Cen Zhang 81fe702ff1 ntfs: avoid stale runlist element dereference in MFT writeback
ntfs_write_mft_block() maps each $MFT record through the $MFT data
runlist. For sub-folio clusters it looks up a struct runlist_element under
ni->runlist.lock, drops the lock, and later uses rl->length and rl->vcn
when choosing folio_sz.

That pointer is only borrowed from ni->runlist.rl. Concurrent $MFT
allocation extension can merge a replacement runlist under the same lock,
and ntfs_rl_realloc() can free the old backing array. If that happens
between the lookup and the later folio_sz decision, writeback can
dereference freed runlist storage.

The buggy scenario involves two paths, with each column showing the order
within that path:

MFT writeback path:               $MFT allocation extension:
1. Look up rl under               1. Extend the $MFT data allocation.
   ni->runlist.lock.              2. Publish a replacement runlist.
2. Drop ni->runlist.lock.         3. Free the old runlist array.
3. Read rl->length and rl->vcn
   to choose folio_sz.

Compute the remaining run length while ni->runlist.lock is still held, and
use that scalar after unlock. This preserves the existing folio sizing
decision without carrying a borrowed runlist_element across the lock
boundary.

Validation reproduced this kernel report:
BUG: KASAN: slab-use-after-free in ntfs_mft_writepages+0x1c8d/0x1fb0

Call Trace:
 <TASK>
 dump_stack_lvl+0x66/0xa0
 print_report+0xce/0x630
 ? ntfs_mft_writepages+0x1c8d/0x1fb0
 ? srso_alias_return_thunk+0x5/0xfbef5
 ? __virt_addr_valid+0x20d/0x410
 ? ntfs_mft_writepages+0x1c8d/0x1fb0
 kasan_report+0xe0/0x110
 ? ntfs_mft_writepages+0x1c8d/0x1fb0
 ntfs_mft_writepages+0x1c8d/0x1fb0
 ? __pfx_ntfs_mft_writepages+0x10/0x10
 ? __pfx___mutex_unlock_slowpath+0x10/0x10
 ? srso_alias_return_thunk+0x5/0xfbef5
 ? iput+0x92/0xa80
 do_writepages+0x219/0x530
 ? __pfx_do_writepages+0x10/0x10
 __writeback_single_inode+0x117/0xf50
 ? do_raw_spin_lock+0x130/0x270
 ? __pfx_do_raw_spin_lock+0x10/0x10
 ? __pfx___writeback_single_inode+0x10/0x10
 ? srso_alias_return_thunk+0x5/0xfbef5
 writeback_sb_inodes+0x65b/0x1810
 ? srso_alias_return_thunk+0x5/0xfbef5
 ? lock_acquire+0x2b8/0x2f0
 ? __pfx_writeback_sb_inodes+0x10/0x10
 ? lock_release+0x1e0/0x280
 ? _raw_spin_unlock+0x23/0x40
 ? move_expired_inodes+0x2b8/0x850
 __writeback_inodes_wb+0xf4/0x270
 ? __pfx___writeback_inodes_wb+0x10/0x10
 ? srso_alias_return_thunk+0x5/0xfbef5
 ? queue_io+0x2e4/0x410
 wb_writeback+0x666/0x880
 ? srso_alias_return_thunk+0x5/0xfbef5
 ? __pfx_wb_writeback+0x10/0x10
 ? srso_alias_return_thunk+0x5/0xfbef5
 ? srso_alias_return_thunk+0x5/0xfbef5
 ? get_nr_dirty_inodes+0x1c/0x170
 wb_workfn+0x75e/0xbb0
 ? srso_alias_return_thunk+0x5/0xfbef5
 ? _raw_spin_unlock_irqrestore+0x27/0x60
 ? __pfx_wb_workfn+0x10/0x10
 ? __pfx_debug_object_deactivate+0x10/0x10
 ? lock_acquire+0x2b8/0x2f0
 ? srso_alias_return_thunk+0x5/0xfbef5
 ? lock_release+0x1e0/0x280
 process_one_work+0x8d0/0x1870
 ? __pfx_process_one_work+0x10/0x10
 ? srso_alias_return_thunk+0x5/0xfbef5
 worker_thread+0x575/0xf80
 ? __pfx_worker_thread+0x10/0x10
 kthread+0x2e7/0x3c0
 ? __pfx_kthread+0x10/0x10
 ret_from_fork+0x576/0x810
 ? __pfx_ret_from_fork+0x10/0x10
 ? srso_alias_return_thunk+0x5/0xfbef5
 ? __switch_to+0x57e/0xe10
 ? __switch_to_asm+0x33/0x70
 ? __pfx_kthread+0x10/0x10
 ret_from_fork_asm+0x1a/0x30
 </TASK>

