CVE-2026-98826 in Linux
Summary
by MITRE • 10/18/2026
In the Linux kernel, the following vulnerability has been resolved:
rtc: ac100: Fix clock provider use-after-free on probe failure
ac100_rtc_register_clks() registers the RTC-32k clock with clk_hw_register_fixed_rate() and the clock provider with of_clk_add_hw_provider(). Neither is device managed, and both are released only from ac100_rtc_remove(). The driver core does not call remove() when probe() fails: really_probe() reaches probe_failed below the device_remove() call and goes straight to releasing the device's managed resources.
ac100_rtc_probe() ends with
return devm_rtc_register_device(chip->rtc);
so if that fails after the clocks have been registered, the provider is left on the global of_clk_providers list holding chip->clk_data, which was allocated with devm_kzalloc() and is freed while probe() unwinds. A later lookup on this device tree node then reads freed memory in of_clk_hw_onecell_get(). Consumers that do exactly that exist in tree: the wifi power sequence nodes on sun8i-a83t-bananapi-m3 and sun8i-a83t-cubietruck-plus take <&ac100_rtc 1>, and the sun9i-a80 boards route osc32k through <&ac100_rtc 0>. The window is narrow, as devm_rtc_register_device() can only fail with -ENOMEM here, but the provider is left dangling whenever it does.
The RTC-32k clock is leaked on the same path. Since clk_core_lookup() searches a global list that is not scoped per device, __clk_register() rejects the duplicate name with -EEXIST, so the leak also makes a later probe of the same device fail.
The error path that returns -EINVAL when the ADDA 4M parent clock cannot be found leaks the RTC-32k clock in the same way. No provider has been registered at that point, so that one is a leak rather than a use-after-free.
Register both with devm_clk_hw_register_fixed_rate() and devm_of_clk_add_hw_provider() so that they are released whenever the device goes away, on a failed probe as well as on unbind. Devres releases in reverse order of acquisition, so the provider is removed before chip->clk_data is freed, and the clkout children are now unregistered before their parent rather than after it. ac100_rtc_unregister_clks() and the remove callback then have nothing left to do and are removed.
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Analysis
by VulDB Data Team • 10/18/2026
The Linux kernel driver for the AC100 real-time clock contains a critical resource management flaw that results in both use-after-free vulnerabilities and memory leaks during probe failure scenarios. This issue stems from the improper handling of clock provider registration within the device initialization sequence. Specifically, the function ac100_rtc_register_clks registers the RTC-32k clock using clk_hw_register_fixed_rate and adds a clock provider via of_clk_add_hw_provider. Neither of these operations utilizes managed resource APIs, meaning they are not automatically cleaned up by the kernel's devres subsystem when device initialization fails. Instead, cleanup is deferred to the ac100_rtc_remove function, which is only invoked if the probe operation completes successfully and subsequently triggers an unbind or removal event.
The vulnerability manifests because the driver core does not call remove() if probe() fails. When really_probe encounters a failure after device resources have been allocated but before initialization is complete, it bypasses the remove callback and proceeds directly to releasing managed resources via devm_kzalloc. In this specific case, while chip->clk_data is correctly freed by the managed resource framework, the global clock provider list retains a reference to that now-freed memory structure. This creates a dangling pointer situation where subsequent lookups on the device tree node can trigger reads from freed memory in of_clk_hw_onecell_get. Although the window for exploitation is narrow because devm_rtc_register_device typically only fails with -ENOMEM, the presence of consumers such as wifi power sequence nodes on sun8i-a83t-bananapi-m3 and sun8i-a83t-cubietruck-plus that reference <&ac100_rtc 1>, or sun9i-a80 boards routing osc32k through <&ac100_rtc 0>, means these dangling pointers can be dereferenced, leading to potential kernel crashes or undefined behavior.
Beyond the use-after-free condition, the same code path also introduces a resource leak that causes secondary failures. The RTC-32k clock is registered globally but not freed upon probe failure because the cleanup logic in ac100_rtc_remove is skipped. Since clk_core_lookup searches a global list scoped per device name rather than per instance, any subsequent attempt to probe the same device will encounter -EEXIST due to the duplicate registration of the RTC-32k clock. This effectively bricks the driver for future initialization attempts on that hardware until a reboot occurs. Additionally, an error path returning -EINVAL when the ADDA 4M parent clock is missing leaks the RTC-32k clock without registering a provider, resulting in a pure memory leak rather than a use-after-free vulnerability.
The resolution involves refactoring the driver to utilize managed resource APIs for all clock-related operations. By replacing clk_hw_register_fixed_rate with devm_clk_hw_register_fixed_rate and of_clk_add_hw_provider with devm_of_clk_add_hw_provider, the kernel ensures that these resources are automatically released whenever the device goes away, regardless of whether it is due to successful unbind or probe failure. The devres framework releases managed resources in reverse order of acquisition, guaranteeing that the clock provider is removed from the global list before chip->clk_data is freed. This ordering prevents dangling pointers and ensures that clkout children are unregistered before their parent. Consequently, the manual cleanup functions ac100_rtc_unregister_clks and the remove callback become redundant and can be safely removed, simplifying the driver code while eliminating both security vulnerabilities and resource leaks.
This vulnerability aligns with CWE-416 Use After Free, as it involves accessing memory that has already been freed due to improper lifecycle management of kernel objects. It also relates to CWE-772 Missing Release of Resource after Effective Lifetime, specifically regarding the failure to release allocated resources when an error occurs during initialization. From a threat modeling perspective using MITRE ATT&CK for ICS or Enterprise frameworks, this represents a potential Denial of Service vector through resource exhaustion or system instability caused by memory corruption. The fix ensures robustness against probe failures and maintains kernel integrity by adhering to standard devres patterns that are widely adopted across the Linux kernel subsystems to prevent such lifecycle mismatches.