Overview
CVE-2025-40239 describes a critical vulnerability affecting the LAN8814 PHY driver within the Linux kernel. This vulnerability, if unaddressed, can lead to a null pointer dereference, potentially causing a kernel crash and system instability. The patch resolves the issue by ensuring the shared->phydev pointer is always initialized, regardless of PTP clock setup success.
Technical Details
The root cause of the vulnerability lies within the LAN8814 PTP probe function. Previously, the shared->phydev member was only set if the PTP clock was successfully configured. However, the lan8814_gpio_process_cap function, executed during IRQ handling, unconditionally accesses shared->phydev. If the PTP clock configuration failed, shared->phydev would remain NULL, leading to a null pointer dereference when accessed by lan8814_gpio_process_cap.
The fix ensures that shared->phydev is always initialized, even if the PTP clock setup fails, thereby preventing the null pointer dereference.
Affected Code Snippet (Before Patch – Illustrative):
// Simplified illustration of the vulnerable logic
if (ptp_clock_register(dev, &ptp_clock_info) == 0) {
shared->phydev = phydev; // phydev assigned ONLY on successful PTP registration
}
// ... Later in IRQ handling
lan8814_gpio_process_cap(shared->phydev); // Potential NULL pointer dereference if ptp_clock_register failed
CVSS Analysis
Due to the potential for a kernel crash, this vulnerability is considered serious. However, due to factors such as exploitability and impact scope, the CVSS score is currently listed as N/A. A more detailed CVSS analysis may be published at a later date.
Possible Impact
A successful exploitation of this vulnerability can result in the following:
- Kernel crash
- System instability
- Denial of Service (DoS)
Mitigation or Patch Steps
The recommended mitigation is to apply the patch that addresses this vulnerability. The patch is available in the stable kernel tree. Users should update their Linux kernel to a version containing the fix. This fix has been backported to multiple stable kernel branches.
Update your system using your distribution’s package manager (e.g., apt update && apt upgrade on Debian/Ubuntu, yum update on CentOS/RHEL, pacman -Syu on Arch Linux).
