CVE-2026-90421 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
PCI: Fix UAF when probe runs concurrent to dyn ID removal
Dynamic IDs are only guaranteed to be valid when dynids.lock is held, as remove_id_store() can free the node. Thus, make a copy in pci_match_device(). Also, clarify that the id parameter is only valid during probe.
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Analysis
by VulDB Data Team • 09/17/2026
The Linux kernel contains a critical use-after-free vulnerability within the Peripheral Component Interconnect subsystem, specifically affecting the device probing mechanism when dynamic identifier management occurs concurrently with driver attachment operations. This flaw arises from an improper handling of memory lifecycles for dynamically allocated PCI device identifiers. The core issue lies in the fact that dynamic IDs are only guaranteed to remain valid and accessible while the dynids.lock is actively held by a thread. However, during the concurrent execution of probe routines and identifier removal processes, this lock may not be consistently maintained or released at appropriate intervals, creating a race condition window where memory can be freed before it is no longer referenced.
The technical root cause involves the remove_id_store function, which is responsible for removing specific dynamic identifiers from PCI device structures. When this function executes, it frees the associated node containing identifier data without ensuring that all concurrent operations accessing these identifiers have completed their read cycles. Specifically, the pci_match_device function, which determines whether a driver matches a given hardware device by comparing its ID against available entries, accesses these dynamically allocated nodes directly. If remove_id_store is executed concurrently and releases memory while pci_match_device is still reading from it, the kernel attempts to dereference freed memory. This constitutes a classic use-after-free vulnerability that can lead to unpredictable system behavior, including kernel panics, data corruption, or potential privilege escalation if an attacker can manipulate timing conditions to exploit this race condition effectively.
The operational impact of this vulnerability extends beyond simple stability issues. A successful exploitation could allow local attackers with sufficient privileges to crash the entire operating system by triggering a null pointer dereference or general protection fault within kernel space. Furthermore, depending on the specific memory allocator state and heap layout at the time of exploitation, an attacker might be able to achieve arbitrary code execution by controlling what data is written into the freed memory region before it is reallocated for another purpose. This represents a significant security risk in environments where PCI devices are frequently added or removed dynamically, such as virtualized cloud infrastructure or systems with hot-pluggable hardware components.
To mitigate this vulnerability, developers have implemented a fix that involves making a local copy of the identifier data within pci_match_device before performing any comparisons against device capabilities. By copying the necessary information while holding the appropriate lock and then releasing it immediately after the copy is complete, the function ensures that subsequent access to the copied data does not depend on the continued validity of the original dynamic node structure. This approach decouples the reading process from the lifetime management of the source object, effectively eliminating the race condition window. Additionally, code comments have been updated to clarify that the id parameter passed during probe operations is only valid for the duration of the probing phase, reinforcing proper usage patterns among kernel developers and reducing future risk of similar errors.
From a standards perspective, this vulnerability aligns with CWE-416, Use After Free, which describes situations where software continues to use memory after it has been freed, leading to undefined behavior. The attack vector relates closely to ATT&CK technique T1059, Command and Scripting Interpreter, as exploitation often requires precise timing control that may be facilitated through scriptable interactions with device management interfaces or automated testing frameworks designed to stress-test hardware enumeration processes. Organizations running affected kernel versions should apply the latest security patches immediately to close this gap in memory safety enforcement within the PCI subsystem. Regular updates ensure that concurrent access patterns are handled according to modern concurrency best practices, preventing potential exploitation of race conditions inherent in dynamic resource management systems.