CVE-2025-71065 in Linux
Summary
by MITRE • 01/13/2026
In the Linux kernel, the following vulnerability has been resolved:
f2fs: fix to avoid potential deadlock
As Jiaming Zhang and syzbot reported, there is potential deadlock in f2fs as below:
Chain exists of: &sbi->cp_rwsem --> fs_reclaim --> sb_internal#2
Possible unsafe locking scenario:
CPU0 CPU1 ---- ---- rlock(sb_internal#2); lock(fs_reclaim); lock(sb_internal#2); rlock(&sbi->cp_rwsem);
*** DEADLOCK ***
3 locks held by kswapd0/73: #0: ffffffff8e247a40 (fs_reclaim){+.+.}-{0:0}, at: balance_pgdat mm/vmscan.c:7015 [inline]
#0: ffffffff8e247a40 (fs_reclaim){+.+.}-{0:0}, at: kswapd+0x951/0x2800 mm/vmscan.c:7389
#1: ffff8880118400e0 (&type->s_umount_key#50){.+.+}-{4:4}, at: super_trylock_shared fs/super.c:562 [inline]
#1: ffff8880118400e0 (&type->s_umount_key#50){.+.+}-{4:4}, at: super_cache_scan+0x91/0x4b0 fs/super.c:197
#2: ffff888011840610 (sb_internal#2){.+.+}-{0:0}, at: f2fs_evict_inode+0x8d9/0x1b60 fs/f2fs/inode.c:890
stack backtrace: CPU: 0 UID: 0 PID: 73 Comm: kswapd0 Not tainted syzkaller #0 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014 Call Trace: <TASK> dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2043 check_noncircular+0x134/0x160 kernel/locking/lockdep.c:2175 check_prev_add kernel/locking/lockdep.c:3165 [inline]
check_prevs_add kernel/locking/lockdep.c:3284 [inline]
validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868 down_read+0x46/0x2e0 kernel/locking/rwsem.c:1537 f2fs_down_read fs/f2fs/f2fs.h:2278 [inline]
f2fs_lock_op fs/f2fs/f2fs.h:2357 [inline]
f2fs_do_truncate_blocks+0x21c/0x10c0 fs/f2fs/file.c:791 f2fs_truncate_blocks+0x10a/0x300 fs/f2fs/file.c:867 f2fs_truncate+0x489/0x7c0 fs/f2fs/file.c:925 f2fs_evict_inode+0x9f2/0x1b60 fs/f2fs/inode.c:897 evict+0x504/0x9c0 fs/inode.c:810 f2fs_evict_inode+0x1dc/0x1b60 fs/f2fs/inode.c:853 evict+0x504/0x9c0 fs/inode.c:810 dispose_list fs/inode.c:852 [inline]
prune_icache_sb+0x21b/0x2c0 fs/inode.c:1000 super_cache_scan+0x39b/0x4b0 fs/super.c:224 do_shrink_slab+0x6ef/0x1110 mm/shrinker.c:437 shrink_slab_memcg mm/shrinker.c:550 [inline]
shrink_slab+0x7ef/0x10d0 mm/shrinker.c:628 shrink_one+0x28a/0x7c0 mm/vmscan.c:4955 shrink_many mm/vmscan.c:5016 [inline]
lru_gen_shrink_node mm/vmscan.c:5094 [inline]
shrink_node+0x315d/0x3780 mm/vmscan.c:6081 kswapd_shrink_node mm/vmscan.c:6941 [inline]
balance_pgdat mm/vmscan.c:7124 [inline]
kswapd+0x147c/0x2800 mm/vmscan.c:7389 kthread+0x70e/0x8a0 kernel/kthread.c:463 ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 </TASK>
The root cause is deadlock among four locks as below:
kswapd - fs_reclaim --- Lock A - shrink_one - evict - f2fs_evict_inode - sb_start_intwrite --- Lock B
- iput - evict - f2fs_evict_inode - sb_start_intwrite --- Lock B - f2fs_truncate - f2fs_truncate_blocks - f2fs_do_truncate_blocks - f2fs_lock_op --- Lock C
ioctl - f2fs_ioc_commit_atomic_write - f2fs_lock_op --- Lock C - __f2fs_commit_atomic_write - __replace_atomic_write_block - f2fs_get_dnode_of_data - __get_node_folio - f2fs_check_nid_range - f2fs_handle_error - f2fs_record_errors - f2fs_down_write --- Lock D
open - do_open - do_truncate - security_inode_need_killpriv - f2fs_getxattr - lookup_all_xattrs - f2fs_handle_error - f2fs_record_errors - f2fs_down_write --- Lock D - f2fs_commit_super - read_mapping_folio - filemap_alloc_folio_noprof - prepare_alloc_pages - fs_reclaim_acquire --- Lock A
In order to a ---truncated---
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Analysis
by VulDB Data Team • 01/16/2026
The vulnerability CVE-2025-71065 is a deadlock scenario found within the Linux kernel's F2FS (Flash-Friendly File System) implementation. This issue manifests when multiple locking mechanisms interact in a circular dependency, leading to a system-wide stall where threads become indefinitely blocked. The root cause stems from an improper acquisition order of four distinct locks, which creates a cycle that prevents any thread from progressing. The deadlock occurs in the context of memory management and file system operations, specifically involving the kswapd kernel thread responsible for reclaiming memory. The locking chain begins with `fs_reclaim`, proceeds through `f2fs_evict_inode`, and ultimately involves `sb_start_intwrite` and `f2fs_lock_op`, which are critical for maintaining consistency during file truncation and inode eviction. The system's lock validator detects this circular dependency and flags it as a potential deadlock, as demonstrated by the stack trace showing kswapd0 holding three locks and attempting to acquire `&sbi->cp_rwsem` while another path tries to lock `sb_internal#2` after already holding `fs_reclaim`.
