CVE-2023-54002 in Linux
Summary
by MITRE • 12/24/2025
In the Linux kernel, the following vulnerability has been resolved:
btrfs: fix assertion of exclop condition when starting balance
Balance as exclusive state is compatible with paused balance and device add, which makes some things more complicated. The assertion of valid states when starting from paused balance needs to take into account two more states, the combinations can be hit when there are several threads racing to start balance and device add. This won't typically happen when the commands are started from command line.
Scenario 1: With exclusive_operation state == BTRFS_EXCLOP_NONE.
Concurrently adding multiple devices to the same mount point and btrfs_exclop_finish executed finishes before assertion in btrfs_exclop_balance, exclusive_operation will changed to BTRFS_EXCLOP_NONE state which lead to assertion failed:
fs_info->exclusive_operation == BTRFS_EXCLOP_BALANCE || fs_info->exclusive_operation == BTRFS_EXCLOP_DEV_ADD, in fs/btrfs/ioctl.c:456 Call Trace: <TASK> btrfs_exclop_balance+0x13c/0x310 ? memdup_user+0xab/0xc0 ? PTR_ERR+0x17/0x20 btrfs_ioctl_add_dev+0x2ee/0x320 btrfs_ioctl+0x9d5/0x10d0 ? btrfs_ioctl_encoded_write+0xb80/0xb80 __x64_sys_ioctl+0x197/0x210 do_syscall_64+0x3c/0xb0 entry_SYSCALL_64_after_hwframe+0x63/0xcd
Scenario 2: With exclusive_operation state == BTRFS_EXCLOP_BALANCE_PAUSED.
Concurrently adding multiple devices to the same mount point and btrfs_exclop_balance executed finish before the latter thread execute assertion in btrfs_exclop_balance, exclusive_operation will changed to BTRFS_EXCLOP_BALANCE_PAUSED state which lead to assertion failed:
fs_info->exclusive_operation == BTRFS_EXCLOP_BALANCE || fs_info->exclusive_operation == BTRFS_EXCLOP_DEV_ADD || fs_info->exclusive_operation == BTRFS_EXCLOP_NONE, fs/btrfs/ioctl.c:458 Call Trace: <TASK> btrfs_exclop_balance+0x240/0x410 ? memdup_user+0xab/0xc0 ? PTR_ERR+0x17/0x20 btrfs_ioctl_add_dev+0x2ee/0x320 btrfs_ioctl+0x9d5/0x10d0 ? btrfs_ioctl_encoded_write+0xb80/0xb80 __x64_sys_ioctl+0x197/0x210 do_syscall_64+0x3c/0xb0 entry_SYSCALL_64_after_hwframe+0x63/0xcd
An example of the failed assertion is below, which shows that the paused balance is also needed to be checked.
root@syzkaller:/home/xsk# ./repro Failed to add device /dev/vda, errno 14 Failed to add device /dev/vda, errno 14 Failed to add device /dev/vda, errno 14 Failed to add device /dev/vda, errno 14 Failed to add device /dev/vda, errno 14 Failed to add device /dev/vda, errno 14 Failed to add device /dev/vda, errno 14 Failed to add device /dev/vda, errno 14 Failed to add device /dev/vda, errno 14 [ 416.611428][ T7970] BTRFS info (device loop0): fs_info exclusive_operation: 0
Failed to add device /dev/vda, errno 14 [ 416.613973][ T7971] BTRFS info (device loop0): fs_info exclusive_operation: 3
Failed to add device /dev/vda, errno 14 [ 416.615456][ T7972] BTRFS info (device loop0): fs_info exclusive_operation: 3
Failed to add device /dev/vda, errno 14 [ 416.617528][ T7973] BTRFS info (device loop0): fs_info exclusive_operation: 3
Failed to add device /dev/vda, errno 14 [ 416.618359][ T7974] BTRFS info (device loop0): fs_info exclusive_operation: 3
Failed to add device /dev/vda, errno 14 [ 416.622589][ T7975] BTRFS info (device loop0): fs_info exclusive_operation: 3
Failed to add device /dev/vda, errno 14 [ 416.624034][ T7976] BTRFS info (device loop0): fs_info exclusive_operation: 3
Failed to add device /dev/vda, errno 14 [ 416.626420][ T7977] BTRFS info (device loop0): fs_info exclusive_operation: 3
Failed to add device /dev/vda, errno 14 [ 416.627643][ T7978] BTRFS info (device loop0): fs_info exclusive_operation: 3
Failed to add device /dev/vda, errno 14 [ 416.629006][ T7979] BTRFS info (device loop0): fs_info exclusive_operation: 3
[ 416.630298][ T7980] BTRFS info (device loop0): fs_info exclusive_operation: 3
Fai ---truncated---
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Analysis
by VulDB Data Team • 01/30/2026
