CVE-2026-98091
Summary
by MITRE • 09/25/2026
In the Linux kernel, the following vulnerability has been resolved:
btrfs: detach failed sprout device from transaction update list
When creating the first metadata chunk for a sprout filesystem, create_chunk() adds the new device to the transaction dev_update_list through device->post_commit_list.
If the subsequent system chunk creation fails, btrfs_init_new_device() aborts the transaction and releases the device while post_commit_list is still linked. This triggers a warning in btrfs_free_device() and leaves the transaction list referencing freed memory.
Detach the device while holding chunk_mutex before releasing it.
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Analysis
by VulDB Data Team • 09/25/2026
The vulnerability identified within the Linux kernel's Btrfs filesystem implementation involves a critical use-after-free condition arising from improper resource management during the initialization of sprout devices. A sprout filesystem is a specific configuration in Btrfs where multiple physical devices are combined into a single logical volume, often used to expand existing file systems or create new ones with redundancy. The flaw occurs specifically during the creation phase when the system attempts to allocate the first metadata chunk for this newly formed sprout structure. During this process, the function create_chunk() erroneously adds the new device's data structures to the transaction dev_update_list via the post_commit_list linkage before the entire allocation sequence is fully validated and committed.
The core technical flaw lies in the error handling path when subsequent system chunk creation fails. In such a failure scenario, the kernel invokes btrfs_init_new_device() which triggers an abort of the current transaction. While this function correctly proceeds to release or free the device memory associated with the sprout attempt, it neglects to remove the device from the post_commit_list linkage before doing so. Consequently, the transaction list retains a dangling pointer to memory that has already been freed by the kernel's allocator. This state creates a classic use-after-free vulnerability where subsequent operations on the transaction or related data structures may dereference this invalid pointer, potentially leading to kernel panics, data corruption, or arbitrary code execution if an attacker can influence the allocation patterns and trigger this specific failure path repeatedly.
From a security taxonomy perspective, this issue is classified under CWE-416, which denotes Use After Free vulnerabilities. The improper detachment of the device from the transaction update list means that the kernel maintains references to deallocated memory objects. This aligns with ATT&CK technique T1059, Command and Scripting Interpreter, if an attacker leverages this instability to crash the system for denial-of-service purposes or potentially escalate privileges by exploiting the corrupted memory state during subsequent filesystem operations. The vulnerability highlights a gap in the kernel's transaction management logic where cleanup routines do not adequately synchronize with list manipulation steps under mutex protection.
The operational impact of this vulnerability includes potential stability degradation and security risks to systems utilizing Btrfs sprout configurations. A successful exploitation could result in a system crash, manifesting as a kernel oops or panic, thereby causing a denial of service for all services running on the affected host. Furthermore, because the issue involves memory corruption within critical filesystem structures, it poses a risk to data integrity if the corrupted pointers lead to writes into unintended memory locations during subsequent transaction commits or device management tasks. This is particularly dangerous in production environments where Btrfs sprout setups are used for high-availability storage solutions.
The resolution implemented by the Linux kernel maintainers addresses this flaw by enforcing proper synchronization and cleanup procedures. Specifically, the fix ensures that the failed sprout device is detached from the transaction update list while holding the chunk_mutex before the device memory is released. This change guarantees that no dangling references remain in the active transaction lists when the resource is freed, thereby eliminating the use-after-free condition. To mitigate this vulnerability, system administrators should ensure their Linux kernels are updated to versions containing this patch. Additionally, monitoring kernel logs for warnings related to btrfs_free_device can help identify systems where similar race conditions or memory management errors might be occurring due to older unpatched code paths.