CVE-2026-90020 in Linux
Summary
by MITRE • 09/16/2026
In the Linux kernel, the following vulnerability has been resolved:
USB: gadget: fix NULL pointer dereference in gadget_dev_ioctl()
gadget_dev_ioctl() reads dev->gadget before acquiring dev->lock, but dev->state is checked after acquiring the lock. Therefore a concurrent bind can change the device state between these operations, which can leave ioctl with a stale NULL gadget pointer and causing a NULL pointer dereference at gadget->ops->ioctl.
Read dev->gadget while holding dev->lock so that the gadget pointer and device state are sampled consistently.
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Analysis
by VulDB Data Team • 09/16/2026
The Linux kernel USB gadget subsystem contains a concurrency flaw within the gadget_dev_ioctl function, specifically involving improper synchronization of shared data structures during ioctl operations. This vulnerability arises from a race condition where the code attempts to access dev->gadget before acquiring the necessary mutex lock, dev->lock. In concurrent execution environments, particularly when device binding or unbinding occurs simultaneously with an ioctl request, this ordering violation creates a window for state inconsistency. The function checks the device state after locking but retrieves the gadget pointer prior to doing so, meaning the two operations are not atomic relative to each other. This lack of mutual exclusion allows another thread modifying the device configuration to alter dev->state and nullify or change dev->gadget between the initial read and the subsequent lock acquisition.
The operational impact of this race condition is a NULL pointer dereference that can lead to kernel panic, system instability, or denial of service for local users who have access to USB gadget interfaces. When a concurrent bind operation changes the device state while ioctl is in progress, the previously cached reference to dev->gadget may become stale and point to freed memory or remain null if the gadget was unbound during that interval. Subsequently, when the code attempts to invoke operations via gadget->ops->ioctl, it dereferences this invalid pointer, triggering a critical fault within the kernel space. This type of vulnerability is particularly dangerous because USB gadgets often represent interfaces exposed to user-space applications, potentially allowing any local process with appropriate permissions to trigger the condition through standard system calls.
From a classification perspective, this issue aligns with CWE-362, which describes concurrent execution using shared resources with improper synchronization. The root cause lies in the failure to maintain consistent snapshots of related state variables under a single lock scope. Furthermore, from an adversary behavior standpoint, exploiting such race conditions can be categorized under ATT&CK technique T1059, Command and Scripting Interpreter, if leveraged for further exploitation, though primarily it represents a stability issue exploitable via local privilege escalation or denial-of-service vectors depending on the specific kernel configuration and context. The vulnerability highlights the importance of atomicity in multi-threaded kernel subsystems where state transitions must be strictly serialized to prevent data corruption or invalid memory access.
The resolution involves restructuring the code within gadget_dev_ioctl to ensure that dev->gadget is read only after acquiring dev->lock. By sampling both the gadget pointer and the device state while holding the lock, the function guarantees consistency between these two values. This change eliminates the race window where a concurrent bind operation could invalidate the gadget reference before it is used. Implementing this fix ensures that any subsequent operations on the gadget object are performed against a valid, current, and safely referenced structure. Developers should verify that all similar patterns in the USB subsystem adhere to strict lock ordering protocols to prevent analogous issues elsewhere in the codebase. Regular static analysis tools focused on concurrency bugs can help identify such synchronization errors early in the development lifecycle, reducing the attack surface for kernel-level exploits.