CVE-2025-39885
📋 TL;DR
This CVE describes a recursive semaphore deadlock vulnerability in the OCFS2 filesystem implementation in the Linux kernel. When performing a FIEMAP ioctl operation on a specially crafted mmap file, the kernel can deadlock due to recursive semaphore acquisition, causing a filesystem hang. This affects systems using the OCFS2 filesystem with vulnerable kernel versions.
💻 Affected Systems
- Linux kernel with OCFS2 filesystem support
📦 What is this software?
Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →Linux Kernel by Linux
The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...
Learn more about Linux Kernel →⚠️ Risk & Real-World Impact
Worst Case
Complete filesystem hang requiring system reboot, potentially causing service disruption and data corruption if writes are in progress.
Likely Case
Filesystem becomes unresponsive for specific operations, causing application failures and potential service disruption.
If Mitigated
Limited impact with proper monitoring and restart procedures in place.
🎯 Exploit Status
Requires local access and ability to create specially crafted mmap files on OCFS2 filesystem. Discovered by syzbot fuzzing.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Kernel versions with fixes from git commits: 04100f775c2e, 0709bc11b942, 16e518ca84df, 1d3c96547ee2, 36054554772f
Vendor Advisory: https://git.kernel.org/stable/c/04100f775c2ea501927f508f17ad824ad1f23c8d
Restart Required: Yes
Instructions:
1. Update Linux kernel to version containing the fix. 2. Check distribution-specific security advisories. 3. Reboot system to load new kernel.
🔧 Temporary Workarounds
Disable OCFS2
allIf OCFS2 is not required, disable it in kernel configuration or avoid mounting OCFS2 filesystems.
umount /path/to/ocfs2
modprobe -r ocfs2
Restrict FIEMAP operations
allLimit access to FIEMAP ioctl operations through SELinux/AppArmor policies or capability restrictions.
🧯 If You Can't Patch
- Monitor for filesystem hangs and implement automated recovery procedures
- Implement strict access controls to prevent unauthorized users from creating mmap files on OCFS2
🔍 How to Verify
Check if Vulnerable:
Check if OCFS2 filesystems are mounted: 'mount | grep ocfs2'. Check kernel version against affected ranges.Check Version:
uname -rVerify Fix Applied:
Verify kernel version includes fix commits. Test FIEMAP operations on OCFS2 filesystems.📡 Detection & Monitoring
Log Indicators:
- Kernel logs showing filesystem hangs
- Processes stuck in D state
- OCFS2 error messages
Network Indicators:
- N/A - local filesystem issue
SIEM Query:
Search for: 'kernel: ocfs2' AND 'deadlock' OR 'hang' in system logs🔗 References
- https://git.kernel.org/stable/c/04100f775c2ea501927f508f17ad824ad1f23c8d
- https://git.kernel.org/stable/c/0709bc11b942870fc0a7be150e42aea42321093a
- https://git.kernel.org/stable/c/16e518ca84dfe860c20a62f3615e14e8af0ace57
- https://git.kernel.org/stable/c/1d3c96547ee2ddeaddf8f19a3ef99ea06cc8115e
- https://git.kernel.org/stable/c/36054554772f95d090eb45793faf6aa3c0254b02
- https://git.kernel.org/stable/c/7e1514bd44ef68007703c752c99ff7319f35bce6
- https://git.kernel.org/stable/c/9efcb7a8b97310efed995397941a292cf89fa94f
- https://git.kernel.org/stable/c/ef30404980e4c832ef9bba1b10c08f67fa77a9ec
- https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html
