# CVE-2026-98539: fs/ntfs3: use d_instantiate_new() in ntfs_create_inode() and murder syzbot's "WARNING in do_new_mount" saga

> A race condition in the Linux kernel NTFS3 driver allows local attackers to trigger a kernel warning and potential denial of service via concurrent mount and directory creation operations.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 18 Oct 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-109007, BELL-CVE-2026-98539, DEBIAN-CVE-2026-98539, GHSA-fgm8-xgjp-8vhv, UBUNTU-CVE-2026-98539

## What is CVE-2026-98539?

CVE-2026-98539 is a vulnerability in Linux, published on 18 Oct 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

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

fs/ntfs3: use d_instantiate_new() in ntfs_create_inode() and murder syzbot's "WARNING in do_new_mount" saga

ntfs_create_inode() creates a new inode via ntfs_new_inode(). It hashes
it with insert_inode_locked() and so it's marked as I_NEW until
unlock_new_inode().

ntfs 3 calls d_instantiate() in between though... Since the dentry was
already hashed by the lookup before the create any path walk finds it
without touching the parent's i_rwsem and so can lock the inode.

If the inode is a directory unlock_new_inode() calls
lockdep_annotate_inode_mutex_key() and marks i_rwsem with the
i_mutex_dir_key class.

That resets the count and the owner of a lock somebody else may already
hold by now...

syzbot has been spamming us with the same godforsaken bug

  "WARNING in do_new_mount"

since 2023. I can't take it anymore so I went looking. Afaict, syzbot's
executor chdirs into a freshly mounted ntfs3 image, creates a
directory and then mounts some pseudofs on it. Everytime the mkdir()
takes longer than syzbot waits mount() runs concurrently:

  mkdir("./sys")                        mount(NULL, "./sys", "sysfs")
  ntfs_create_inode()
    d_instantiate()
                                        user_path_at() finds the dentry
                                        do_lock_mount()
                                          inode_lock(inode)
                                          namespace_lock()
    unlock_new_inode()
      lockdep_annotate_inode_mutex_key()
        init_rwsem(&inode->i_rwsem)
                                        unlock_mount()
                                          inode_unlock(inode)

The mount side then releases a lock that according to the rwsem nobody
holds:

  DEBUG_RWSEMS_WARN_ON((rwsem_owner(sem) != current) && ...):
  count = 0x0, magic = 0xffff888043a854e8, owner = 0x0,
  curr 0xffff888000244880, list empty
  WARNING: CPU: 0 PID: 5346 at kernel/locking/rwsem.c:1368 __up_write
  Call Trace:
   inode_unlock include/linux/fs.h:877 [inline]
   unlock_mount fs/namespace.c:2892 [inline]
   do_new_mount_fc fs/namespace.c:3828 [inline]
   do_new_mount+0x777/0xa40 fs/namespace.c:3887

On PREEMPT_RT the same thing shows up as

  DEBUG_LOCKS_WARN_ON(rt_mutex_owner(lock) != current)
  WARNING: kernel/locking/rtmutex_common.h:193 at rt_mutex_slowunlock

The up_write() underflows the reset count. A following inode_lock() on
that directory then never returns. A path walk into the new directory
racing with the mkdir() corrupts the lock the same way via
inode_lock_shared() in lookup_slow().

Switch to d_instantiate_new() and drop the trailing unlock_new_inode().
All error paths bail out before that point with I_NEW still set and
keep using discard_new_inode().

May we never see this fscking bug report again.

## Which versions are affected by CVE-2026-98539?


## How do I fix CVE-2026-98539?

Apply the vendor's patch.

## Is CVE-2026-98539 being exploited?

There is no known exploitation of CVE-2026-98539 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98539 and fix it if it is affected.

What it is: CVE-2026-98539 is a vulnerability in Linux, published on 18 Oct 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-98539 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-98539/ (Markdown: https://insights.sbomify.com/CVE-2026-98539/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98539
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98539
- OSV: https://osv.dev/vulnerability/CVE-2026-98539

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98539/
Summaries are generated and may contain mistakes; the official description above is the record.