CVE-2022-50549
📋 TL;DR
This CVE describes an ABBA deadlock vulnerability in the Linux kernel's device-mapper thin provisioning subsystem. When specific concurrent operations occur (like dropping caches while thin provisioning metadata operations fail), the system can enter a deadlock state causing hung tasks and potential denial of service. This affects Linux systems using device-mapper thin provisioning.
💻 Affected Systems
- Linux kernel
⚠️ Risk & Real-World Impact
Worst Case
System becomes completely unresponsive with hung tasks, requiring hard reboot and potentially causing data corruption or service disruption.
Likely Case
Partial system hang affecting specific processes, degraded performance, and potential service interruption until deadlock is resolved.
If Mitigated
Minor performance impact or temporary process blocking that resolves automatically.
🎯 Exploit Status
Exploitation requires specific timing and conditions (concurrent drop cache operations and thin provisioning metadata failures). Not a typical remote exploit.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Fixed in kernel commits: 200aa33b5d781e7c0fa6c0c7db9dbcc3f574ce8f, 2d891cc5a1706b6908bceb56af7176a463ee6d62, 7e37578069737b04955c71dd85db8a3bc2709eff, 8111964f1b8524c4bb56b02cd9c7a37725ea21fd, cdf7a39bcc427febbfe3c3b9fe829825ead96c27
Vendor Advisory: https://git.kernel.org/stable/c/200aa33b5d781e7c0fa6c0c7db9dbcc3f574ce8f
Restart Required: Yes
Instructions:
1. Update Linux kernel to version containing the fix commits. 2. Check your distribution's security advisories for specific patched kernel versions. 3. Reboot system after kernel update.
🔧 Temporary Workarounds
Avoid drop_caches operations
linuxPrevent triggering the deadlock by avoiding 'echo 3 > /proc/sys/vm/drop_caches' operations on systems using dm-thin.
# Monitor and restrict drop_caches usage
# Consider setting vm.drop_caches=0 in sysctl
Disable dm-thin if not needed
linuxIf device-mapper thin provisioning is not required, disable or remove the dm-thin module.
# Check if dm-thin is loaded: lsmod | grep dm_thin
# Unload module: modprobe -r dm_thin
# Blacklist module: echo 'blacklist dm_thin' > /etc/modprobe.d/disable-dm-thin.conf
🧯 If You Can't Patch
- Monitor system for hung tasks and deadlock symptoms in kernel logs
- Implement process monitoring to detect and restart hung services automatically
🔍 How to Verify
Check if Vulnerable:
Check kernel version and if dm-thin is in use: uname -r && lsmod | grep dm_thinCheck Version:
uname -rVerify Fix Applied:
Verify kernel version includes the fix commits or check with distribution-specific security tools📡 Detection & Monitoring
Log Indicators:
- Kernel logs showing 'blocked for more than 15 seconds'
- 'INFO: task ... blocked' messages
- Hung task warnings in dmesg
Network Indicators:
- None - this is a local kernel issue
SIEM Query:
source="kernel" AND ("blocked for more than" OR "hung task" OR "ABBA deadlock")🔗 References
- https://git.kernel.org/stable/c/200aa33b5d781e7c0fa6c0c7db9dbcc3f574ce8f
- https://git.kernel.org/stable/c/2d891cc5a1706b6908bceb56af7176a463ee6d62
- https://git.kernel.org/stable/c/7e37578069737b04955c71dd85db8a3bc2709eff
- https://git.kernel.org/stable/c/8111964f1b8524c4bb56b02cd9c7a37725ea21fd
- https://git.kernel.org/stable/c/cdf7a39bcc427febbfe3c3b9fe829825ead96c27
- https://git.kernel.org/stable/c/f8c26c33fef588ee54852cffa7cbb9f9d9869405
