CVE-2024-49957 in Linux
Summary
by MITRE • 10/21/2024
In the Linux kernel, the following vulnerability has been resolved:
ocfs2: fix null-ptr-deref when journal load failed.
During the mounting process, if journal_reset() fails because of too short journal, then lead to jbd2_journal_load() fails with NULL j_sb_buffer. Subsequently, ocfs2_journal_shutdown() calls jbd2_journal_flush()->jbd2_cleanup_journal_tail()-> __jbd2_update_log_tail()->jbd2_journal_update_sb_log_tail() ->lock_buffer(journal->j_sb_buffer), resulting in a null-pointer dereference error.
To resolve this issue, we should check the JBD2_LOADED flag to ensure the journal was properly loaded. Additionally, use journal instead of osb->journal directly to simplify the code.
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Analysis
by VulDB Data Team • 03/21/2026
The vulnerability described in CVE-2024-49957 represents a critical null pointer dereference flaw within the Linux kernel's ocfs2 filesystem implementation that occurs during the journal loading process. This issue manifests when the journal_reset() function fails due to an insufficiently sized journal, which subsequently causes jbd2_journal_load() to return with a NULL j_sb_buffer value. The flaw exists in the ocfs2 filesystem driver's handling of journal recovery operations, specifically when the system attempts to shut down a corrupted or improperly initialized journal. The vulnerability stems from improper error handling during the mounting sequence where the kernel fails to validate whether the journal has been successfully loaded before proceeding with subsequent operations that assume the journal structure is properly initialized.
The technical execution of this vulnerability follows a clear chain of function calls that ultimately leads to the null pointer dereference. When journal_reset() fails due to journal size constraints, the jbd2_journal_load() function returns with a NULL j_sb_buffer, which then propagates through the call stack including ocfs2_journal_shutdown(), jbd2_journal_flush(), jbd2_cleanup_journal_tail(), __jbd2_update_log_tail(), jbd2_journal_update_sb_log_tail(), and finally lock_buffer() which attempts to access journal->j_sb_buffer without proper validation. This sequence demonstrates a classic error handling flaw where the code assumes successful initialization without verifying the state of critical data structures. The vulnerability directly maps to CWE-476 which describes null pointer dereference conditions, and represents a failure in proper error state management within the kernel's journal subsystem.
The operational impact of this vulnerability is severe as it can lead to system crashes and potential denial of service conditions in environments utilizing ocfs2 filesystems. Systems running the affected kernel versions may experience unexpected kernel oops or panics when attempting to mount ocfs2 filesystems with corrupted or improperly sized journals, which could be exploited by malicious actors to disrupt services or potentially escalate privileges. The vulnerability affects any system that employs the ocfs2 distributed filesystem implementation, particularly those in high-availability environments where filesystem stability is critical. From an ATT&CK framework perspective, this vulnerability could be leveraged as part of a privilege escalation or denial of service attack vector, potentially allowing adversaries to destabilize systems running ocfs2 filesystems.
The fix implemented for CVE-2024-49957 addresses the root cause by introducing proper validation of the JBD2_LOADED flag before proceeding with journal shutdown operations. This change ensures that the system only attempts to access journal buffers when they have been successfully initialized, preventing the null pointer dereference condition. Additionally, the patch simplifies the code by using the journal parameter directly instead of accessing osb->journal, reducing complexity and potential for similar errors. The mitigation approach aligns with best practices for kernel security by implementing proper error state checking and validation before dereferencing pointers, which is consistent with the principle of defensive programming. Organizations should prioritize applying this kernel update to prevent exploitation of this vulnerability in production environments.