CVE-2026-68416 in Linux
Summary
by MITRE • 08/10/2026
In the Linux kernel, the following vulnerability has been resolved:
mtd: fix double free and WARN_ON in add_mtd_device() error paths
When device_register() or mtd_nvmem_add() fails inside add_mtd_device() for a partition, the error handling triggers mtd_release() via put_device() or device_unregister(). mtd_release() calls release_mtd_partition() which frees the mtd_info structure. However, callers such as mtd_add_partition() and add_mtd_partitions() also call free_partition() in their error paths, resulting in a double free.
Additionally, release_mtd_partition() hits WARN_ON(!list_empty( &mtd->part.node)) because the partition node is still linked in the parent's partitions list when the release callback fires from the add_mtd_device() error path.
Fix this by overriding dev->type and dev->release before put_device() in the error paths, so that device_release() invokes a no-op function instead of mtd_release(). For the mtd_nvmem_add() failure case, device_unregister() is replaced with device_del() to separate the device removal from the final kobject reference drop, allowing the override to take effect before put_device() is called.
The callers' error paths (list_del + free_partition) remain the sole owners of mtd_info lifetime on add_mtd_device() failure, which is the expected contract.
The normal partition teardown path is not affected: del_mtd_device() goes through kref_put() -> mtd_device_release() -> device_unregister() with dev->type still set to &mtd_devtype, so mtd_release() -> release_mtd_partition() continues to work correctly for the regular removal case.
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Analysis
by VulDB Data Team • 08/10/2026
The vulnerability described represents a critical double free condition within the Linux kernel's MTD (Memory Technology Device) subsystem that arises during error handling in the add_mtd_device() function. This flaw occurs when device registration or NVMEM integration fails, creating a scenario where memory management becomes corrupted through improper resource cleanup sequences. The issue manifests as a classic heap corruption vulnerability that could potentially lead to system instability or privilege escalation opportunities.
The technical root cause stems from improper error path handling in the MTD subsystem's device management logic. When device_register() or mtd_nvmem_add() fails within add_mtd_device(), the error handling code invokes put_device() or device_unregister() which triggers the device release callback mechanism. The standard release function mtd_release() calls release_mtd_partition() which frees the mtd_info structure, but this occurs alongside direct memory cleanup from caller functions like mtd_add_partition() and add_mtd_partitions() that also invoke free_partition() in their error handling sequences. This dual cleanup approach results in a double free condition that violates fundamental memory safety principles.
This vulnerability directly relates to CWE-415, which describes double free conditions in software systems, and represents a classic example of improper resource management in kernel space code. The specific implementation flaw occurs because the device release callback mechanism operates without proper context awareness regarding whether the device object has already been partially cleaned up by error handling paths. The system exhibits WARN_ON behavior due to partition nodes remaining linked in parent device lists when the release callback executes, indicating that the object lifecycle management has become inconsistent.
The proposed fix implements a sophisticated device type override mechanism that prevents the problematic mtd_release() callback from executing during error paths while maintaining normal operation for legitimate device removal scenarios. By overriding dev->type and dev->release before put_device() calls in error conditions, the system ensures that device_release() invokes no-op functions instead of triggering the memory freeing logic. For the mtd_nvmem_add() failure case, replacing device_unregister() with device_del() provides the necessary temporal separation to allow the type override to take effect before final reference dropping occurs.
This solution aligns with established kernel development practices for managing complex object lifecycles in error conditions and maintains backward compatibility with existing code paths. The fix preserves the normal partition teardown path through del_mtd_device() which correctly follows kref_put() -> mtd_device_release() -> device_unregister() sequences with dev->type still set to &mtd_devtype, ensuring that legitimate removal cases continue to work properly. The approach demonstrates proper adherence to kernel memory management principles while addressing the specific double free vulnerability without disrupting core functionality.
The operational impact of this vulnerability extends beyond simple memory corruption, as it could potentially enable privilege escalation or system crashes in embedded systems where MTD devices are frequently managed. Attackers could exploit this condition by triggering device registration failures in controlled scenarios, potentially leading to denial of service or unauthorized access to kernel memory spaces. The fix addresses this through careful management of object lifecycle transitions and ensures that resource ownership semantics remain consistent throughout all execution paths.
This vulnerability highlights the complexity inherent in kernel device management systems where multiple code paths must coordinate properly for safe resource handling. The solution demonstrates advanced understanding of Linux kernel object model interactions and proper error path design principles that are essential for maintaining system integrity in production environments. The implementation follows established security practices and maintains compatibility with existing MTD subsystem functionality while resolving the identified double free condition through targeted modifications to device release callback behavior during error scenarios.