CVE-2026-98667 in Linux
Summary
by MITRE • 10/18/2026
In the Linux kernel, the following vulnerability has been resolved:
iio: frequency: adf4377: Fully initialize clk_init_data and clk_parent_data
The clk_init_data structure contains several mutually-exclusive members for different methods to specify the possible parents of a clock, prompting drivers to initialize only the members they need. However, not initializing all members may cause subtle issues, which are only exposed when CONFIG_INIT_STACK_ALL_PATTERN or CONFIG_INIT_STACK_NONE is enabled.
adf4377_clk_register() fills in init.parent_data, and assumes that init.parent_names is NULL. However, the latter is uninitialized, and thus may cause a crash.
Similarly, adf4377_clk_register() fills in only parent_data.fw_name, leaving other members of the clk_parent_data structure uninitialized.
Make sure all members are fully initialized, to fix such bugs, and to avoid future breakage when converting drivers to a different method for specifying the parents.
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Analysis
by VulDB Data Team • 10/18/2026
The Linux kernel's Industrial I/O subsystem contains a driver for the ADF4377 frequency synthesizer that exhibits improper memory initialization practices within its clock registration logic. This vulnerability stems from the handling of two critical data structures: clk_init_data and clk_parent_data. These structures are designed to support multiple mutually exclusive methods for specifying clock parents, allowing drivers flexibility in how they define parent clocks. However, this design requires strict discipline in zeroing out unused fields before populating only the relevant ones. The adf4377_clk_register function fails to adhere to this requirement by partially initializing these structures without ensuring that all members are explicitly set or cleared beforehand. This oversight leads to undefined behavior when the kernel's stack initialization configurations interact with the driver, potentially resulting in system instability or crashes.
The technical flaw is most pronounced under specific kernel configuration settings involving stack initialization policies such as CONFIG_INIT_STACK_ALL_PATTERN and CONFIG_INIT_STACK_NONE. When these options are enabled, they alter how memory on the call stack is populated before function execution. In a standard scenario where stack memory might coincidentally contain zeros, the uninitialized fields in clk_init_data and clk_parent_data may appear harmless. However, under configurations that do not guarantee zeroed stacks or use specific patterns for debugging, these uninitialized members retain garbage values from previous stack usage. Specifically, adf4377_clk_register populates init.parent_data but assumes that init.parent_names remains NULL. Because parent_names is never explicitly initialized to NULL, it may contain a non-null pointer value pointing to invalid memory. This discrepancy causes the clock framework to misinterpret the data structure, leading to dereferencing of invalid pointers and subsequent kernel panics or crashes during device initialization or operation.
Furthermore, within the clk_parent_data structure, the driver only initializes the fw_name member while leaving other fields in that struct uninitialized. Similar to the parent_names issue, these leftover values can cause confusion for the clock framework's internal logic which expects consistent state across all members of the union-like structures used for specifying parents. This lack of comprehensive initialization violates fundamental principles of safe C programming within kernel space and represents a classic instance of improper input validation or state management where assumptions about memory content are made without verification. The vulnerability is categorized under CWE-457, which describes the use of an uninitialized variable, as well as CWE-908 regarding the use of hardcoded resource identifiers that may lead to unintended behavior if not properly scoped and initialized.
The operational impact of this vulnerability includes potential denial of service through kernel crashes when devices using the ADF437 driver are probed or configured on systems with specific stack initialization configurations enabled for debugging or security hardening purposes. While exploitation by an external attacker is unlikely due to the local nature of device probing and the requirement for physical access or privileged user context to load such drivers, the instability poses a significant risk to system reliability. It can lead to unexpected reboots or service interruptions in embedded systems relying on this hardware component. The issue highlights the fragility of driver code that relies on implicit memory states rather than explicit initialization, which becomes increasingly problematic as kernel security features evolve to detect and prevent such ambiguities.
To mitigate this vulnerability, developers must ensure that all members of clk_init_data and clk_parent_data are fully initialized before use. This involves explicitly setting unused fields to NULL or zero values prior to populating the specific fields required by the driver logic. The fix entails modifying adf4377_clk_register to perform a complete initialization of these structures, thereby eliminating reliance on stack content assumptions. From an architectural perspective, this aligns with best practices recommended in ATT&CK technique T1059 regarding command and script interpretation, where ensuring proper state management prevents unintended execution paths. System administrators should apply the patched kernel version which includes corrections to fully initialize these data structures, ensuring that future conversions or updates to clock specification methods do not reintroduce similar flaws. Regular code audits focusing on memory initialization in hardware drivers are essential to maintain robustness against such subtle but critical defects.