CVE-2026-98962 in Linux
Summary
by MITRE • 10/23/2026
In the Linux kernel, the following vulnerability has been resolved:
btrfs: free iov when btrfs_uring_read_extent() fails
After btrfs_uring_read_extent(), the caller always jumped to out_acct. That skips kfree(data->iov), which is only correct for -EIOCBQUEUED where the deferred path owns the iov. On failure, fall through to out_free instead.
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Analysis
by VulDB Data Team • 10/23/2026
The identified vulnerability resides within the btrfs filesystem implementation in the Linux kernel, specifically affecting the direct I/O handling mechanism via io_uring. The core issue is a memory management error characterized by an improper release of resources during specific execution paths. When the function btrfs_uring_read_extent encounters a failure condition that does not result in the deferred completion state represented by -EIOCBQUEUED, the control flow incorrectly jumps to the out_acct label. This jump bypasses the necessary cleanup routine responsible for freeing the input/output vector structure allocated as data->iov. Consequently, this logic flaw results in a memory leak where kernel heap memory remains allocated but unreachable after the operation concludes unsuccessfully.
From a technical perspective, this is classified under CWE-401 which denotes missing release of memory after effective usage. The distinction between successful deferred operations and immediate failures was not properly handled by the conditional branching logic. In scenarios where btrfs_uring_read_extent returns -EIOCBQUEUED, it indicates that the I/O operation has been queued for asynchronous completion, meaning another part of the kernel subsystem will eventually handle the cleanup of associated resources. However, in all other failure cases, such as input validation errors or internal filesystem inconsistencies, the responsibility for freeing the allocated buffer lies with the current function context. By skipping this deallocation step, the system accumulates unreleased memory blocks over time during repeated failed operations.
The operational impact of this vulnerability is primarily related to resource exhaustion and potential denial of service conditions within the kernel space. Although individual leaks may appear small depending on the size of the io vector structures involved, sustained exploitation through rapid successive calls can lead to significant degradation in system performance due to increased memory pressure. In extreme cases where available physical memory becomes critically low, this could trigger out-of-memory killer events or cause instability for other running processes sharing the same kernel resources. While direct remote code execution is not implied by this specific flaw, the accumulation of leaked kernel memory reduces the overall resilience and stability of the operating system environment hosting btrfs volumes.
Mitigation strategies involve applying vendor-provided patches that correct the control flow logic to ensure fall-through behavior toward out_free on non-deferred failure paths. Administrators should verify their systems are running updated kernel versions where this specific branch condition has been rectified. Additionally, employing memory debugging tools such as KASAN during development or testing phases can help identify similar resource management oversights in other parts of the filesystem driver before they reach production environments. Regular auditing of kernel logs for signs of excessive memory allocation without corresponding deallocation events serves as a practical monitoring approach to detect potential leaks early.