CVE-2024-40951 in Linux
Summary
by MITRE • 07/12/2024
In the Linux kernel, the following vulnerability has been resolved:
ocfs2: fix NULL pointer dereference in ocfs2_abort_trigger()
bdev->bd_super has been removed and commit 8887b94d9322 change the usage from bdev->bd_super to b_assoc_map->host->i_sb. Since ocfs2 hasn't set bh->b_assoc_map, it will trigger NULL pointer dereference when calling into ocfs2_abort_trigger().
Actually this was pointed out in history, see commit 74e364ad1b13. But I've made a mistake when reviewing commit 8887b94d9322 and then re-introduce this regression.
Since we cannot revive bdev in buffer head, so fix this issue by initializing all types of ocfs2 triggers when fill super, and then get the specific ocfs2 trigger from ocfs2_caching_info when access journal.
[[email protected]: v2]
Link: https://lkml.kernel.org/r/[email protected]
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Analysis
by VulDB Data Team • 08/06/2024
The vulnerability CVE-2024-40951 represents a critical NULL pointer dereference in the Linux kernel's ocfs2 filesystem implementation that arises from improper handling of buffer head associations during filesystem abort operations. This issue specifically impacts the ocfs2_abort_trigger() function where the kernel attempts to access bdev->bd_super which has been deprecated and replaced with b_assoc_map->host->i_sb in commit 8887b94d9322. The root cause occurs when ocfs2 filesystem drivers fail to properly initialize the b_assoc_map field in buffer heads, leading to a scenario where accessing the superblock reference triggers a null pointer dereference. This regression was inadvertently reintroduced during code review of the aforementioned commit, despite previous identification of the issue in commit 74e364ad1b13.
The technical flaw manifests in the ocfs2 filesystem's abort handling mechanism where the kernel attempts to traverse a chain of pointers to reach the superblock information. When b_assoc_map remains uninitialized in buffer heads, the subsequent dereference of b_assoc_map->host->i_sb results in immediate system crash or kernel panic. This vulnerability directly violates the principle of defensive programming as outlined in CWE-476 which addresses NULL pointer dereferences, and represents a classic case of improper resource management in kernel space. The issue affects the core filesystem abort functionality and can potentially lead to complete system instability when the ocfs2 filesystem encounters error conditions requiring abort operations.
Operationally, this vulnerability poses significant risk to systems running ocfs2 filesystems, particularly in enterprise environments where high availability and stable operations are critical. The NULL pointer dereference can occur during normal filesystem operations when error conditions trigger the abort mechanism, potentially leading to denial of service attacks or system crashes that require manual intervention. Attackers could potentially exploit this vulnerability by creating specific conditions that force the filesystem into error states, thereby triggering the NULL pointer dereference and causing system instability. The impact extends beyond simple service disruption to potential data integrity issues when filesystem operations are abruptly terminated.
The mitigation strategy implemented in this fix involves reworking the initialization approach for ocfs2 triggers by ensuring all types of ocfs2 triggers are properly initialized during superblock setup rather than attempting to access deprecated buffer head associations. This approach aligns with ATT&CK technique T1490 which involves data destruction and system instability through kernel-level modifications. The solution specifically addresses the issue by initializing ocfs2 triggers at superblock fill time and retrieving specific triggers from ocfs2_caching_info during journal access operations. This method eliminates the dependency on potentially uninitialized buffer head associations and follows proper kernel development practices for maintaining backward compatibility while avoiding NULL pointer dereference conditions. The fix ensures that all filesystem operations maintain proper pointer validation and resource initialization, preventing the regression from reoccurring in future kernel versions.