CVE-2020-29374: Linux Kernel Privilege Escalation Flaw

CVE-2020-29374 Overview

An issue was discovered in the Linux kernel before 5.7.3, related to mm/gup.c and mm/huge_memory.c. The get_user_pages (aka gup) implementation, when used for a copy-on-write page, does not properly consider the semantics of read operations and therefore can grant unintended write access. This vulnerability is tracked as CID-17839856fd58.

Critical Impact

This race condition vulnerability in Linux kernel memory management could allow local attackers with low privileges to gain unintended write access to memory pages that should be read-only, potentially leading to data corruption or information disclosure.

Affected Products

• Linux kernel versions before 5.7.3
• Debian Linux 9.0 and 10.0
• NetApp 500f, A250, and H410C firmware
• NetApp SolidFire & HCI Management Node
• NetApp SolidFire & HCI Storage Node
• NetApp HCI Compute Node BIOS

Discovery Timeline

• 2020-06-25 - Linux kernel 5.7.3 released with security patch
• 2020-11-28 - CVE-2020-29374 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-29374

Vulnerability Analysis

This vulnerability exists in the Linux kernel's memory management subsystem, specifically within the get_user_pages (GUP) implementation. The flaw relates to how the kernel handles copy-on-write (CoW) pages during certain memory access operations.

The core issue stems from improper handling of read operation semantics when dealing with CoW pages. Under normal circumstances, when a process attempts to write to a CoW page, the kernel should create a private copy of that page for the writing process. However, due to this vulnerability, the GUP implementation can incorrectly grant write permissions to pages that should remain read-only.

This race condition (CWE-362) occurs between the time when memory access permissions are checked and when the actual memory operation is performed. An attacker who can precisely time their operations could exploit this window to gain write access to memory regions they should only be able to read. The issue was identified by Google's Project Zero team and documented in their bug tracker.

Root Cause

The root cause lies in the get_user_pages function's failure to properly validate and enforce copy-on-write semantics during read operations. The GUP mechanism is used extensively in the kernel for direct memory access scenarios, including I/O operations and memory pinning. When handling CoW pages, the implementation did not correctly account for scenarios where read access could be escalated to write access through race conditions involving mm/gup.c and mm/huge_memory.c.

Attack Vector

This is a local attack vector requiring an attacker to have local access to the system with low-level privileges. The attack exploits the race condition between permission checks and memory operations. While no user interaction is required, the attack complexity is high due to the precise timing requirements needed to exploit the race condition window successfully. The vulnerability affects both confidentiality and integrity of data, though availability impact is minimal.

The exploitation requires:

1. Local access to a vulnerable Linux system
2. Ability to execute code that interacts with the kernel's memory management
3. Precise timing to hit the race condition window between CoW permission checks and memory access operations

For detailed technical analysis of the vulnerability mechanics, refer to the Chromium Project Zero Issue.

Detection Methods for CVE-2020-29374

Indicators of Compromise

• Unexpected memory page modifications or data corruption in processes utilizing shared memory
• Anomalous memory access patterns involving copy-on-write pages
• Unusual system call sequences targeting get_user_pages functionality
• Process behavior indicating attempts to exploit memory race conditions

Detection Strategies

• Monitor kernel logs for memory management anomalies and unexpected CoW page behavior
• Deploy SentinelOne agents with kernel-level visibility to detect suspicious memory access patterns
• Implement system call auditing for operations that interact with GUP functionality
• Use kernel integrity monitoring tools to detect unauthorized memory modifications

Monitoring Recommendations

• Enable enhanced logging for memory management subsystem events
• Configure SentinelOne's behavioral AI engine to detect exploitation attempts targeting kernel memory functions
• Monitor for processes making repeated attempts to access CoW pages with suspicious timing patterns
• Implement runtime kernel integrity verification to detect successful exploitation

How to Mitigate CVE-2020-29374

Immediate Actions Required

• Update Linux kernel to version 5.7.3 or later immediately
• Apply vendor-specific patches from Debian, NetApp, or other affected distributions
• Review systems running kernel versions prior to 5.7.3 and prioritize patching based on exposure
• Deploy kernel live patches where available to minimize downtime

Patch Information

The vulnerability has been addressed in Linux kernel version 5.7.3. The fix is tracked by commit 17839856fd588f4ab6b789f482ed3ffd7c403e1f in the upstream kernel repository. Organizations should reference the Linux Kernel ChangeLog 5.7.3 for complete details.

Vendor-specific patches are available:

• Debian users should apply updates per Debian Security Advisory DSA-5096
• NetApp users should review NetApp Security Advisory NTAP-20210115-0002
• Kernel live patches are available via Packet Storm Security Notice

Workarounds

• Limit local access to systems running vulnerable kernel versions
• Implement strict user privilege separation to minimize potential attack surface
• Consider containerization with appropriate security profiles to isolate processes
• Monitor and restrict applications that heavily utilize memory pinning or direct memory access operations

# Check current kernel version
uname -r

# Verify if patched version is installed (should be 5.7.3 or later)
dpkg -l linux-image-* 2>/dev/null | grep -E "^ii" | awk '{print $2, $3}'

# For systems using kernel live patching
cat /sys/kernel/livepatch/*/enabled 2>/dev/null