# CVE-2026-89723

## Summary

- **CVE ID:** CVE-2026-89723
- **Severity:** HIGH
- **CVSS Score:** 7.8 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H)
- **CWE:** N/A
- **Published:** Sep 11, 2026
- **Last Modified:** Sep 14, 2026

## Description

In the Linux kernel, the following vulnerability has been resolved:

nilfs2: fix slab-out-of-bounds in nilfs_direct_propagate after truncation

Shuangpeng Bai reported that KASAN detected a slab-out-of-bounds error
in nilfs_direct_propagate() during testing.

Analysis revealed that after truncating a file, a node block immediately
below the B-tree root was not deleted.  Instead, it remained in the B-tree
node cache in a dirty state.  The log writer subsequently detected this
block and incorrectly invoked nilfs_direct_propagate() on it, which is
designed to handle only data blocks in direct mapping.

B-tree nodes in the cache are managed by virtual block numbers, and their
logical keys typically exceed the range expected by direct mapping.
Consequently, processing such a node as a direct mapping entry triggers
a slab-out-of-bounds access.

The root cause is that when a B-tree mapping collapses into a direct
mapping during truncation, an intermediate node block pointed to by the
root node is left behind as garbage instead of being explicitly deleted.

This resolves the issue by adding a nilfs_btree_discard() operation
to delete the remaining intermediate node block during the conversion.
A 'deform' flag is added to the bop_delete interface to explicitly signal
that the deletion is part of a mapping transformation.  This allows the
B-tree mapping implementation to perform the necessary cleanup and
discarding of the residual node structure that would be otherwise be left
orphaned after the transition.

## Affected Products

- Linux — Linux (36a580eb489f54d81a0534974962e732a314b999)
- Linux — Linux (2.6.30)
- Linux — Linux (0)
- Linux — Linux (6.12.109)
- Linux — Linux (6.18.50)
- Linux — Linux (7.2.4)
- Linux — Linux (7.3-rc1)
- Linux — Linux (5.10.270)
- Linux — Linux (5.15.221)
- Linux — Linux (6.1.188)
- Linux — Linux (6.6.157)

## References

- [CNA](https://git.kernel.org/stable/c/5d3783c451a546373662ee11ec17019273e68034)
- [CNA](https://git.kernel.org/stable/c/448636c745a3f3b8582a0b8ce718c890a11c0fa9)
- [CNA](https://git.kernel.org/stable/c/28362e8ce51377afdec1782e661e808328a10514)
- [CNA](https://git.kernel.org/stable/c/45662dedb8f272ef7f16e69f13424c4bd0399240)
- [CNA](https://git.kernel.org/stable/c/39005fd1ce654ffdecacddc406b9a038efe606e6)
- [CNA](https://git.kernel.org/stable/c/bf49e6f6ddc12445a0330708b365de6458085980)
- [CNA](https://git.kernel.org/stable/c/4a1bb1f9f24a935c9b3f4fbf98012fa6d4ad826d)
- [CNA](https://git.kernel.org/stable/c/b313edfbc0c2a60f7ce09b2e81ee71909ab8ddaf)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.16%
- **EPSS Percentile:** 6.0

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-17._