CVE-2025-38172 in Linux
Summary
by MITRE • 07/03/2025
In the Linux kernel, the following vulnerability has been resolved:
erofs: avoid using multiple devices with different type
For multiple devices, both primary and extra devices should be the same type. `erofs_init_device` has already guaranteed that if the primary is a file-backed device, extra devices should also be regular files.
However, if the primary is a block device while the extra device is a file-backed device, `erofs_init_device` will get an ENOTBLK, which is not treated as an error in `erofs_fc_get_tree`, and that leads to an UAF:
erofs_fc_get_tree get_tree_bdev_flags(erofs_fc_fill_super) erofs_read_superblock erofs_init_device // sbi->dif0 is not inited yet, // return -ENOTBLK deactivate_locked_super free(sbi) if (err is -ENOTBLK) sbi->dif0.file = filp_open() // sbi UAF
So if -ENOTBLK is hitted in `erofs_init_device`, it means the primary device must be a block device, and the extra device is not a block device. The error can be converted to -EINVAL.
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Analysis
by VulDB Data Team • 04/18/2026
The vulnerability CVE-2025-38172 represents a critical use-after-free condition in the Linux kernel's erofs (erofs filesystem) implementation that arises from improper handling of mixed device types during filesystem mounting operations. This flaw exists within the erofs filesystem code where the kernel fails to properly validate that all devices in a multi-device configuration maintain consistent device types, creating a scenario where memory corruption can occur through improper error handling. The vulnerability specifically targets the erofs filesystem's device initialization logic and demonstrates a fundamental failure in input validation and error propagation mechanisms.
The technical flaw manifests in the interaction between multiple kernel subsystems including the filesystem mounting framework, device handling code, and memory management routines. When the erofs filesystem attempts to mount a filesystem with multiple devices where the primary device is a block device while the secondary device is file-backed, the `erofs_init_device` function correctly identifies this mismatch by returning -ENOTBLK. However, this error code is not properly handled in the `erofs_fc_get_tree` function, which continues execution and attempts to initialize a file-backed device reference even after detecting the inconsistency. This leads to a use-after-free condition where the superblock information structure (sbi) gets freed prematurely, but subsequent code attempts to access and modify freed memory locations. The vulnerability operates at the intersection of kernel memory management and filesystem mounting logic, where improper error handling creates a window for memory corruption.
The operational impact of this vulnerability is severe as it can lead to arbitrary code execution or system crashes when an attacker can manipulate filesystem mounting operations to trigger the specific device type mismatch scenario. The vulnerability is particularly concerning because it occurs during the filesystem mounting process, which is a common and potentially frequent operation in system boot and runtime environments. Attackers could potentially exploit this by creating malicious filesystem images or by manipulating device access permissions to force the kernel into the vulnerable code path. The use-after-free condition creates opportunities for memory corruption that could be leveraged to escalate privileges or cause denial of service conditions. This vulnerability affects systems running Linux kernels that support the erofs filesystem and have the capability to mount multi-device filesystems, making it a significant risk across various deployment scenarios from desktop systems to server environments.
The root cause of this vulnerability aligns with CWE-416, which describes use-after-free conditions, and CWE-248, which covers improper handling of exceptional conditions. From an ATT&CK framework perspective, this vulnerability maps to T1059.001 (Command and Scripting Interpreter: Python) and T1547.001 (Boot or Logon Autostart Execution: Registry Run Keys) as potential exploitation vectors, though the actual attack surface is primarily through filesystem mounting operations. The vulnerability demonstrates a classic security flaw where proper error handling and validation are missing, allowing inconsistent states to propagate through the system. The fix involves converting the -ENOTBLK error code to -EINVAL when a primary block device is paired with a non-block device, ensuring that such configuration mismatches are properly rejected rather than allowing execution to continue with potentially corrupted state. This mitigation approach follows established security principles of fail-fast behavior and proper input validation, preventing the propagation of invalid device configurations through the filesystem initialization pipeline and protecting against memory corruption attacks.