CVE-2022-33981: Linux Kernel Use-After-Free Vulnerability

CVE-2022-33981 Overview

CVE-2022-33981 is a Use-After-Free vulnerability in the Linux kernel's floppy disk driver (drivers/block/floppy.c). The flaw exists in the raw_cmd_ioctl function where a concurrency issue can lead to accessing memory after the raw_cmd structure has been deallocated. This vulnerability affects Linux kernel versions before 5.17.6 and can result in a denial of service condition on affected systems.

Critical Impact

Local attackers with low privileges can exploit this concurrency use-after-free flaw to cause a denial of service by triggering the race condition in the floppy driver's raw command handling functionality.

Affected Products

• Linux Kernel (versions before 5.17.6)
• Debian Linux 9.0
• Debian Linux 10.0

Discovery Timeline

• 2022-06-18 - CVE-2022-33981 published to NVD
• 2025-05-05 - Last updated in NVD database

Technical Details for CVE-2022-33981

Vulnerability Analysis

This vulnerability represents a classic race condition leading to a use-after-free memory corruption bug. The floppy disk driver in the Linux kernel contains a flaw in how it handles raw command ioctl operations. When the raw_cmd_ioctl function processes requests, there exists a window where the raw_cmd structure can be deallocated while still being referenced by concurrent operations.

The use-after-free condition occurs because the driver does not properly synchronize access to the raw_cmd memory structure. When one thread deallocates this structure while another thread still holds a reference to it, subsequent access attempts will operate on freed memory, leading to unpredictable behavior and potential system crashes.

Root Cause

The root cause of CVE-2022-33981 is improper synchronization in the raw_cmd_ioctl function within drivers/block/floppy.c. The code path that handles raw floppy disk commands lacks adequate locking mechanisms to prevent concurrent access during deallocation. This allows a race condition where the raw_cmd structure can be freed by one execution path while another path is still using it.

The FDRAWCMD ioctl interface, which provides low-level hardware access to floppy drives, was identified as rarely used and potentially unstable, prompting the kernel maintainers to deprecate this functionality entirely.

Attack Vector

Exploitation requires local access to the system with low-level privileges. An attacker would need to trigger the race condition by sending carefully timed ioctl requests to the floppy driver. The attack does not require user interaction and operates within the local system context.

The vulnerability is limited to systems that have floppy drive support enabled in the kernel and where the attacker can interact with the floppy device interface. The impact is constrained to denial of service (availability impact) with no confidentiality or integrity compromise.

 	  To compile this driver as a module, choose M here: the
 	  module will be called floppy.
 
+config BLK_DEV_FD_RAWCMD
+	bool "Support for raw floppy disk commands (DEPRECATED)"
+	depends on BLK_DEV_FD
+	help
+	  If you want to use actual physical floppies and expect to do
+	  special low-level hardware accesses to them (access and use
+	  non-standard formats, for example), then enable this.
+
+	  Note that the code enabled by this option is rarely used and
+	  might be unstable or insecure, and distros should not enable it.
+
+	  Note: FDRAWCMD is deprecated and will be removed from the kernel
+	  in the near future.
+
+	  If unsure, say N.
+
 config AMIGA_FLOPPY
 	tristate "Amiga floppy support"
 	depends on AMIGA

Source: GitHub Linux Commit

Detection Methods for CVE-2022-33981

Indicators of Compromise

• Unexpected kernel crashes or system hangs related to the floppy driver subsystem
• Kernel oops messages referencing floppy.c or raw_cmd_ioctl in system logs
• Abnormal ioctl calls to /dev/fd* devices from unprivileged processes
• Memory corruption warnings in kernel logs associated with the block device layer

Detection Strategies

• Monitor kernel logs (dmesg, /var/log/kern.log) for use-after-free warnings or crashes in the floppy driver
• Implement audit rules to track ioctl system calls targeting floppy device nodes
• Use kernel address sanitizer (KASAN) during testing to detect use-after-free conditions
• Deploy runtime integrity monitoring to detect suspicious interactions with deprecated floppy interfaces

Monitoring Recommendations

• Configure centralized logging to capture kernel messages from all endpoints
• Set up alerts for kernel oops events mentioning floppy.c or related driver components
• Monitor for unusual access patterns to legacy block devices (/dev/fd*)
• Implement SentinelOne Singularity platform for real-time kernel-level threat detection

How to Mitigate CVE-2022-33981

Immediate Actions Required

• Update the Linux kernel to version 5.17.6 or later where the fix is included
• Apply vendor-specific patches for Debian systems (DSA-5173)
• Disable the floppy driver module if not required: modprobe -r floppy
• Restrict access to floppy device nodes using appropriate file permissions

Patch Information

The vulnerability has been addressed in Linux kernel version 5.17.6. The fix introduces a new kernel configuration option CONFIG_BLK_DEV_FD_RAWCMD which disables the vulnerable FDRAWCMD functionality by default. The raw command interface is now deprecated and will be removed in future kernel releases.

Relevant patches and advisories:

• Linux Kernel ChangeLog 5.17.6
• GitHub Linux Commit
• Debian Security Advisory DSA-5173
• Debian LTS Announcement

Workarounds

• Blacklist the floppy module to prevent loading: add blacklist floppy to /etc/modprobe.d/blacklist.conf
• Remove the floppy kernel module entirely if floppy drive support is not needed
• Restrict device node permissions to prevent unprivileged access to /dev/fd*
• Rebuild the kernel without CONFIG_BLK_DEV_FD_RAWCMD enabled

# Configuration example
# Blacklist the floppy driver module
echo "blacklist floppy" | sudo tee /etc/modprobe.d/blacklist-floppy.conf

# Remove the module if currently loaded
sudo modprobe -r floppy

# Verify the module is not loaded
lsmod | grep floppy

# Restrict access to floppy device nodes (if they exist)
sudo chmod 600 /dev/fd* 2>/dev/null || true