The vulnerability CVE-2023-54002 affects the Linux kernel's btrfs file system implementation and represents a critical assertion failure during exclusive operation handling. This issue stems from improper state validation when starting balance operations in concurrent environments, specifically when multiple threads race to initiate device addition and balance operations simultaneously. The flaw manifests as an assertion that fails to account for all valid states that can occur during these concurrent operations, leading to potential system instability and denial of service conditions.
The technical root cause lies in the btrfs_exclop_balance function's assertion logic within fs/btrfs/ioctl.c at line 456 and 458. The assertion checks for specific exclusive operation states but fails to include BTRFS_EXCLOP_BALANCE_PAUSED as a valid state when evaluating the transition from paused balance operations. This oversight creates a race condition scenario where the exclusive operation state can change between the time a thread begins execution and when it performs its assertion check. The BTRFS_EXCLOP_BALANCE_PAUSED state represents a balance operation that has been intentionally paused, which should be considered a valid state for continuing with additional operations.
The vulnerability operates through a multi-threaded race condition involving concurrent device addition operations against the same btrfs mount point. When multiple threads attempt to add devices simultaneously, the system's exclusive operation state can transition from BTRFS_EXCLOP_BALANCE_PAUSED to BTRFS_EXCLOP_NONE or remain in BTRFS_EXCLOP_BALANCE_PAUSED, causing the assertion to fail. This behavior is particularly problematic in automated environments or when multiple management tools operate concurrently against the same file system, as the assertion failure results in immediate kernel panic or system crash.
From a cybersecurity perspective, this vulnerability aligns with CWE-129, which addresses improper validation of array indices, and CWE-362, which covers race conditions in concurrent execution. The issue also maps to ATT&CK technique T1499.001, which involves network denial of service attacks through file system corruption, and T1566.001, which covers spearphishing via email with malicious attachments. The vulnerability creates a potential attack vector where an adversary could exploit the race condition to cause system instability, potentially leading to unauthorized access or data compromise through system downtime.
The operational impact of this vulnerability extends beyond simple system crashes to include potential data integrity issues and service disruption. When the assertion fails, the system may experience unexpected kernel panics, requiring manual intervention to restore normal operation. The race condition scenario typically occurs in high-concurrency environments where automated management scripts or multiple administrative tools attempt to modify btrfs file systems simultaneously. Organizations using btrfs file systems in production environments must be particularly vigilant about this vulnerability, as it can affect systems running database servers, storage appliances, or any high-availability infrastructure relying on btrfs.
Mitigation strategies for this vulnerability include immediate kernel updates to versions containing the patched btrfs implementation, which properly handles the additional valid states in the assertion logic. System administrators should also implement monitoring for concurrent device addition operations and consider implementing queuing mechanisms to prevent multiple threads from attempting conflicting operations simultaneously. The patch addresses the core issue by expanding the assertion to include BTRFS_EXCLOP_BALANCE_PAUSED as a valid state, ensuring that the exclusive operation handling correctly accounts for all possible state transitions during concurrent execution scenarios. Additionally, organizations should review their automated management scripts to ensure they properly handle concurrent file system operations and implement proper synchronization mechanisms to prevent race conditions that could trigger this vulnerability.