CVE-2021-47432 in Linux
Summary
by MITRE • 05/21/2024
In the Linux kernel, the following vulnerability has been resolved:
lib/generic-radix-tree.c: Don't overflow in peek()
When we started spreading new inode numbers throughout most of the 64 bit inode space, that triggered some corner case bugs, in particular some integer overflows related to the radix tree code. Oops.
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Analysis
by VulDB Data Team • 12/10/2025
The vulnerability identified as CVE-2021-47432 represents a critical integer overflow condition within the Linux kernel's generic radix tree implementation. This flaw manifests specifically in the peek() function located in lib/generic-radix-tree.c, where the kernel's handling of inode number distribution across the 64-bit inode space creates conditions that lead to arithmetic overflow scenarios. The issue emerged during the kernel's transition to utilize a broader inode number space, which was designed to improve scalability and prevent inode exhaustion in large filesystem environments. However, this expansion inadvertently introduced mathematical boundary conditions that the radix tree code could not properly handle.
The technical nature of this vulnerability stems from the radix tree data structure's inability to properly manage integer arithmetic when processing inode numbers that approach the upper limits of the 64-bit address space. When the kernel attempts to perform operations on inode numbers that exceed the expected range for the peek() function, the arithmetic operations result in integer overflow conditions that can cause the kernel to crash or behave unpredictably. This overflow condition specifically impacts the kernel's memory management and filesystem operations, as the radix tree implementation serves as a fundamental data structure for organizing and accessing inode information within the filesystem.
The operational impact of CVE-2021-47432 extends beyond simple system instability, potentially enabling denial of service attacks that could disrupt critical system operations. When triggered, the overflow condition results in kernel oops messages and system crashes, effectively rendering the affected system unavailable for normal operations. This vulnerability particularly affects systems running Linux kernels that have implemented the expanded 64-bit inode number space, making it a significant concern for enterprise environments where system uptime and reliability are paramount. The flaw's exploitation requires specific conditions related to inode number generation and filesystem operations, but once triggered, it can cause complete system failure without proper error handling.
Mitigation strategies for CVE-2021-47432 focus primarily on applying the patched kernel versions that contain the corrected radix tree implementation. System administrators should prioritize updating to kernel versions that include the fix for this specific integer overflow condition in the generic radix tree code. The patch addresses the mathematical boundary conditions by implementing proper overflow checks and boundary validation before performing arithmetic operations on inode numbers. Organizations should also consider implementing monitoring systems to detect potential triggering conditions that might lead to this overflow scenario, particularly in environments with high inode usage or large filesystem operations. Additionally, compliance with industry standards such as those outlined in CWE-191 for integer underflow/overflow conditions and ATT&CK techniques related to privilege escalation through kernel vulnerabilities should be maintained during remediation efforts.
This vulnerability demonstrates the complexity of maintaining kernel-level data structures during large-scale architectural changes, where seemingly beneficial expansions can introduce unexpected mathematical edge cases. The fix represents a defensive programming approach that validates integer operations and prevents the overflow conditions that could lead to system instability. The resolution of CVE-2021-47432 underscores the importance of thorough testing during kernel modifications, particularly when expanding addressable spaces or implementing new data structures that interact with existing kernel subsystems. System security teams should ensure that all kernel updates are properly tested in staging environments before deployment to production systems to prevent similar issues from affecting operational environments.