CVE-2024-50265 in Linux
Summary
by MITRE • 11/19/2024
In the Linux kernel, the following vulnerability has been resolved:
ocfs2: remove entry once instead of null-ptr-dereference in ocfs2_xa_remove()
Syzkaller is able to provoke null-ptr-dereference in ocfs2_xa_remove():
[ 57.319872] (a.out,1161,7):ocfs2_xa_remove:2028 ERROR: status = -12
[ 57.320420] (a.out,1161,7):ocfs2_xa_cleanup_value_truncate:1999 ERROR: Partial truncate while removing xattr overlay.upper. Leaking 1 clusters and removing the entry
[ 57.321727] BUG: kernel NULL pointer dereference, address: 0000000000000004
[...]
[ 57.325727] RIP: 0010:ocfs2_xa_block_wipe_namevalue+0x2a/0xc0
[...]
[ 57.331328] Call Trace:
[ 57.331477]
[...]
[ 57.333511] ? do_user_addr_fault+0x3e5/0x740
[ 57.333778] ? exc_page_fault+0x70/0x170
[ 57.334016] ? asm_exc_page_fault+0x2b/0x30
[ 57.334263] ? __pfx_ocfs2_xa_block_wipe_namevalue+0x10/0x10
[ 57.334596] ? ocfs2_xa_block_wipe_namevalue+0x2a/0xc0
[ 57.334913] ocfs2_xa_remove_entry+0x23/0xc0
[ 57.335164] ocfs2_xa_set+0x704/0xcf0
[ 57.335381] ? _raw_spin_unlock+0x1a/0x40
[ 57.335620] ? ocfs2_inode_cache_unlock+0x16/0x20
[ 57.335915] ? trace_preempt_on+0x1e/0x70
[ 57.336153] ? start_this_handle+0x16c/0x500
[ 57.336410] ? preempt_count_sub+0x50/0x80
[ 57.336656] ? _raw_read_unlock+0x20/0x40
[ 57.336906] ? start_this_handle+0x16c/0x500
[ 57.337162] ocfs2_xattr_block_set+0xa6/0x1e0
[ 57.337424] __ocfs2_xattr_set_handle+0x1fd/0x5d0
[ 57.337706] ? ocfs2_start_trans+0x13d/0x290
[ 57.337971] ocfs2_xattr_set+0xb13/0xfb0
[ 57.338207] ? dput+0x46/0x1c0
[ 57.338393] ocfs2_xattr_trusted_set+0x28/0x30
[ 57.338665] ? ocfs2_xattr_trusted_set+0x28/0x30
[ 57.338948] __vfs_removexattr+0x92/0xc0
[ 57.339182] __vfs_removexattr_locked+0xd5/0x190
[ 57.339456] ? preempt_count_sub+0x50/0x80
[ 57.339705] vfs_removexattr+0x5f/0x100
[...]
Reproducer uses faultinject facility to fail ocfs2_xa_remove() -> ocfs2_xa_value_truncate() with -ENOMEM.
In this case the comment mentions that we can return 0 if ocfs2_xa_cleanup_value_truncate() is going to wipe the entry anyway. But the following 'rc' check is wrong and execution flow do 'ocfs2_xa_remove_entry(loc);' twice: * 1st: in ocfs2_xa_cleanup_value_truncate(); * 2nd: returning back to ocfs2_xa_remove() instead of going to 'out'.
Fix this by skipping the 2nd removal of the same entry and making syzkaller repro happy.
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Analysis
by VulDB Data Team • 10/22/2025
The vulnerability described in CVE-2024-50265 affects the Linux kernel's ocfs2 (Oracle Cluster File System 2) implementation, specifically within the ocfs2_xa_remove() function. This issue manifests as a null pointer dereference during extended attribute operations, representing a critical kernel-level flaw that can lead to system instability or potential exploitation. The vulnerability was identified through syzkaller, an automated fuzzer that systematically tests kernel code paths to uncover memory safety issues and other defects. The problem occurs when the kernel attempts to remove extended attributes from ocfs2 filesystem entries while handling memory allocation failures during attribute truncation operations.
The technical root cause stems from improper handling of error conditions within the extended attribute removal code path. When ocfs2_xa_remove() invokes ocfs2_xa_value_truncate() and receives an -ENOMEM error, the code attempts to clean up by calling ocfs2_xa_cleanup_value_truncate(). This cleanup function properly removes the entry but sets a return code that incorrectly flows back to the main removal function. The flawed logic causes the system to attempt removing the same extended attribute entry twice, first in the cleanup function and then again in the main ocfs2_xa_remove() function. This double removal creates a scenario where the kernel attempts to dereference a null pointer, leading to the kernel NULL pointer dereference panic that terminates the system's stability.
The operational impact of this vulnerability extends beyond simple system crashes, as it represents a potential denial of service vector that could be exploited by malicious actors. The vulnerability affects systems running the Linux kernel with ocfs2 filesystem support, particularly those that handle extended attributes frequently or under memory pressure conditions. According to the ATT&CK framework, this vulnerability maps to techniques involving privilege escalation and system stability compromise through kernel exploitation. The CWE classification for this issue would be CWE-476, representing a null pointer dereference, which is a common vector for system instability and potential privilege escalation. The vulnerability's exploitation path through the faultinject facility demonstrates how memory allocation failures can be leveraged to trigger kernel-level memory safety issues.
Mitigation strategies for this vulnerability require kernel updates that implement the fix for the double removal issue in ocfs2_xa_remove(). The patch ensures that when ocfs2_xa_cleanup_value_truncate() performs its cleanup and removes the entry, the main ocfs2_xa_remove() function skips the subsequent removal attempt to prevent the double-free scenario. System administrators should prioritize applying the patched kernel versions as soon as possible, particularly in environments running ocfs2 filesystems where extended attribute operations are common. Monitoring for kernel panic messages related to NULL pointer dereferences in ocfs2 subsystems should be implemented as part of security operations. Organizations should also consider implementing additional kernel hardening measures such as kernel page table isolation and control flow integrity checks to reduce the attack surface for similar memory safety vulnerabilities. The fix aligns with the principle of defensive programming by ensuring proper state management and preventing double-free conditions that are common in kernel memory management operations.