CVE-2024-40969 in Linux
Summary
by MITRE • 07/12/2024
In the Linux kernel, the following vulnerability has been resolved:
f2fs: don't set RO when shutting down f2fs
Shutdown does not check the error of thaw_super due to readonly, which causes a deadlock like below.
f2fs_ioc_shutdown(F2FS_GOING_DOWN_FULLSYNC) issue_discard_thread - bdev_freeze - freeze_super - f2fs_stop_checkpoint() - f2fs_handle_critical_error - sb_start_write - set RO - waiting - bdev_thaw - thaw_super_locked - return -EINVAL, if sb_rdonly() - f2fs_stop_discard_thread -> wait for kthread_stop(discard_thread);
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Analysis
by VulDB Data Team • 09/09/2024
The vulnerability CVE-2024-40969 represents a critical deadlock condition in the Linux kernel's f2fs (Flash-Friendly File System) implementation that can lead to system unresponsiveness during shutdown operations. This issue specifically manifests when the file system attempts to handle shutdown procedures while dealing with read-only mount states, creating a circular dependency that prevents proper system termination. The flaw occurs during the f2fs_ioc_shutdown operation with F2FS_GOING_DOWN_FULLSYNC flag, where the shutdown process fails to properly check error conditions from thaw_super operations, resulting in a system-wide deadlock scenario.
The technical root cause stems from improper error handling within the f2fs shutdown sequence where the system fails to verify the return status of thaw_super operations before proceeding with shutdown procedures. When the shutdown process attempts to freeze and then thaw the superblock, it encounters a condition where thaw_super_locked returns -EINVAL when the superblock is read-only, but this error is not properly handled. The deadlock occurs because f2fs_stop_checkpoint attempts to set the read-only flag while waiting for a lock that never releases due to the frozen state, while f2fs_stop_discard_thread waits for the discard thread to stop, creating a circular dependency that blocks the entire system.
This vulnerability has significant operational impact as it can cause complete system hangs during shutdown procedures, particularly affecting embedded systems, mobile devices, and servers that rely on f2fs for storage operations. The issue is particularly dangerous in environments where automatic shutdowns or system reboots are common, as it can render systems unresponsive and require manual intervention or power cycling. The deadlock scenario described in the vulnerability affects the entire kernel subsystem, making it a critical issue that can compromise system availability and reliability in production environments.
The mitigation strategy for this vulnerability involves ensuring proper error handling in the f2fs shutdown sequence by implementing checks for thaw_super return values before proceeding with read-only flag setting operations. System administrators should apply the kernel patches that address this specific deadlock condition, which typically involve modifying the shutdown procedure to properly handle error conditions from superblock operations and avoid circular dependency scenarios. Organizations should prioritize patching systems running f2fs file systems, particularly those in mission-critical environments where system availability is paramount, as the vulnerability can lead to complete system lockups during routine shutdown operations.
This vulnerability aligns with CWE-362, which describes "Concurrent Execution using Shared Resource with Improper Synchronization," as the deadlock occurs due to improper synchronization between multiple system components during shutdown procedures. The issue also relates to ATT&CK technique T1490, "Inhibit System Recovery," as the system unresponsiveness during shutdown can prevent normal recovery procedures from completing successfully. The f2fs implementation demonstrates a classic example of improper resource management where the file system fails to properly release locks and resources during critical shutdown operations, leading to system-wide blocking conditions that can persist until manual intervention occurs.