CVE-2026-80866 in Linux
Summary
by MITRE • 09/04/2026
In the Linux kernel, the following vulnerability has been resolved:
tipc: avoid busy looping in tipc_exit_net()
Blamed commit introduced a busy-wait loop in tipc_exit_net() to wait for pending UDP bearer cleanup works to complete:
while (atomic_read(&tn->wq_count)) cond_resched();
This loop can busy-wait for a long time if cond_resched() is a NOP. This typically happens if the netns exit is executed by a high priority task, or under kernels configured without preemption (CONFIG_PREEMPT_NONE). In such cases, it wastes CPU cycles and can lead to soft lockups.
Fix this by replacing the busy loop with wait_var_event(), allowing the thread to sleep properly until the work queue count reaches zero.
Accordingly, update cleanup_bearer() to use atomic_dec_and_test() and wake_up_var() to wake up the waiter when the count drops to zero.
This uses the global wait queue hash table, avoiding the need to bloat struct tipc_net with a wait_queue_head_t. The atomic_dec_and_test() provides the necessary memory barrier to ensure the wakeup is not missed.
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Analysis
by VulDB Data Team • 09/04/2026
The Linux kernel's Transparent Inter-Process Communication (TIPC) subsystem contained a performance and stability defect within its network namespace exit routine, specifically in the tipc_exit_net function. This issue originated from an earlier commit that introduced a busy-wait loop to ensure pending UDP bearer cleanup work items were fully completed before proceeding with resource deallocation. The original implementation utilized a while loop checking an atomic counter of queued work items, interspersed with calls to cond_resched() to yield the CPU. While this approach functions correctly under standard preemptible kernel configurations, it fails catastrophically in environments where preemption is disabled or when executed by high-priority real-time tasks. In such scenarios, cond_resched() becomes a no-op because the scheduler cannot interrupt the current execution context to switch threads. Consequently, the loop spins continuously without yielding CPU time, leading to significant resource waste and potential system instability.
The operational impact of this vulnerability is severe for systems running kernels with CONFIG_PREEMPT_NONE or those utilizing high-priority scheduling policies. The continuous spinning consumes 100 percent of a CPU core's cycles indefinitely until the background work completes, which may take an unpredictable amount of time depending on system load and I/O latency. This behavior classifies as a denial-of-service condition against local resources, effectively causing soft lockups where other processes are starved of CPU time despite the kernel remaining technically responsive to interrupts. From a vulnerability classification perspective, this aligns with CWE-835, which describes loops that busy-wait instead of blocking or sleeping appropriately, and relates to ATT&CK technique T1496, Resource Hijacking, as it allows for the monopolization of computational resources through inefficient synchronization primitives.
The resolution involves replacing the ineffective busy-loop mechanism with a proper sleep-based wait condition using the wait_var_event macro. This change ensures that when no pending work remains or while waiting for such completion, the executing thread enters an interruptible sleep state rather than spinning on the CPU. To support this transition, the cleanup_bearer function was updated to utilize atomic_dec_and_test() combined with wake_up_var(). The use of atomic operations provides the necessary memory barriers to guarantee that updates to the work queue count are visible to waiting threads before they check for completion. Furthermore, by leveraging a global wait queue hash table instead of embedding a dedicated wait_queue_head_t structure within each tipc_net instance, the patch optimizes memory usage and avoids bloating kernel data structures while maintaining robust synchronization semantics across different network namespaces.