Allocated by task 970:
 kasan_save_stack+0x33/0x60
 kasan_save_track+0x14/0x30
 __kasan_kmalloc+0xaa/0xb0
 __kvmalloc_node_noprof+0x353/0x920
 ntfs_rl_realloc+0x3c/0x80
 ntfs_runlists_merge+0x1212/0x3010
 ntfs_mft_data_extend_allocation_nolock+0x3e0/0x1f40
 ntfs_mft_record_alloc+0x1ab4/0x4f10
 __ntfs_create+0x680/0x2e50
 ntfs_create+0x1e6/0x3a0
 path_openat+0x2b55/0x3c10
 do_file_open+0x1f4/0x460
 do_sys_openat2+0xde/0x170
 __x64_sys_openat+0x122/0x1e0
 do_syscall_64+0x115/0x6a0
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 1294:
 kasan_save_stack+0x33/0x60
 kasan_save_track+0x14/0x30
 kasan_save_free_info+0x3b/0x60
 __kasan_slab_free+0x5f/0x80
 kfree+0x307/0x580
 ntfs_rl_realloc+0x66/0x80
 ntfs_runlists_merge+0x1212/0x3010
 ntfs_mft_data_extend_allocation_nolock+0x3e0/0x1f40
 ntfs_mft_record_alloc+0x1ab4/0x4f10
 __ntfs_create+0x680/0x2e50
 ntfs_create+0x1e6/0x3a0
 path_openat+0x2b55/0x3c10
 do_file_open+0x1f4/0x460
 do_sys_openat2+0xde/0x170
 __x64_sys_openat+0x122/0x1e0
 do_syscall_64+0x115/0x6a0
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Fixes: 115380f9a2 ("ntfs: update mft operations")
Assisted-by: Codex:gpt-5.5
Signed-off-by: Cen Zhang <zzzccc427@gmail.com>
Reviewed-by: Hyunchul Lee <hyc.lee@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
2026-06-25 23:12:02 +09:00
2026-01-26 19:07:09 -08:00
2022-09-28 09:02:20 +02:00
2025-02-19 14:53:27 -07:00

Linux kernel
============

The Linux kernel is the core of any Linux operating system. It manages hardware,
system resources, and provides the fundamental services for all other software.

Quick Start
-----------

* Report a bug: See Documentation/admin-guide/reporting-issues.rst
* Get the latest kernel: https://kernel.org
* Build the kernel: See Documentation/admin-guide/quickly-build-trimmed-linux.rst
* Join the community: https://lore.kernel.org/

Essential Documentation
-----------------------

All users should be familiar with:

* Building requirements: Documentation/process/changes.rst
* Code of Conduct: Documentation/process/code-of-conduct.rst
* License: See COPYING

Documentation can be built with make htmldocs or viewed online at:
https://www.kernel.org/doc/html/latest/


Who Are You?
============

Find your role below:

* New Kernel Developer - Getting started with kernel development
* Academic Researcher - Studying kernel internals and architecture
* Security Expert - Hardening and vulnerability analysis
* Backport/Maintenance Engineer - Maintaining stable kernels
* System Administrator - Configuring and troubleshooting
* Maintainer - Leading subsystems and reviewing patches
* Hardware Vendor - Writing drivers for new hardware
* Distribution Maintainer - Packaging kernels for distros
* AI Coding Assistant - LLMs and AI-powered development tools


For Specific Users
==================

New Kernel Developer
--------------------

Welcome! Start your kernel development journey here:

