CVE-2022-29968: Linux Kernel Initialization Vulnerability

CVE-2022-29968 Overview

CVE-2022-29968 is an Uninitialized Memory Use vulnerability discovered in the Linux kernel through version 5.17.5. The flaw exists in the io_rw_init_file function within fs/io_uring.c, where the kiocb->private field is not properly initialized. This uninitialized memory condition can potentially allow a local attacker to achieve privilege escalation or cause information disclosure by exploiting the undefined state of the memory.

Critical Impact

Local attackers with low privileges can exploit uninitialized memory in the io_uring subsystem to potentially achieve high confidentiality, integrity, and availability impact on affected Linux systems.

Affected Products

• Linux Kernel (through version 5.17.5)
• Fedora 34, 35, and 36
• NetApp H300S/H500S/H700S/H410S/H410C Firmware
• NetApp SolidFire & HCI Management Node

Discovery Timeline

• May 2, 2022 - CVE-2022-29968 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2022-29968

Vulnerability Analysis

This vulnerability is classified under CWE-909 (Missing Initialization of Resource), indicating a failure to properly initialize a critical data structure before use. The flaw resides in the io_uring subsystem, specifically in the io_rw_init_file function located in fs/io_uring.c.

The io_uring interface is a high-performance asynchronous I/O mechanism in the Linux kernel designed to reduce system call overhead. During the initialization of read/write operations with I/O polling enabled, the kernel allocates a kiocb (kernel I/O control block) structure to track the operation. However, the code path failed to initialize the private field of this structure when setting up IOPOLL operations.

When the IOCB_HIPRI flag is set (indicating high-priority I/O polling), the uninitialized kiocb->private pointer could contain arbitrary memory contents from previous allocations. This creates conditions where subsequent code paths that reference this field may operate on undefined data, potentially leading to information leakage or memory corruption.

Root Cause

The root cause is the missing initialization of the kiocb->private field in the io_rw_init_file function. When processing I/O requests with direct I/O and I/O polling (iopoll) enabled, the function sets various flags and the completion callback but neglects to set kiocb->private to a known safe value (NULL). This is a classic case of an uninitialized memory bug where the kernel assumes memory will be in a clean state but fails to explicitly ensure it.

Attack Vector

The attack requires local access to the system with low privileges. An attacker would need to:

1. Have the ability to execute code on the target system
2. Open a file that supports direct I/O operations
3. Submit io_uring requests with the IOCB_HIPRI flag to trigger the IOPOLL code path
4. Exploit the uninitialized memory state in kiocb->private to leak information or corrupt memory

The vulnerability requires no user interaction to exploit once an attacker has local access.

// Security patch from fs/io_uring.c
// Source: https://github.com/torvalds/linux/commit/32452a3eb8b64e01e2be717f518c0be046975b9d

 		if (!(kiocb->ki_flags & IOCB_DIRECT) || !file->f_op->iopoll)
 			return -EOPNOTSUPP;
 
+		kiocb->private = NULL;
 		kiocb->ki_flags |= IOCB_HIPRI | IOCB_ALLOC_CACHE;
 		kiocb->ki_complete = io_complete_rw_iopoll;
 		req->iopoll_completed = 0;

The fix explicitly initializes kiocb->private to NULL before the subsequent flag assignments, ensuring the field is in a known safe state.

Detection Methods for CVE-2022-29968

Indicators of Compromise

• Unusual io_uring system call patterns, particularly with high-priority I/O polling enabled
• Unexpected kernel memory access patterns or kernel oops messages related to io_uring
• Applications making excessive use of io_uring_setup and io_uring_enter syscalls with IOPOLL flags
• Kernel log entries indicating memory corruption in io_uring subsystem components

Detection Strategies

• Monitor for processes making abnormal io_uring system calls with IORING_SETUP_IOPOLL flag
• Implement kernel auditing to track io_uring operations from unprivileged users
• Deploy endpoint detection solutions capable of identifying kernel exploitation attempts
• Use Linux Audit framework to log io_uring syscall activity on critical systems

Monitoring Recommendations

• Enable comprehensive system call auditing for io_uring operations (io_uring_setup, io_uring_enter, io_uring_register)
• Monitor /proc/[pid]/io for unusual I/O patterns that may indicate exploitation attempts
• Review kernel dmesg logs for warnings or errors related to io_uring or kiocb structures
• Implement real-time process monitoring to detect suspicious privilege escalation attempts

How to Mitigate CVE-2022-29968

Immediate Actions Required

• Update Linux kernel to a version containing commit 32452a3eb8b64e01e2be717f518c0be046975b9d or later
• Apply vendor-specific patches from Fedora or NetApp as applicable to your environment
• Restrict access to systems running vulnerable kernel versions to trusted users only
• Consider disabling io_uring functionality if not required by setting io_uring_disabled sysctl to 2

Patch Information

The vulnerability has been addressed in the upstream Linux kernel through commit 32452a3eb8b64e01e2be717f518c0be046975b9d. Fedora has released updates for versions 34, 35, and 36 through their package announcement channels. NetApp has also issued a security advisory for affected products including H300S, H500S, H700S, H410S, H410C firmware, and SolidFire & HCI Management Node.

Workarounds

• Disable io_uring system-wide by setting kernel.io_uring_disabled=2 via sysctl
• Use seccomp filters to block io_uring syscalls for untrusted applications
• Restrict local user access to minimize the attack surface until patching is complete
• Implement container isolation with io_uring restrictions for workloads that don't require it

# Configuration example - Disable io_uring system-wide
# Add to /etc/sysctl.conf or /etc/sysctl.d/99-disable-io_uring.conf
echo "kernel.io_uring_disabled = 2" | sudo tee /etc/sysctl.d/99-disable-io_uring.conf
sudo sysctl -p /etc/sysctl.d/99-disable-io_uring.conf

# Verify the setting is applied
sysctl kernel.io_uring_disabled