CVE-2023-53149 in Linux
Summary
by MITRE • 09/15/2025
In the Linux kernel, the following vulnerability has been resolved:
ext4: avoid deadlock in fs reclaim with page writeback
Ext4 has a filesystem wide lock protecting ext4_writepages() calls to avoid races with switching of journalled data flag or inode format. This lock can however cause a deadlock like:
CPU0 CPU1
ext4_writepages() percpu_down_read(sbi->s_writepages_rwsem); ext4_change_inode_journal_flag() percpu_down_write(sbi->s_writepages_rwsem); - blocks, all readers block from now on ext4_do_writepages() ext4_init_io_end() kmem_cache_zalloc(io_end_cachep, GFP_KERNEL) fs_reclaim frees dentry... dentry_unlink_inode() iput() - last ref => iput_final() - inode dirty => write_inode_now()... ext4_writepages() tries to acquire sbi->s_writepages_rwsem and blocks forever
Make sure we cannot recurse into filesystem reclaim from writeback code to avoid the deadlock.
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Analysis
by VulDB Data Team • 01/10/2026
The vulnerability CVE-2023-53149 represents a critical deadlock condition within the ext4 filesystem implementation of the Linux kernel that stems from improper locking mechanisms during concurrent filesystem operations. This issue manifests when the filesystem attempts to manage writeback operations while simultaneously handling journal flag changes, creating a circular dependency that prevents further execution. The problem specifically affects the ext4 filesystem's ability to handle concurrent access patterns where multiple CPU cores attempt to acquire the same locking resources in different orders, leading to a complete system hang situation.
The technical flaw occurs within the ext4 filesystem's locking hierarchy where a percpu_rw_semaphore named sbi->s_writepages_rwsem serves as a global lock protecting ext4_writepages() operations. This lock prevents race conditions during journal flag modifications and inode format changes but becomes problematic when the filesystem reclaim process attempts to acquire the same lock from within the writeback code path. The deadlock scenario emerges when CPU0 holds the writepages_rwsem lock while attempting to process writepages, but CPU1 attempts to acquire the same lock during journal flag changes, creating a circular dependency where each process waits indefinitely for the other to release the resource.
This vulnerability directly impacts system stability and availability by causing complete system hangs when the deadlock conditions are triggered. The operational consequences extend beyond simple performance degradation to potentially complete system lockups, particularly in environments with high I/O workloads where writeback operations and journal flag modifications occur concurrently. The issue is particularly concerning in production systems where filesystem reclaim operations are frequent, as even a single occurrence can lead to extended downtime and service disruption.
The root cause of this vulnerability aligns with CWE-367, which describes Time-of-Check to Time-of-Use (TOCTOU) vulnerabilities and improper locking mechanisms that can lead to deadlocks. This flaw demonstrates the classic pattern of recursive locking where filesystem reclaim code attempts to acquire locks that are already held by the same execution context, creating an unavoidable deadlock scenario. From an ATT&CK framework perspective, this vulnerability could be leveraged in denial-of-service attacks targeting Linux systems with ext4 filesystems, potentially allowing attackers to cause system unavailability through carefully crafted I/O workloads.
The mitigation approach involves restructuring the locking mechanisms to prevent recursive acquisition of the same lock from different code paths. The solution requires ensuring that filesystem reclaim operations cannot enter the writeback code path while holding the writepages_rwsem lock, thereby breaking the circular dependency. This typically involves implementing proper lock ordering policies or introducing additional synchronization primitives that prevent the recursive locking scenario. System administrators should update to kernel versions that contain the patched implementation, as the fix involves modifying the core filesystem locking behavior to eliminate the potential for such deadlocks during concurrent writeback and journal flag modification operations.