The technical flaw arises from the improper ordering of lock acquisition in the F2FS subsystem, particularly in scenarios involving memory pressure and file system cleanup. When kswapd attempts to reclaim memory, it must traverse through the `fs_reclaim` lock, which eventually leads to acquiring `sb_start_intwrite` during inode eviction. Concurrently, another path through the file system can attempt to acquire `f2fs_lock_op` and `f2fs_down_write`, which in turn may require `sb_internal#2` in a way that conflicts with the lock order established by kswapd. This creates a classic deadlock situation where each thread holds a lock that the other requires, rendering the system unresponsive. The issue is particularly severe in high-memory-pressure scenarios where kswapd is actively operating, as it directly impacts system stability and performance. The flaw is categorized under CWE-367, which addresses Time-of-Check to Time-of-Use (TOCTOU) vulnerabilities, but more specifically relates to improper lock ordering and deadlock conditions. This vulnerability can be exploited to cause system hangs or denial of service, especially in embedded systems or virtualized environments where memory management is critical.
The operational impact of this vulnerability extends beyond simple system performance degradation, potentially leading to complete system lockup or unresponsiveness in memory-intensive workloads. The deadlock condition can cause kswapd to stall indefinitely, which in turn prevents the kernel from reclaiming memory effectively, leading to memory exhaustion. This situation is particularly dangerous in production environments where continuous operation is required, as it can result in service interruptions or complete system failure. The vulnerability affects systems running Linux kernels with F2FS file systems, especially those under memory pressure or with high I/O loads. Attackers could potentially trigger this condition through specific file system operations, memory allocation patterns, or by forcing memory reclaim processes to run concurrently with file system cleanup tasks. The ATT&CK framework categorizes this as a system resource exhaustion attack, where the goal is to consume or block critical system resources to prevent normal operation. The vulnerability is particularly concerning because it involves kernel-level locking mechanisms, meaning that exploitation does not require elevated privileges, and the impact is immediate and severe.
Mitigation strategies for CVE-2025-71065 focus on correcting the lock acquisition order and implementing proper synchronization mechanisms within the F2FS subsystem. The recommended solution involves modifying the kernel code to enforce a consistent lock ordering across all paths that can lead to deadlock conditions. This includes reordering the acquisition of `f2fs_lock_op` and `f2fs_down_write` to ensure they are always acquired before `fs_reclaim` or `sb_start_intwrite`. Additionally, kernel developers should implement lock validation checks and potentially introduce timeout mechanisms for lock acquisition to prevent indefinite blocking. The most effective approach is to patch the F2FS implementation to ensure that all locking paths follow a consistent and well-defined order, eliminating the circular dependency. System administrators should monitor memory usage and I/O patterns to detect early signs of potential deadlock conditions, and ensure that systems are updated with the latest kernel patches. The fix should also include enhanced logging for lock acquisition failures to aid in debugging and monitoring. For environments where the vulnerability cannot be immediately patched, administrators should consider reducing memory pressure or limiting concurrent file system operations that could trigger the deadlock condition. The mitigation aligns with best practices in kernel security, emphasizing the importance of proper lock ordering and deadlock prevention in multi-threaded systems.