CVE-2026-98218 in Linux
Summary
by MITRE • 10/06/2026
In the Linux kernel, the following vulnerability has been resolved:
i2c: atr: fix dangling adapter pointer on add failure
i2c_atr_add_adapter() stores atr->adapter[chan_id] before
i2c_add_adapter() so that the I2C bus notifier can match child clients during registration. On failure the channel is freed but the slot was left pointing at freed memory, which can lead to use-after-free in i2c_atr_del_adapter() / cleanup and also block reuse with -EEXIST.
Clear the slot on the i2c_add_adapter() error path before freeing chan.
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Analysis
by VulDB Data Team • 10/06/2026
The Linux kernel's I2C adapter translation (ATR) subsystem contains a critical memory management flaw within its device registration logic, specifically in the function responsible for adding new adapters to the system bus topology. This vulnerability arises from an improper handling of resource cleanup during error conditions, leading to dangling pointers that compromise both system stability and security integrity. The core issue is rooted in the sequence of operations performed when initializing a new I2C channel adapter. To facilitate proper device discovery, the kernel stores a reference to the newly created adapter structure within a global array before completing the full registration process with the I2C bus subsystem via i2c_add_adapter(). This design choice allows the I2C bus notifier mechanism to correctly identify and match child clients during the dynamic registration phase. However, this optimization introduces a significant risk if the subsequent registration step fails for any reason, such as resource exhaustion or hardware configuration errors.
When i2c_add_adapter() returns an error code, indicating that the adapter was not successfully registered with the bus subsystem, the current implementation proceeds to free the memory associated with the channel structure. Crucially, it neglects to clear the pointer stored in the atr->adapter[chan_id] array slot before performing this deallocation. As a result, the system retains a dangling reference to memory that has already been returned to the kernel's allocator pool and is potentially subject to reallocation for other purposes. This creates a classic use-after-free vulnerability scenario where subsequent operations may inadvertently access or modify freed memory, leading to undefined behavior, data corruption, or potential privilege escalation if an attacker can control the contents of the reclaimed memory block.
The operational impact of this flaw extends beyond immediate crashes or kernel panics. The presence of stale pointers in the adapter array prevents the proper reuse of channel identifiers. Specifically, any attempt to add a new adapter using the same channel ID will fail with an -EEXIST error because the system incorrectly perceives that a valid adapter is already present at that index, even though it was never successfully registered and its memory has been freed. This leads to resource leaks in terms of functional capacity, effectively reducing the number of usable I2C channels over time as administrators or automated systems attempt to reconfigure hardware interfaces. Furthermore, if another subsystem allocates new data into the same memory address previously occupied by the adapter structure, accessing this dangling pointer could allow an attacker to read sensitive kernel information or write arbitrary values to critical kernel structures, thereby bypassing standard security controls and compromising system integrity.
From a vulnerability classification perspective, this issue aligns with CWE-416, Use After Free, as it involves referencing memory after it has been freed. It also relates to CWE-825, Expired Pointer Dereference, because the pointer remains valid in terms of address space but points to invalid or unowned data. In the context of the MITRE ATT&CK framework for enterprise security, this type of flaw is relevant to techniques involving memory corruption and exploitation of kernel-level vulnerabilities, which are often leveraged in lateral movement or privilege escalation attacks within compromised environments. The lack of proper pointer nullification represents a fundamental failure in defensive programming practices regarding resource lifecycle management.
To mitigate this vulnerability, the Linux kernel developers have implemented a fix that ensures the adapter slot is explicitly cleared before freeing the channel structure on error paths. This simple but critical change guarantees that no dangling references remain in the global array, thereby preventing use-after-free conditions and allowing for correct reuse of channel identifiers upon retry or reconfiguration. System administrators should ensure their kernels are updated to include this patch, which addresses the root cause by enforcing strict memory safety protocols during device initialization failures. Regular kernel updates and adherence to secure coding standards that mandate nullifying pointers after deallocation are essential practices to prevent similar vulnerabilities in complex subsystems like I2C where dynamic resource allocation is frequent and error handling must be exhaustive.