CVE-2023-53624
📋 TL;DR
This CVE describes an integer overflow vulnerability in the Linux kernel's sch_fq (Fair Queue) packet scheduler. When configured with 'initial quantum' values greater than INT_MAX, the 'credit' variable overflows to a large negative value, potentially causing CPU soft-lockup warnings and performance degradation. This affects Linux systems using the sch_fq scheduler with specific configurations.
💻 Affected Systems
- Linux kernel
⚠️ Risk & Real-World Impact
Worst Case
CPU soft-lockup leading to system instability, denial of service, and potential performance degradation affecting network traffic processing.
Likely Case
Performance degradation and CPU soft-lockup warnings when sch_fq is configured with large initial quantum values, potentially affecting network throughput.
If Mitigated
Minimal impact if sch_fq is not used or configured with safe initial quantum values below INT_MAX.
🎯 Exploit Status
Syzkaller script exists to trigger the issue, but exploitation requires ability to configure network scheduler parameters (typically requires root/admin access).
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Kernel versions with commits: 2322462d6f9ad4874f4e3c63df3b5cc00cb1acbd, 4b8a05e3801661a0438fcd0cdef181030d966a5a, 4fbefeab88c6e79753a25099d455d3d59d2946b4, 7041101ff6c3073fd8f2e99920f535b111c929cb, 85f24cb2f10b2b0f2882e5786a09b4790bb3a0ad
Vendor Advisory: https://git.kernel.org/stable/c/2322462d6f9ad4874f4e3c63df3b5cc00cb1acbd
Restart Required: Yes
Instructions:
1. Update Linux kernel to patched version from your distribution vendor. 2. Reboot system to load new kernel. 3. Verify kernel version after reboot.
🔧 Temporary Workarounds
Limit initial quantum value
linuxConfigure sch_fq with initial quantum values below INT_MAX (2,147,483,647)
tc qdisc add dev <interface> root fq initial_quantum 2147483647
Disable sch_fq scheduler
linuxUse alternative network schedulers instead of sch_fq
tc qdisc del dev <interface> root
tc qdisc add dev <interface> root pfifo_fast
🧯 If You Can't Patch
- Monitor system logs for CPU soft-lockup warnings related to network scheduling
- Audit and restrict sch_fq configuration to prevent large initial quantum values
🔍 How to Verify
Check if Vulnerable:
Check if sch_fq is configured with initial quantum > INT_MAX: tc qdisc show | grep -A5 'fq'Check Version:
uname -rVerify Fix Applied:
Check kernel version includes fix commits and verify sch_fq configuration uses safe values📡 Detection & Monitoring
Log Indicators:
- CPU soft-lockup warnings in kernel logs (dmesg)
- Performance degradation in network throughput
Network Indicators:
- Unusual network latency or packet loss when sch_fq is active
SIEM Query:
source="kernel" AND "soft lockup" AND ("CPU" OR "scheduler")🔗 References
- https://git.kernel.org/stable/c/2322462d6f9ad4874f4e3c63df3b5cc00cb1acbd
- https://git.kernel.org/stable/c/4b8a05e3801661a0438fcd0cdef181030d966a5a
- https://git.kernel.org/stable/c/4fbefeab88c6e79753a25099d455d3d59d2946b4
- https://git.kernel.org/stable/c/7041101ff6c3073fd8f2e99920f535b111c929cb
- https://git.kernel.org/stable/c/85f24cb2f10b2b0f2882e5786a09b4790bb3a0ad
- https://git.kernel.org/stable/c/d0b43125ec892aeb1b03e5df5aab595097da225a