* Getting Started: Documentation/process/development-process.rst
* Your First Patch: Documentation/process/submitting-patches.rst
* Coding Style: Documentation/process/coding-style.rst
* Build System: Documentation/kbuild/index.rst
* Development Tools: Documentation/dev-tools/index.rst
* Kernel Hacking Guide: Documentation/kernel-hacking/hacking.rst
* Core APIs: Documentation/core-api/index.rst

Academic Researcher
-------------------

Explore the kernel's architecture and internals:

* Researcher Guidelines: Documentation/process/researcher-guidelines.rst
* Memory Management: Documentation/mm/index.rst
* Scheduler: Documentation/scheduler/index.rst
* Networking Stack: Documentation/networking/index.rst
* Filesystems: Documentation/filesystems/index.rst
* RCU (Read-Copy Update): Documentation/RCU/index.rst
* Locking Primitives: Documentation/locking/index.rst
* Power Management: Documentation/power/index.rst

Security Expert
---------------

Security documentation and hardening guides:

* Security Documentation: Documentation/security/index.rst
* LSM Development: Documentation/security/lsm-development.rst
* Self Protection: Documentation/security/self-protection.rst
* Reporting Vulnerabilities: Documentation/process/security-bugs.rst
* CVE Procedures: Documentation/process/cve.rst
* Embargoed Hardware Issues: Documentation/process/embargoed-hardware-issues.rst
* Security Features: Documentation/userspace-api/seccomp_filter.rst

Backport/Maintenance Engineer
-----------------------------

Maintain and stabilize kernel versions:

* Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst
* Backporting Guide: Documentation/process/backporting.rst
* Applying Patches: Documentation/process/applying-patches.rst
* Subsystem Profile: Documentation/maintainer/maintainer-entry-profile.rst
* Git for Maintainers: Documentation/maintainer/configure-git.rst

System Administrator
--------------------

Configure, tune, and troubleshoot Linux systems:

* Admin Guide: Documentation/admin-guide/index.rst
* Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst
* Sysctl Tuning: Documentation/admin-guide/sysctl/index.rst
* Tracing/Debugging: Documentation/trace/index.rst
* Performance Security: Documentation/admin-guide/perf-security.rst
* Hardware Monitoring: Documentation/hwmon/index.rst

Maintainer
----------

Lead kernel subsystems and manage contributions:

* Maintainer Handbook: Documentation/maintainer/index.rst
* Pull Requests: Documentation/maintainer/pull-requests.rst
* Managing Patches: Documentation/maintainer/modifying-patches.rst
* Rebasing and Merging: Documentation/maintainer/rebasing-and-merging.rst
* Development Process: Documentation/process/maintainer-handbooks.rst
* Maintainer Entry Profile: Documentation/maintainer/maintainer-entry-profile.rst
* Git Configuration: Documentation/maintainer/configure-git.rst

Hardware Vendor
---------------

Write drivers and support new hardware:

* Driver API Guide: Documentation/driver-api/index.rst
* Driver Model: Documentation/driver-api/driver-model/driver.rst
* Device Drivers: Documentation/driver-api/infrastructure.rst
* Bus Types: Documentation/driver-api/driver-model/bus.rst
* Device Tree Bindings: Documentation/devicetree/bindings/
* Power Management: Documentation/driver-api/pm/index.rst
* DMA API: Documentation/core-api/dma-api.rst

Distribution Maintainer
-----------------------

Package and distribute the kernel:

* Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst
* ABI Documentation: Documentation/ABI/README
* Kernel Configuration: Documentation/kbuild/kconfig.rst
* Module Signing: Documentation/admin-guide/module-signing.rst
* Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst
* Tainted Kernels: Documentation/admin-guide/tainted-kernels.rst

AI Coding Assistant
-------------------

CRITICAL: If you are an LLM or AI-powered coding assistant, you MUST read and
follow the AI coding assistants documentation before contributing to the Linux
kernel:

* Documentation/process/coding-assistants.rst

This documentation contains essential requirements about licensing, attribution,
and the Developer Certificate of Origin that all AI tools must comply with.


Communication and Support
=========================

* Mailing Lists: https://lore.kernel.org/
* IRC: #kernelnewbies on irc.oftc.net
* Bugzilla: https://bugzilla.kernel.org/
* MAINTAINERS file: Lists subsystem maintainers and mailing lists
* Email Clients: Documentation/process/email-clients.rst
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