CVE-2026-68459 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
f2fs: fix potential deadlock in gc_merge path of f2fs_balance_fs()
When we mount device w/ gc_merge mount option, we may suffer below potential deadlock:
Kworker GC trehad Truncator - f2fs_write_cache_pages - f2fs_write_single_data_page - f2fs_do_write_data_page - folio_start_writeback --- set writeback flag on folio - f2fs_outplace_write_data : cached folio in internal bio cache - f2fs_balance_fs - wake_up(gc_thread) : wake up gc thread to run foreground GC - finish_wait(fggc_wq) : wait on the waitqueue --- wait on GC thread to finish the work - truncate_inode_pages_range - __filemap_get_folio(, FGP_LOCK) --- lock folio - truncate_inode_partial_folio - folio_wait_writeback --- wait on writeback being cleared - do_garbage_collect - move_data_page - f2fs_get_lock_data_folio - lock on folio --- blocked on folio's lock
In order to avoid such deadlock, let's call below functions to commit cached bios in GC_MERGE path of f2fs_balance_fs() as the same as we did in NOGC_MERGE path. - f2fs_submit_merged_write(sbi, DATA); - f2fs_submit_all_merged_ipu_writes(sbi);
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Analysis
by VulDB Data Team • 08/15/2026
The vulnerability exists within the f2fs filesystem implementation in the Linux kernel where a potential deadlock can occur during garbage collection operations when the gc_merge mount option is enabled. This issue manifests through complex interactions between multiple kernel threads and locking mechanisms that create circular wait conditions. The problem specifically affects the f2fs_balance_fs() function which handles foreground garbage collection operations, creating a scenario where the kernel worker thread and garbage collection thread become deadlocked due to conflicting lock acquisition patterns.
The deadlock condition arises from the interplay between several key kernel components including the kworker thread responsible for background I/O operations, the GC thread managing foreground garbage collection, and the truncator process handling file truncation operations. When f2fs_write_cache_pages() is invoked during data page writing, it sets writeback flags on folios and caches them in an internal bio cache structure. The subsequent call to f2fs_balance_fs() triggers a wake_up operation on the GC thread, but this causes the calling thread to wait on a waitqueue for the garbage collection to complete. However, the GC thread itself becomes blocked when attempting to acquire locks on folios that are already held by the truncator process during truncate_inode_pages_range operations.
This particular vulnerability represents a classic deadlock scenario classified under CWE-362 (Concurrent Execution using Shared Resources) and aligns with ATT&CK technique T1490 (Inhibit System Recovery) as it can lead to system unresponsiveness and potential denial of service conditions. The root cause stems from the inconsistent handling of cached bio submissions between different code paths within the f2fs_balance_fs() function, where the GC_MERGE path fails to properly commit cached I/O operations before proceeding with the garbage collection process.
The mitigation strategy involves ensuring consistent behavior across both GC_MERGE and NOGC_MERGE code paths by explicitly calling f2fs_submit_merged_write() and f2fs_submit_all_merged_ipu_writes() functions within the GC_MERGE path of f2fs_balance_fs(). These function calls ensure that all cached bio operations are properly submitted and completed before proceeding with garbage collection, thereby breaking the circular dependency that leads to the deadlock condition. This approach aligns with security best practices for preventing race conditions and resource contention in kernel-level filesystem implementations.
The operational impact of this vulnerability extends beyond simple performance degradation to potentially causing complete system lockups or unresponsiveness, particularly under heavy I/O workloads where file truncation and garbage collection operations occur concurrently. Systems utilizing f2fs with gc_merge enabled are most susceptible to this condition, making it critical for administrators to apply the patch that standardizes the bio submission behavior across all code paths. The fix ensures proper synchronization between different kernel subsystems while maintaining the intended functionality of the garbage collection merge optimization feature.