CVE-2023-54239: 
Linux Kernel vulnerability analysis and mitigation

CVE-2023-54239 is a vulnerability in the Linux kernel's iommufd subsystem where insufficient validation of user-supplied virtual address (uptr) and size parameters can cause an integer overflow, triggering kernel WARN_ON conditions. The flaw was discovered via syzkaller fuzzing and affects Linux kernel versions prior to the fix being applied. It was published to NVD on December 30, 2025. The CVSS score and severity rating are not yet publicly assigned (Feedly).

The root cause is an integer overflow (CWE-190) in the iommufd pages subsystem (drivers/iommu/iommufd/pages.c). When a user-space process sets up an IOMMU mapping with a virtual address (uptr) and size that together wrap past zero (i.e., uptr + size overflows), the kernel does not detect the invalid range before passing it to pin_user_pages. This causes pin_user_pages to receive invalid arguments and return 0 unexpectedly, triggering a WARN_ON at pfn_reader_user_pin+0x2e6/0x390. The fix adds an overflow check to prevent creation of page mappings with such invalid address/size combinations (Feedly, Kernel Fix 1, Kernel Fix 2).

Exploitation of this vulnerability by a local user with access to the iommufd interface can trigger kernel WARN_ON conditions, potentially causing a kernel panic or denial of service. Because the overflow occurs in the IOMMU page-pinning path, it may also lead to unpredictable kernel behavior affecting system stability and availability. Confidentiality and integrity impacts are not clearly established based on available information (Feedly).

1. Prerequisite: Obtain local access to a Linux system with a vulnerable kernel version that exposes the iommufd interface to unprivileged or low-privileged users.
2. Craft malicious mapping request: Prepare an iommufd IOAS mapping request with a user virtual address (uptr) and size value chosen such that uptr + size wraps past zero (integer overflow).
3. Submit the request: Use the appropriate iommufd ioctl (e.g., IOMMU_IOAS_MAP) to submit the crafted mapping to the kernel.
4. Trigger overflow: The kernel, lacking the overflow check, passes the invalid address range to pin_user_pages, which returns 0 due to invalid arguments.
5. Kernel instability: The WARN_ON at pfn_reader_user_pin is triggered, potentially causing a kernel panic or denial of service (Feedly).

• Logs: Kernel logs (dmesg) showing WARNING: CPU: X PID: X at drivers/iommu/iommufd/pages.c:793 pfn_reader_user_pin+0x2e6/0x390 with associated stack traces.
• Process: Unusual processes making repeated iommufd-related ioctl calls, particularly with crafted or boundary-value address/size parameters.
• System Behavior: Unexpected kernel panics or system reboots on systems with IOMMU/iommufd enabled.

Apply the upstream Linux kernel patches that add overflow checks for uptr + size in the iommufd pages subsystem. The fixes are available at the stable kernel tree commits 800963e7eb001ada8cf2418f159fb649694467f1 and e4395701330fc4aee530905039516fe770b81417. Administrators should update to a patched kernel version as soon as their distribution provides one. As a temporary workaround, restricting unprivileged access to the iommufd interface can reduce exposure (Kernel Fix 1, Kernel Fix 2).