CVE-2022-50746 in Linux
Summary
by MITRE • 12/24/2025
In the Linux kernel, the following vulnerability has been resolved:
erofs: validate the extent length for uncompressed pclusters
syzkaller reported a KASAN use-after-free: https://syzkaller.appspot.com/bug?extid=2ae90e873e97f1faf6f2
The referenced fuzzed image actually has two issues: - m_pa == 0 as a non-inlined pcluster; - The logical length is longer than its physical length.
The first issue has already been addressed. This patch addresses the second issue by checking the extent length validity.
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Analysis
by VulDB Data Team • 04/21/2026
The vulnerability CVE-2022-50746 affects the Linux kernel's erofs (Erofs: Enhanced Read-Only File System) implementation and represents a critical validation flaw in the handling of uncompressed pclusters. This issue was discovered through systematic fuzzing operations conducted by the syzkaller project, which identified a kernel address sanitizer (KASAN) use-after-free condition during file system operations. The reported bug demonstrates how malformed file system images can trigger memory safety violations in kernel space, highlighting the importance of robust input validation in kernel-level file system drivers.
The technical flaw manifests in the validation of extent lengths for uncompressed pclusters within the erofs implementation. When processing fuzzed file system images, the kernel encounters cases where the logical length of data exceeds its physical length, creating an inconsistency that can lead to memory corruption. The vulnerability specifically targets the pcluster (physical cluster) handling logic where uncompressed data structures are processed without proper validation of their extent boundaries. This validation failure occurs during the processing of file system metadata where the kernel fails to verify that logical extent lengths do not exceed physical storage capacity, creating potential for memory access violations.
The operational impact of this vulnerability extends beyond simple memory corruption, as it represents a potential vector for privilege escalation or denial of service attacks within kernel space. When the erofs file system attempts to process malformed images containing extended logical lengths that exceed physical storage limits, the kernel's memory management can become corrupted, potentially allowing attackers to execute arbitrary code with kernel privileges. The vulnerability affects systems running Linux kernels that support the erofs file system, particularly those utilizing compressed file systems where pcluster handling is critical for performance optimization. This flaw demonstrates the broader category of software defects classified under CWE-129 Input Validation and CWE-787 Out-of-bounds Write, which are fundamental security concerns in kernel development.
The patch addressing CVE-2022-50746 implements additional validation checks for extent length validity, ensuring that logical extent lengths never exceed their corresponding physical storage limits. This mitigation directly addresses the second issue identified in the fuzzed image where m_pa == 0 was already resolved, but the logical-to-physical length relationship remained unchecked. The fix follows established security practices for kernel development, implementing defensive programming techniques that align with the ATT&CK framework's concept of privilege escalation through kernel vulnerabilities. By enforcing proper extent length validation, the patch prevents the use-after-free conditions that could be exploited to gain unauthorized access to kernel memory spaces and potentially compromise the entire system integrity.
The broader implications of this vulnerability highlight the critical importance of input validation in kernel-level code, particularly for file system implementations that handle untrusted data from external sources. The issue demonstrates how fuzzing tools like syzkaller can identify subtle memory safety violations that might otherwise remain undetected in normal operation. The vulnerability also underscores the need for comprehensive testing of edge cases in kernel code, as the malformed file system images that triggered this issue represent real-world scenarios where attackers might attempt to exploit similar validation flaws in other kernel subsystems. This particular case reinforces the principle that kernel security requires rigorous validation of all input parameters, especially in performance-critical components where optimization might inadvertently introduce security weaknesses.