CVE-2026-89833 in Linux
Summary
by MITRE • 09/16/2026
In the Linux kernel, the following vulnerability has been resolved:
f2fs: fix to avoid potential deadloop in f2fs_fsync_node_pages()
There is potential deadloop in race condition:
Thread A Thread B - fsync - f2fs_do_sync_file - f2fs_fsync_node_pages - last_fsync_dnode - folio_get(last_folio) - f2fs_setattr - f2fs_truncate - f2fs_truncate_blocks - f2fs_do_truncate_blocks - f2fs_truncate_inode_blocks - truncate_dnode - truncate_node - invalidate_mapping_pages - folio->mapping = NULL - is_node_folio alwasy return false - atomic && !marked is always true, then goto retry
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Analysis
by VulDB Data Team • 09/16/2026
The Linux kernel's F2FS file system contains a concurrency flaw within the f2fs_fsync_node_pages function that can lead to an infinite loop under specific race conditions. This vulnerability arises from improper synchronization between filesystem metadata updates and synchronous write operations. When Thread A initiates a file attribute change, it triggers a sequence of truncation functions including f2fs_setattr, f2fs_truncate, and ultimately invalidate_mapping_pages. During this process, the folio mapping pointer is set to NULL as part of the cleanup routine for truncated nodes. Simultaneously, if Thread B executes an fsync operation via f2fs_do_sync_file, it calls f2fs_fsync_node_pages which attempts to retrieve a specific node folio using folio_get. If this race condition occurs such that the target folio has been invalidated by Thread A but not yet fully released or marked appropriately in Thread B's context, the function isochronously checks whether the page is a valid node folio and whether it requires atomic handling without being marked as done.
The core technical flaw lies in the logic governing the retry mechanism within f2fs_fsync_node_pages. The code path evaluates conditions where is_node_folio returns false while the operation is both atomic and not yet marked for completion. Under normal circumstances, these checks help ensure data integrity during synchronization. However, due to the race condition described, the function enters a state where it repeatedly attempts to process pages that are effectively invalid or detached from their mapping structures. Because the folio->mapping pointer has been nullified by the truncation operation in Thread A, subsequent calls within the loop fail to progress correctly and instead trigger a retry logic that never resolves because the underlying resource is no longer accessible in the expected state. This results in an infinite loop where CPU cycles are consumed without making forward progress on the filesystem synchronization task.
From an operational impact perspective, this vulnerability can cause significant system instability for users relying on F2FS storage media, which is commonly used in Android devices and embedded systems with flash storage. The primary consequence of this race condition is a denial of service manifested as a hung process or kernel thread that consumes 100 percent CPU resources related to the affected filesystem operations. In severe cases, if the system relies on watchdog timers for critical services, the infinite loop could trigger hard resets or cause broader system unresponsiveness depending on how deeply integrated the F2FS driver is with other subsystems. While this does not directly allow arbitrary code execution or privilege escalation, it severely degrades availability and reliability of systems utilizing affected kernel versions.
This issue aligns with CWE-835 which describes loops that do not terminate properly due to logic errors in concurrency handling. It also relates to ATT&CK technique T1496 related to resource hijacking through denial-of-service conditions, although the primary classification remains a reliability and stability defect rather than an active exploitation vector for attackers seeking control. The vulnerability highlights challenges inherent in managing complex state transitions within high-concurrency filesystem drivers where multiple threads may manipulate metadata structures simultaneously without adequate locking granularity or memory barrier enforcement.
Mitigation strategies primarily involve applying vendor-provided kernel patches that address the synchronization logic within f2fs_fsync_node_pages. System administrators should ensure their operating systems are updated to versions containing fixes for this specific race condition. For environments unable to immediately patch, monitoring tools can be configured to detect prolonged CPU usage by filesystem-related processes which may indicate such a deadlock scenario is occurring. Additionally, reviewing application behavior that triggers frequent fsync operations on F2FS volumes might help reduce exposure windows until permanent remediation is deployed. Developers working with similar kernel subsystems should review their own concurrency models for analogous patterns where resource invalidation during active processing could lead to non-terminating loops or use-after-free scenarios in other contexts.