CVE-2025-39945

In the Linux kernel, the following vulnerability has been resolved:

cnic: Fix use-after-free bugs in cnic_delete_task

The original code uses cancel_delayed_work() in cnic_cm_stop_bnx2x_hw(), which does not guarantee that the delayed work item delete_task has fully completed if it was already running. Additionally, the delayed work item is cyclic, the flush_workqueue() in cnic_cm_stop_bnx2x_hw() only blocks and waits for work items that were already queued to the workqueue prior to its invocation. Any work items submitted after flush_workqueue() is called are not included in the set of tasks that the flush operation awaits. This means that after the cyclic work items have finished executing, a delayed work item may still exist in the workqueue. This leads to use-after-free scenarios where the cnic_dev is deallocated by cnic_free_dev(), while delete_task remains active and attempt to dereference cnic_dev in cnic_delete_task().

A typical race condition is illustrated below:

CPU 0 (cleanup) | CPU 1 (delayed work callback) cnic_netdev_event() | cnic_stop_hw() | cnic_delete_task() cnic_cm_stop_bnx2x_hw() | … cancel_delayed_work() | /* the queue_delayed_work() flush_workqueue() | executes after flush_workqueue()*/ | queue_delayed_work() cnic_free_dev(dev)//free | cnic_delete_task() //new instance | dev = cp->dev; //use

Replace cancel_delayed_work() with cancel_delayed_work_sync() to ensure that the cyclic delayed work item is properly canceled and that any ongoing execution of the work item completes before the cnic_dev is deallocated. Furthermore, since cancel_delayed_work_sync() uses __flush_work(work, true) to synchronously wait for any currently executing instance of the work item to finish, the flush_workqueue() becomes redundant and should be removed.

This bug was identified through static analysis. To reproduce the issue and validate the fix, I simulated the cnic PCI device in QEMU and introduced intentional delays — such as inserting calls to ssleep() within the cnic_delete_task() function — to increase the likelihood of triggering the bug.

Affected Software

References

• https://git.kernel.org/stable/c/0405055930264ea8fd26f4131466fa7652e5e47d
• https://git.kernel.org/stable/c/0627e1481676669cae2df0d85b5ff13e7d24c390
• https://git.kernel.org/stable/c/6e33a7eed587062ca8161ad1f4584882a860d697
• https://git.kernel.org/stable/c/7b6a5b0a6b392263c3767fc945b311ea04b34bbd
• https://git.kernel.org/stable/c/8eeb2091e72d75df8ceaa2172638d61b4cf8929a
• https://git.kernel.org/stable/c/cfa7d9b1e3a8604afc84e9e51d789c29574fb216
• https://git.kernel.org/stable/c/e1fcd4a9c09feac0902a65615e866dbf22616125
• https://git.kernel.org/stable/c/fde6e73189f40ebcf0633aed2b68e731c25f3aa3