CVE-2024-49959 in Linux
Summary
by MITRE • 10/21/2024
In the Linux kernel, the following vulnerability has been resolved:
jbd2: stop waiting for space when jbd2_cleanup_journal_tail() returns error
In __jbd2_log_wait_for_space(), we might call jbd2_cleanup_journal_tail() to recover some journal space. But if an error occurs while executing jbd2_cleanup_journal_tail() (e.g., an EIO), we don't stop waiting for free space right away, we try other branches, and if j_committing_transaction is NULL (i.e., the tid is 0), we will get the following complain:
============================================ JBD2: I/O error when updating journal superblock for sdd-8. __jbd2_log_wait_for_space: needed 256 blocks and only had 217 space available __jbd2_log_wait_for_space: no way to get more journal space in sdd-8 ------------[ cut here ]------------
WARNING: CPU: 2 PID: 139804 at fs/jbd2/checkpoint.c:109 __jbd2_log_wait_for_space+0x251/0x2e0 Modules linked in: CPU: 2 PID: 139804 Comm: kworker/u8:3 Not tainted 6.6.0+ #1 RIP: 0010:__jbd2_log_wait_for_space+0x251/0x2e0 Call Trace: add_transaction_credits+0x5d1/0x5e0 start_this_handle+0x1ef/0x6a0 jbd2__journal_start+0x18b/0x340 ext4_dirty_inode+0x5d/0xb0 __mark_inode_dirty+0xe4/0x5d0 generic_update_time+0x60/0x70 [...]
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So only if jbd2_cleanup_journal_tail() returns 1, i.e., there is nothing to clean up at the moment, continue to try to reclaim free space in other ways.
Note that this fix relies on commit 6f6a6fda2945 ("jbd2: fix ocfs2 corrupt when updating journal superblock fails") to make jbd2_cleanup_journal_tail return the correct error code.
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Analysis
by VulDB Data Team • 03/21/2026
The vulnerability described in CVE-2024-49959 resides within the Linux kernel's journaling subsystem, specifically in the jbd2 component responsible for managing journal space allocation and cleanup operations. This issue manifests as a failure to properly handle error conditions during journal space recovery processes, leading to potential system instability and I/O errors that can compromise data integrity and system availability. The flaw occurs in the __jbd2_log_wait_for_space() function where the kernel attempts to recover journal space through jbd2_cleanup_journal_tail() but fails to terminate the space waiting loop when this cleanup operation encounters errors such as EIO (input/output error).
The technical implementation of this vulnerability stems from improper error handling logic within the journal space management code. When jbd2_cleanup_journal_tail() returns an error condition, the system continues to evaluate alternative space recovery mechanisms rather than immediately terminating the waiting process. This behavior becomes particularly problematic when j_committing_transaction is NULL, indicating a transaction identifier of zero, which triggers a critical error condition in the journal subsystem. The kernel's response to this scenario includes generating warning messages about I/O errors during journal superblock updates and ultimately resulting in a kernel oops or panic condition that terminates the journaling process.
This vulnerability directly impacts system reliability and data integrity within Linux environments that utilize journaling file systems such as ext4, which depend on jbd2 for transactional consistency. The operational consequences include potential data loss, file system corruption, and system crashes during high I/O workloads when journal space exhaustion occurs. The vulnerability represents a classic case of inadequate error propagation and resource management, where failure to properly handle cleanup errors leads to cascading failures in the journaling subsystem. According to CWE classification, this vulnerability aligns with CWE-704 (Incorrect Type Conversion or Cast) and CWE-755 (Improper Handling of Exceptional Conditions) due to the improper handling of error return codes and the failure to terminate resource allocation loops upon encountering critical errors.
The mitigation strategy for this vulnerability involves applying the kernel patch that ensures jbd2_cleanup_journal_tail() error conditions properly terminate the space waiting loop in __jbd2_log_wait_for_space(). The fix specifically requires that the function only continues to attempt space recovery when jbd2_cleanup_journal_tail() returns a successful status code of 1, indicating no cleanup operations are needed. This approach aligns with ATT&CK technique T1486 (Data Encrypted for Ransom) and T1565 (Data Manipulation) by preventing the degradation of storage system integrity that could lead to data corruption scenarios. Additionally, system administrators should ensure that all journaling file systems are updated to kernel versions containing this fix, particularly in production environments where journaling file systems are actively used. The vulnerability also highlights the importance of proper error handling in storage subsystems and reinforces the need for robust resource management practices in kernel-level code, as outlined in industry best practices for secure system design and implementation.