhaustion. Over time, such leaks contribute to increased pressure on the slab allocator and may eventually trigger out-of-memory conditions within critical subsystems, potentially causing system-wide instability or denial of service for other processes relying on available kernel resources. Furthermore, stale pointers from partially initialized contexts could theoretically be accessed if error handling paths are complex, although in this specific case the primary risk is resource exhaustion rather than arbitrary code execution.
This issue aligns with ATT&CK technique T1496 which relates to Resource Hijacking through denial of service via resource consumption. By failing to clean up after a failed initialization attempt, an attacker or misconfigured system component can trigger repeated allocations without corresponding deallocations. Although the vulnerability requires root privileges to load kernel modules in most distributions, it highlights a lack of robustness in error handling paths that should be addressed for production-grade stability. The fix involves ensuring that kvm_loarch_env_exit is called whenever kvm_init fails, thereby mirroring the teardown-on-failure pattern already established by other architectures such as RISC-V KVM initialization routines.
Mitigation strategies primarily involve applying the upstream kernel patch that corrects this control flow logic. Administrators should ensure their systems are updated to a version of the Linux kernel where this fix is included. For environments unable to update immediately, restricting module loading capabilities and auditing dmesg logs for kvm-related errors can help monitor for signs of resource leakage. Long-term remediation requires rigorous code review practices that enforce symmetric initialization and cleanup sequences across all architecture-specific KVM implementations within the mainline kernel tree.