CVE-2026-72162 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
ocfs2: fix UBSAN array-index-out-of-bounds in ocfs2_sum_rightmost_rec
[BUG]
On-disk corruption setting l_next_free_rec to 0 in an inode's embedded extent list triggers a UBSAN panic on the next write to that file.
[CAUSE]
ocfs2_sum_rightmost_rec() computes i = le16_to_cpu(el->l_next_free_rec) - 1 and accesses el->l_recs[i] without validating i. When l_next_free_rec
is 0, i becomes -1; when l_next_free_rec exceeds l_count, i falls past the end of the array. Either case violates the __counted_by_le(l_count) annotation on l_recs[] and triggers UBSAN.
[FIX]
Validate the inode's embedded extent list when the inode is read, in ocfs2_validate_inode_block(): l_count must be non-zero and no larger than the inode block can hold, and l_next_free_rec must not exceed l_count. A corrupt list is rejected at read time, before the b-tree code can index l_recs[] out of bounds.
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Analysis
by VulDB Data Team • 08/15/2026
The vulnerability described represents a critical array index out-of-bounds access flaw in the ocfs2 file system implementation within the Linux kernel. This issue manifests when an on-disk corruption condition occurs where the l_next_free_rec field in an inode's embedded extent list is set to zero, subsequently triggering a UBSAN (Undefined Behavior Sanitizer) panic during subsequent write operations to that file. The root cause lies in the ocfs2_sum_rightmost_rec() function which performs a calculation without proper bounds validation, creating a dangerous scenario where memory access occurs beyond the legitimate array boundaries.
The technical flaw specifically involves integer underflow and array boundary violations within the extent list handling code of the ocfs2 file system driver. When the function computes i = le16_to_cpu(el->l_next_free_rec) - 1, it assumes that l_next_free_rec will always be greater than zero, but when this field is corrupted to zero, the resulting value becomes negative one, leading to invalid memory access. Additionally, when l_next_free_rec exceeds the legitimate l_count value, the computed index i extends beyond the array bounds, both scenarios violating the documented __counted_by_le(l_count) annotation that establishes the legitimate range for l_recs[] array access. This pattern aligns with CWE-129, which addresses improper validation of array indices, and represents a classic example of unchecked array access vulnerability.
The operational impact of this vulnerability is severe as it can lead to system instability through kernel panics and potential data corruption scenarios. The UBSAN panic occurs during write operations, effectively blocking further file modifications and potentially causing denial of service conditions for applications accessing affected files. The vulnerability demonstrates how seemingly minor corruption in metadata structures can escalate into critical system failures, particularly when the file system code fails to validate input data before processing. From an ATT&CK perspective, this represents a privilege escalation vector through kernel memory corruption techniques that can be leveraged to destabilize system operations and potentially enable further exploitation.
The proposed fix implements proactive validation during inode read operations within ocfs2_validate_inode_block() function, addressing the issue at the point of data ingress rather than during problematic processing. This approach ensures that corrupted extent lists are rejected before they can be processed by subsequent functions, preventing the out-of-bounds access conditions from occurring. The validation checks establish that l_count must be non-zero and within reasonable limits for the inode block capacity, while also ensuring that l_next_free_rec does not exceed l_count values. This defensive programming approach prevents the propagation of corrupt data through the system and aligns with secure coding practices recommended in industry standards for preventing buffer overflows and memory safety issues in kernel space code.