CVE-2026-98161 in Linux
Summary
by MITRE • 09/25/2026
In the Linux kernel, the following vulnerability has been resolved:
nvdimm: pmem: keep PREFLUSH before data writes
pmem_submit_bio() records a REQ_PREFLUSH error, but continues to copy the bio data and can later overwrite the error with a successful REQ_FUA flush. That lets data writes run after a failed preflush and can complete the bio successfully despite the failed ordering barrier.
Run the REQ_PREFLUSH flush synchronously before touching the bio data and complete the bio with the flush error if it fails. Keep asynchronous flush chaining for REQ_FUA. At that point, data copy has completed and the parent bio can wait for the chained flush bio.
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Analysis
by VulDB Data Team • 09/25/2026
The vulnerability identified in the Linux kernel's persistent memory subsystem involves a critical race condition within the pmem_submit_bio function, which is responsible for handling block I/O requests directed at NVDIMM devices. This flaw specifically affects how write operations are ordered and flushed to ensure data persistence across power failures or system crashes. The core issue arises from an incorrect sequence of operations where the kernel records a failure during the required pre-flush operation but proceeds to copy bio data anyway, potentially overwriting the error status with a successful completion flag after executing a subsequent flush command. This behavior violates fundamental storage integrity principles by allowing data writes to proceed even when the necessary ordering barrier has failed, thereby compromising the reliability of persistent memory operations.
From a technical perspective, the defect lies in the handling of REQ_PREFLUSH and REQ_FUA flags within the block layer's interaction with NVDIMM hardware. When a write request requires strict durability guarantees, it typically involves two steps: first flushing any existing dirty data from caches to ensure order, and then writing new data followed by another flush if required. In this vulnerable implementation, if the initial pre-flush operation fails due to hardware errors or timeouts, the kernel incorrectly continues with copying the bio data into memory buffers. Subsequently, when a REQ_FUA (Force Unit Access) flush is executed asynchronously, it may succeed even though the preceding critical ordering step failed. The code then marks the entire bio as successfully completed, effectively hiding the initial failure and allowing potentially inconsistent or lost data to be committed without proper error propagation to the upper layers of the storage stack.
The operational impact of this vulnerability is severe for systems relying on persistent memory for mission-critical applications such as databases, financial transaction processing, or real-time analytics where data consistency is paramount. By allowing writes to complete successfully despite a failed pre-flush, the system risks silent data corruption or loss in scenarios involving unexpected power cycles or hardware resets. Applications expecting atomicity and durability guarantees may proceed under the false assumption that their data has been safely persisted, leading to potential financial losses, regulatory non-compliance, or application crashes upon recovery from such events. This undermines trust in the storage subsystem and can lead to significant operational disruptions requiring complex forensic analysis to determine which data was affected.
This issue aligns with CWE-362, Concurrent Execution using Shared Resource with Improper Synchronization of Accessed Resources, as it involves improper handling of asynchronous operations where state is not correctly maintained across dependent steps. It also relates to CWE-754, Improper Check for Unusual or Exceptional Conditions, because the code fails to properly validate and propagate error states from critical initialization phases before proceeding with subsequent actions. In terms of MITRE ATT&CK techniques, while this is primarily a reliability issue rather than an exploit vector, it could be leveraged in advanced persistent threat scenarios where attackers might induce storage errors to cause denial of service or data corruption for specific targets, mapping loosely to T1485 Data Destruction if the resulting inconsistency leads to irreversible loss.
To mitigate this vulnerability and restore correct behavior, the kernel must enforce synchronous execution of REQ_PREFLUSH operations before any bio data is copied or processed further. If a pre-flush fails, the error should be immediately propagated up the stack without proceeding with subsequent write steps that depend on successful completion of prior ordering barriers. For requests requiring both flush and write semantics via REQ_FUA, asynchronous chaining remains acceptable provided that the parent bio correctly waits for the chained flush bio to complete before marking itself as done. This ensures that all durability guarantees are honored in sequence and that any failures at earlier stages prevent subsequent operations from masking those errors. System administrators should ensure their kernels are updated with patches addressing this specific logic error in pmem_submit_bio, particularly on systems utilizing NVDIMM hardware for persistent storage workloads requiring high availability and data integrity standards compliant with industry best practices such as POSIX fsync semantics or database ACID properties.