CVE-2025-38478 in Linux
Summary
by MITRE • 07/28/2025
In the Linux kernel, the following vulnerability has been resolved:
comedi: Fix initialization of data for instructions that write to subdevice
Some Comedi subdevice instruction handlers are known to access instruction data elements beyond the first `insn->n` elements in some cases. The `do_insn_ioctl()` and `do_insnlist_ioctl()` functions allocate at least `MIN_SAMPLES` (16) data elements to deal with this, but they do not initialize all of that. For Comedi instruction codes that write to the subdevice, the first `insn->n` data elements are copied from user-space, but the remaining elements are left uninitialized. That could be a problem if the subdevice instruction handler reads the uninitialized data. Ensure that the first `MIN_SAMPLES` elements are initialized before calling these instruction handlers, filling the uncopied elements with 0. For `do_insnlist_ioctl()`, the same data buffer elements are used for handling a list of instructions, so ensure the first `MIN_SAMPLES` elements are initialized for each instruction that writes to the subdevice.
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Analysis
by VulDB Data Team • 01/25/2026
The vulnerability described in CVE-2025-38478 resides within the Linux kernel's Comedi subsystem, which provides a framework for handling data acquisition and control operations in industrial computing environments. This subsystem interfaces with various hardware devices through subdevice instruction handlers that process input/output operations. The flaw manifests in how the kernel allocates and initializes memory buffers for handling instruction data, creating potential security risks through uninitialized memory access patterns.
The technical root cause involves the improper initialization of data buffers within the `do_insn_ioctl()` and `do_insnlist_ioctl()` functions that manage Comedi instruction processing. These functions allocate memory space sufficient for at least `MIN_SAMPLES` (16) data elements to accommodate potential access patterns beyond the first `insn->n` elements. However, while the first `insn->n` elements receive data copied from user-space, the remaining elements remain uninitialized. This creates a scenario where instruction handlers that write to subdevices may inadvertently read uninitialized memory, potentially exposing sensitive information or creating exploitable conditions.
The operational impact of this vulnerability extends beyond simple information disclosure, as it creates potential attack vectors through uninitialized memory access patterns that could be leveraged for privilege escalation or data corruption. The flaw specifically affects Comedi instruction codes that write to subdevices, making it particularly concerning for industrial control systems and embedded environments where these drivers are commonly deployed. Attackers could potentially exploit this uninitialized memory access to infer system state information or manipulate device behavior through carefully crafted instruction sequences.
The fix implemented addresses the vulnerability by ensuring that all elements within the first `MIN_SAMPLES` buffer are initialized before instruction handlers are invoked, specifically filling uncopied elements with zero values. This approach aligns with secure coding practices and follows the principle of least privilege by preventing access to uninitialized memory regions. The mitigation strategy also extends to the `do_insnlist_ioctl()` function, where the same data buffer elements are utilized for handling multiple instructions, requiring initialization for each instruction that writes to subdevices. This comprehensive fix addresses both single instruction and instruction list processing scenarios, providing robust protection against uninitialized memory access patterns.
This vulnerability demonstrates characteristics consistent with CWE-1286, which addresses improper initialization of data structures, and relates to broader security concerns in kernel space memory management. The issue highlights the importance of proper memory initialization in kernel modules, particularly those handling user-space interactions where data integrity is paramount. From an ATT&CK perspective, this vulnerability could enable privilege escalation techniques through uninitialized memory access patterns, potentially allowing attackers to move laterally within systems or establish persistent access to industrial control environments where Comedi drivers are deployed. The fix represents a fundamental security improvement that aligns with kernel security best practices and reduces the attack surface for industrial control system vulnerabilities.