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.

Weakness

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.

Affected Software

Potential Mitigations

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