CVE-2026-90122 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
clk: visconti: Make sure clk_init_data is fully initialized
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.
visconti_clk_register_gate() fills in init.parent_data, and assumes that init.parent_names is NULL. However, the latter in uninitialized, and thus may cause a crash.
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 • 09/17/2026
The Linux kernel clock framework relies on complex data structures to manage hardware clock trees, with clk_init_data serving as a central structure that defines how clocks are configured and connected. This structure contains multiple mutually exclusive members designed to specify possible parent clocks using either string-based names or direct pointer references. The design assumes that driver developers will initialize only the specific fields relevant to their implementation strategy while leaving others in an undefined state, relying on the framework logic to ignore uninitialized branches of the union-like data layout. However, this assumption introduces a significant risk when memory initialization policies change across different kernel configurations or compiler optimizations.
The vulnerability specifically affects the visconti_clk_register_gate function within the Toshiba Visconti clock driver implementation. This routine populates the parent_data member with direct pointer references to parent clocks but incorrectly assumes that the parent_names array remains null due to its own non-initialization of that field. Under standard compilation settings, stack memory often retains zeroed values from previous allocations or kernel initialization routines, masking this defect through coincidence rather than correctness. Consequently, the code appears to function normally in many deployment scenarios despite containing a latent logic error where uninitialized memory is accessed under specific conditions.
The severity and visibility of this flaw are heavily dependent on compiler flags related to stack initialization. When CONFIG_INIT_STACK_ALL_PATTERN is enabled, which fills unused stack space with detectable patterns for debugging purposes, or when CONFIG_INIT_STACK_NONE disables automatic zeroing entirely, the parent_names field may contain arbitrary garbage data from previous function calls. This leads to unpredictable behavior ranging from subtle logical errors in clock tree traversal to immediate kernel panics and system crashes if the framework attempts to dereference invalid pointers derived from these uninitialized values. The issue highlights a critical gap between defensive programming practices and reliance on implicit memory states that are not guaranteed by the C standard or modern compiler behaviors.
From a security perspective, this vulnerability represents an Uninitialized Read classified under CWE-908 in the Common Weakness Enumeration taxonomy. It allows for potential denial of service through kernel crashes when triggered via clock registration paths during system boot or module loading phases. Although it does not directly facilitate privilege escalation without further exploitation chains involving other vulnerabilities, the instability introduced can disrupt critical hardware operations and compromise system reliability. The ATT&CK framework categorizes such issues under techniques related to resource exhaustion or disruption of availability, particularly in environments where kernel stability is paramount for operational continuity.
The resolution involves enforcing strict initialization of all members within the clk_init_data structure regardless of which specific parent specification method is being utilized. By explicitly setting unused fields to null or zero values before passing the structure to the clock framework core, developers eliminate reliance on undefined behavior and ensure consistent operation across different kernel configurations. This approach aligns with secure coding standards that mandate explicit initialization of all variables prior to use, thereby preventing information leaks through uninitialized memory and avoiding crashes caused by garbage data interpretation.
Mitigation strategies for organizations running affected Linux kernels include applying the upstream patch immediately upon availability or backporting the fix if maintaining a specific LTS version is required. Administrators should also consider enabling CONFIG_INIT_STACK_ALL_PATTERN in development environments to proactively detect similar latent bugs across other drivers before they manifest as production incidents. Regular auditing of clock driver implementations against CWE-908 guidelines can help identify and rectify analogous issues throughout the kernel codebase, ensuring robustness against variations in compiler behavior and memory management policies.