CVE-2026-80916kcov: fix data corruption and race conditions on PREEMPT_RT

Official description

In the Linux kernel, the following vulnerability has been resolved: kcov: fix data corruption and race conditions on PREEMPT_RT syzbot is reporting KCOV state corruption on PREEMPT_RT kernels, for the temporary storage used for saving/restoring remote KCOV state is currently allocated as the per-CPU area. On PREEMPT_RT kernels, softirq handlers run as preemptible task threads (e.g., ksoftirqd). If a softirq context preempts a task running a remote KCOV session, it safely saves the task's state into the per-CPU area. However, if that softirq thread is subsequently preempted by a higher- priority softirq thread on the same CPU, the second softirq will overwrite the same per-CPU area, permanently destroying the original task's KCOV state. Fix this data corruption by moving the temporary storage from the per-CPU area to the per-thread area. Since each softirq thread now owns its own task context, nested softirq preemption no longer causes data overwrites. Note that while the temporary storage is now on a per-thread basis, the per-CPU kcov_percpu_data.lock must be retained, for we need to ensure that kcov_remote_start() and kcov_remote_stop() operate atomically without racing against asynchronous interrupts that manipulate the current task's KCOV state. It is likely that GFP_KERNEL allocation by vmalloc_node() in kcov_init() has already called panic() before returning NULL, for there will be no OOM-killable userspace processes when __init function of built-in module runs. But this patch also fixes crashing the kernel when vmalloc_node() in kcov_init() returned NULL, for kcov_init() left per-CPU irq_area == NULL but kcov_remote_start() depends on per-CPU irq_area != NULL, resulting in (1) doing vmalloc() in kcov_remote_start() despite !in_task() context (2) out-of-array-bounds access if (1) succeeded but kcov->remote_size < CONFIG_KCOV_IRQ_AREA_SIZE (3) always leak memory allocated by (1), eventually killing all OOM-killable userspace processes problems.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/ef7048d8a614c5f5a9b20513a5428101a744514e
• https://git.kernel.org/stable/c/8ed3ddf23d39bf5338406bd9f8863d44748cf6ce
• https://git.kernel.org/stable/c/5dc59fc959b2b5742985d7ef24bccd1868217dc2
• https://git.kernel.org/stable/c/a2fb8222cde23b0001812ed3acb7c0ea36dd94e2
• https://git.kernel.org/stable/c/18799e858b407bf355383c9dd6c06477aa437134
• https://git.kernel.org/stable/c/e11f5b48c82703242a3be7a7ae4b4940b4cb4610
• https://git.kernel.org/stable/c/22670d1552fe155822b2abf91f920925f7d067b4
• https://git.kernel.org/stable/c/f8c9a3ec36b4ee3d4701b9be08f40e7bfbf89761
• https://git.kernel.org/stable/c/2eed77fdcb0cc48e8eccb2bcd4b7f2c6d650e84c