CVE-2025-68178 in Linux
Summary
by MITRE • 12/16/2025
In the Linux kernel, the following vulnerability has been resolved:
blk-cgroup: fix possible deadlock while configuring policy
Following deadlock can be triggered easily by lockdep:
WARNING: possible circular locking dependency detected 6.17.0-rc3-00124-ga12c2658ced0 #1665 Not tainted ------------------------------------------------------ check/1334 is trying to acquire lock: ff1100011d9d0678 (&q->sysfs_lock){+.+.}-{4:4}, at: blk_unregister_queue+0x53/0x180
but task is already holding lock: ff1100011d9d00e0 (&q->q_usage_counter(queue)#3){++++}-{0:0}, at: del_gendisk+0xba/0x110
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #2 (&q->q_usage_counter(queue)#3){++++}-{0:0}:
blk_queue_enter+0x40b/0x470 blkg_conf_prep+0x7b/0x3c0 tg_set_limit+0x10a/0x3e0 cgroup_file_write+0xc6/0x420 kernfs_fop_write_iter+0x189/0x280 vfs_write+0x256/0x490 ksys_write+0x83/0x190 __x64_sys_write+0x21/0x30 x64_sys_call+0x4608/0x4630 do_syscall_64+0xdb/0x6b0 entry_SYSCALL_64_after_hwframe+0x76/0x7e
-> #1 (&q->rq_qos_mutex){+.+.}-{4:4}:
__mutex_lock+0xd8/0xf50 mutex_lock_nested+0x2b/0x40 wbt_init+0x17e/0x280 wbt_enable_default+0xe9/0x140 blk_register_queue+0x1da/0x2e0 __add_disk+0x38c/0x5d0 add_disk_fwnode+0x89/0x250 device_add_disk+0x18/0x30 virtblk_probe+0x13a3/0x1800 virtio_dev_probe+0x389/0x610 really_probe+0x136/0x620 __driver_probe_device+0xb3/0x230 driver_probe_device+0x2f/0xe0 __driver_attach+0x158/0x250 bus_for_each_dev+0xa9/0x130 driver_attach+0x26/0x40 bus_add_driver+0x178/0x3d0 driver_register+0x7d/0x1c0 __register_virtio_driver+0x2c/0x60 virtio_blk_init+0x6f/0xe0 do_one_initcall+0x94/0x540 kernel_init_freeable+0x56a/0x7b0 kernel_init+0x2b/0x270 ret_from_fork+0x268/0x4c0 ret_from_fork_asm+0x1a/0x30
-> #0 (&q->sysfs_lock){+.+.}-{4:4}:
__lock_acquire+0x1835/0x2940 lock_acquire+0xf9/0x450 __mutex_lock+0xd8/0xf50 mutex_lock_nested+0x2b/0x40 blk_unregister_queue+0x53/0x180 __del_gendisk+0x226/0x690 del_gendisk+0xba/0x110 sd_remove+0x49/0xb0 [sd_mod]
device_remove+0x87/0xb0 device_release_driver_internal+0x11e/0x230 device_release_driver+0x1a/0x30 bus_remove_device+0x14d/0x220 device_del+0x1e1/0x5a0 __scsi_remove_device+0x1ff/0x2f0 scsi_remove_device+0x37/0x60 sdev_store_delete+0x77/0x100 dev_attr_store+0x1f/0x40 sysfs_kf_write+0x65/0x90 kernfs_fop_write_iter+0x189/0x280 vfs_write+0x256/0x490 ksys_write+0x83/0x190 __x64_sys_write+0x21/0x30 x64_sys_call+0x4608/0x4630 do_syscall_64+0xdb/0x6b0 entry_SYSCALL_64_after_hwframe+0x76/0x7e
other info that might help us debug this:
Chain exists of: &q->sysfs_lock --> &q->rq_qos_mutex --> &q->q_usage_counter(queue)#3
Possible unsafe locking scenario:
CPU0 CPU1 ---- ---- lock(&q->q_usage_counter(queue)#3); lock(&q->rq_qos_mutex); lock(&q->q_usage_counter(queue)#3); lock(&q->sysfs_lock);
Root cause is that queue_usage_counter is grabbed with rq_qos_mutex held in blkg_conf_prep(), while queue should be freezed before rq_qos_mutex from other context.
The blk_queue_enter() from blkg_conf_prep() is used to protect against policy deactivation, which is already protected with blkcg_mutex, hence convert blk_queue_enter() to blkcg_mutex to fix this problem. Meanwhile, consider that blkcg_mutex is held after queue is freezed from policy deactivation, also convert blkg_alloc() to use GFP_NOIO.
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Analysis
by VulDB Data Team • 02/21/2026
The vulnerability described in CVE-2025-68178 resides within the Linux kernel's block layer subsystem, specifically in the blk-cgroup functionality responsible for managing I/O control policies. This issue manifests as a potential deadlock condition that can occur during the configuration of I/O policies, particularly when the system attempts to register or unregister block queues while other I/O operations are in progress. The vulnerability was identified through lockdep, a kernel subsystem designed to detect potential deadlock scenarios by monitoring lock acquisition patterns and dependencies.
The technical flaw stems from a circular locking dependency involving three distinct kernel locks: q_usage_counter, rq_qos_mutex, and sysfs_lock. During normal operation, when a block queue is being unregistered, the system attempts to acquire the sysfs_lock while already holding the q_usage_counter lock. However, the q_usage_counter lock is also held by another context that is trying to acquire the rq_qos_mutex lock, which in turn is needed to acquire the sysfs_lock, creating a circular dependency. This chain of dependencies is particularly problematic because it occurs during device removal operations, such as when SCSI devices are being removed from the system, where the kernel attempts to clean up resources while maintaining consistency across I/O policies.
The operational impact of this vulnerability is significant, as it can lead to system hangs or deadlocks that prevent normal system operation. The deadlock occurs when the kernel attempts to configure I/O policies during device removal, causing the system to become unresponsive until the deadlock is resolved through external intervention or system reboot. This is particularly concerning in production environments where device hot-plugging or device removal operations are common, such as in storage arrays or virtualized environments. The vulnerability affects systems using the blk-cgroup functionality, which is integral to I/O control and resource management in modern Linux systems, making it a critical issue for system stability.
The root cause analysis reveals that the issue originates from the blkg_conf_prep() function, which acquires the q_usage_counter lock while holding the rq_qos_mutex. The fix implemented addresses this by converting the blk_queue_enter() call to use blkcg_mutex instead of the problematic locking sequence. This change ensures that queue operations are properly synchronized without creating the circular dependency. Additionally, the fix modifies blkg_alloc() to use GFP_NOIO allocation flags to prevent potential I/O operations during memory allocation, which could further complicate the locking scenario. This solution aligns with the principles of lock ordering and prevents the problematic acquisition sequence that leads to the deadlock. The fix is consistent with established kernel development practices for managing complex locking dependencies and follows the ATT&CK framework's principle of maintaining system stability through proper resource management, particularly in the context of device management and I/O subsystem operations. This vulnerability demonstrates the complexity of maintaining proper locking semantics in kernel subsystems where multiple layers of I/O control and resource management intersect.