CVE-2025-21676: Addressing Linux Kernel Vulnerability in net:fec Handling page_pool_dev_alloc_pages Error

The Linux kernel is a very essential, and complex part of every Linux system. Ensuring its security and stability is critical to the overall performance of any Linux system. In this post, we look at an important vulnerability that has been resolved in the net:fec driver, specifically in handling page_pool_dev_alloc_pages error, and discuss the exploit details, along with the solution and code snippet.

Vulnerability and Exploit Details

A vulnerability was discovered in the Linux kernel's net:fec driver, specifically in the fec_enet_update_cbd function. The function called page_pool_dev_alloc_pages but did not properly handle the case when it returned NULL. Consequently, it triggered a WARN_ON(!new_page) message but proceeded to use the NULL pointer and eventually crashed.

This vulnerability was found to occur when the system was under memory pressure. One possible scenario to reproduce the issue had been observed when writing over a smbd share to a SATA HDD attached to an imx6q board.

Original Reference: Linux Kernel Mailing List

Solution and Code Snippet

To address this vulnerability, the Linux kernel contributors have provided a solution that involves handling the allocation error by dropping the current packet request. Here is the code snippet that shows the required update and handling of the allocation error:

static int fec_enet_update_cbd(struct fec_enet_private *fep, int index,
                struct sk_buff *skb)
{
    ...
    new_page = page_pool_dev_alloc_pages(pp); //<-- Call to page_pool_dev_alloc_pages
    if (unlikely(!new_page)) {
        /* Handle the allocation error by dropping the current packet request */
        netdev_err(ndev, "page allocation failed\n");
        fep->stats.tx_dropped++;
        return -ENOMEM;
    }
    ...
}

By making this change, the net:fec driver now correctly handles the memory allocation error and avoids crashing the system. This not only improves the stability of Linux systems but also prevents potential exploitation of the vulnerability.

For additional information and patches related to this issue, please check the Linux Kernel Mailing List.

Conclusion

The Linux kernel is a critical component of any Linux system and requires constant updates and security fixes. This post discussed CVE-2025-21676 and explained the vulnerability in the net:fec driver, along with the exploit details and the appropriate solution. By addressing the vulnerability and handling memory allocation errors properly, we can enhance the overall stability and security of our Linux systems.

Timeline

Published on: 01/31/2025 12:15:28 UTC
Last modified on: 02/04/2025 15:29:00 UTC