---
id: CVE-2026-98539
title: >-
  fs/ntfs3: use d_instantiate_new() in ntfs_create_inode() and murder syzbot's
  "WARNING in do_new_mount" saga
summary: >-
  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(…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 82cae269cfa953032fbb8980a7d554d60fb00b17 <
    6fda7121cb6a8ea6fbd77d0f787f04b8e8b5358e
  - >-
    Linux >= 82cae269cfa953032fbb8980a7d554d60fb00b17 <
    37ec7353f4ac495b28284b0fcb0e53d21d1b3f3f
  - >-
    Linux >= 82cae269cfa953032fbb8980a7d554d60fb00b17 <
    1ae2a242c15b03470b1b16289298e597bbe3bb29
  - >-
    Linux >= 82cae269cfa953032fbb8980a7d554d60fb00b17 <
    1abd643f3783ea8f8e273c18697ff0413aa92dc7
  - Linux 5.15
published: '2026-10-18'
updated: '2026-10-18'
sourceUpdated: '2026-10-18T15:18:06.921Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-98539'
references:
  - url: 'https://git.kernel.org/stable/c/6fda7121cb6a8ea6fbd77d0f787f04b8e8b5358e'
  - url: 'https://git.kernel.org/stable/c/37ec7353f4ac495b28284b0fcb0e53d21d1b3f3f'
  - url: 'https://git.kernel.org/stable/c/1ae2a242c15b03470b1b16289298e597bbe3bb29'
  - url: 'https://git.kernel.org/stable/c/1abd643f3783ea8f8e273c18697ff0413aa92dc7'
tags:
  - cve.org
ingestedAt: '2026-10-18T15:45:12.277Z'
---

## Overview

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.

## Affected

- `Linux >= 82cae269cfa953032fbb8980a7d554d60fb00b17 < 6fda7121cb6a8ea6fbd77d0f787f04b8e8b5358e`
- `Linux >= 82cae269cfa953032fbb8980a7d554d60fb00b17 < 37ec7353f4ac495b28284b0fcb0e53d21d1b3f3f`
- `Linux >= 82cae269cfa953032fbb8980a7d554d60fb00b17 < 1ae2a242c15b03470b1b16289298e597bbe3bb29`
- `Linux >= 82cae269cfa953032fbb8980a7d554d60fb00b17 < 1abd643f3783ea8f8e273c18697ff0413aa92dc7`
- `Linux 5.15`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.