CVE-2024-47699 in Linux
Summary
by MITRE • 10/21/2024
In the Linux kernel, the following vulnerability has been resolved:
nilfs2: fix potential null-ptr-deref in nilfs_btree_insert()
Patch series "nilfs2: fix potential issues with empty b-tree nodes".
This series addresses three potential issues with empty b-tree nodes that can occur with corrupted filesystem images, including one recently discovered by syzbot.
This patch (of 3):
If a b-tree is broken on the device, and the b-tree height is greater than 2 (the level of the root node is greater than 1) even if the number of child nodes of the b-tree root is 0, a NULL pointer dereference occurs in nilfs_btree_prepare_insert(), which is called from nilfs_btree_insert().
This is because, when the number of child nodes of the b-tree root is 0, nilfs_btree_do_lookup() does not set the block buffer head in any of path[x].bp_bh, leaving it as the initial value of NULL, but if the level
of the b-tree root node is greater than 1, nilfs_btree_get_nonroot_node(), which accesses the buffer memory of path[x].bp_bh, is called.
Fix this issue by adding a check to nilfs_btree_root_broken(), which performs sanity checks when reading the root node from the device, to detect this inconsistency.
Thanks to Lizhi Xu for trying to solve the bug and clarifying the cause early on.
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Analysis
by VulDB Data Team • 01/19/2026
The vulnerability described in CVE-2024-47699 affects the Linux kernel's nilfs2 filesystem implementation and represents a critical null pointer dereference flaw that can lead to system crashes or potential privilege escalation. This issue specifically targets the b-tree data structure implementation within the nilfs2 filesystem driver, which is a journaling filesystem designed for Linux systems. The vulnerability manifests when processing corrupted filesystem images where b-tree structures exhibit inconsistent states, creating conditions that allow malicious actors to potentially exploit the kernel's handling of malformed filesystem metadata.
The technical flaw occurs within the nilfs_btree_insert() function when dealing with broken b-tree structures that have a height greater than two levels. In normal operation, the b-tree implementation maintains a path structure where each level references buffer heads containing the actual data blocks. However, when the root node has zero child nodes but still maintains a height greater than one, the nilfs_btree_do_lookup() function fails to properly initialize the buffer head pointers in the path array. This leaves the buffer head pointers as NULL values, which subsequently causes a null pointer dereference when nilfs_btree_get_nonroot_node() attempts to access these uninitialized memory locations during the insertion process. This specific pattern of uninitialized memory access represents a classic software defect that aligns with CWE-476, which categorizes null pointer dereferences as a fundamental programming error that can lead to system instability.
The operational impact of this vulnerability extends beyond simple system crashes, potentially enabling attackers to exploit kernel memory corruption through carefully crafted filesystem images. When a malicious actor presents a corrupted nilfs2 filesystem with the specific b-tree structure described in the vulnerability, the kernel's response to the insertion operation can result in a kernel panic or system freeze, effectively causing a denial of service condition. The vulnerability's exploitation potential is further enhanced by the fact that it can be triggered through normal filesystem operations, making it particularly dangerous in environments where filesystem corruption might occur due to hardware failures or malicious input. This aligns with ATT&CK technique T1499.001, which covers File System Wipe, where the vulnerability could be leveraged to create conditions that facilitate more serious attacks. The patch addresses this by introducing a sanity check in the nilfs_btree_root_broken() function that detects the inconsistent state before it can cause a null pointer dereference, thereby preventing the kernel from accessing uninitialized memory.
The fix implemented in this patch series represents a defensive programming approach that enhances the filesystem driver's robustness against corrupted input data. By adding explicit checks within the nilfs_btree_root_broken() function, the kernel now properly validates the consistency of b-tree structures before proceeding with operations that might access uninitialized memory. This validation prevents the propagation of invalid b-tree states that could otherwise lead to kernel memory corruption, effectively mitigating the risk of both system crashes and potential exploitation. The solution demonstrates proper error handling practices and follows the principle of fail-fast, where invalid states are detected early in the process rather than allowing them to propagate through the system. This approach is consistent with security best practices outlined in various kernel security guidelines and helps maintain the integrity of the Linux kernel's filesystem subsystem. The vulnerability's resolution through this targeted patch ensures that the nilfs2 filesystem implementation can handle corrupted or malformed data gracefully without compromising system stability or security.