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Duoming Zhou bae8a5d2e7 net: wan: farsync: Fix use-after-free bugs caused by unfinished tasklets
When the FarSync T-series card is being detached, the fst_card_info is
deallocated in fst_remove_one(). However, the fst_tx_task or fst_int_task
may still be running or pending, leading to use-after-free bugs when the
already freed fst_card_info is accessed in fst_process_tx_work_q() or
fst_process_int_work_q().

A typical race condition is depicted below:

CPU 0 (cleanup)           | CPU 1 (tasklet)
                          | fst_start_xmit()
fst_remove_one()          |   tasklet_schedule()
  unregister_hdlc_device()|
                          | fst_process_tx_work_q() //handler
  kfree(card) //free      |   do_bottom_half_tx()
                          |     card-> //use

The following KASAN trace was captured:

==================================================================
 BUG: KASAN: slab-use-after-free in do_bottom_half_tx+0xb88/0xd00
 Read of size 4 at addr ffff88800aad101c by task ksoftirqd/3/32
 ...
 Call Trace:
  <IRQ>
  dump_stack_lvl+0x55/0x70
  print_report+0xcb/0x5d0
  ? do_bottom_half_tx+0xb88/0xd00
  kasan_report+0xb8/0xf0
  ? do_bottom_half_tx+0xb88/0xd00
  do_bottom_half_tx+0xb88/0xd00
  ? _raw_spin_lock_irqsave+0x85/0xe0
  ? __pfx__raw_spin_lock_irqsave+0x10/0x10
  ? __pfx___hrtimer_run_queues+0x10/0x10
  fst_process_tx_work_q+0x67/0x90
  tasklet_action_common+0x1fa/0x720
  ? hrtimer_interrupt+0x31f/0x780
  handle_softirqs+0x176/0x530
  __irq_exit_rcu+0xab/0xe0
  sysvec_apic_timer_interrupt+0x70/0x80
 ...

 Allocated by task 41 on cpu 3 at 72.330843s:
  kasan_save_stack+0x24/0x50
  kasan_save_track+0x17/0x60
  __kasan_kmalloc+0x7f/0x90
  fst_add_one+0x1a5/0x1cd0
  local_pci_probe+0xdd/0x190
  pci_device_probe+0x341/0x480
  really_probe+0x1c6/0x6a0
  __driver_probe_device+0x248/0x310
  driver_probe_device+0x48/0x210
  __device_attach_driver+0x160/0x320
  bus_for_each_drv+0x101/0x190
  __device_attach+0x198/0x3a0
  device_initial_probe+0x78/0xa0
  pci_bus_add_device+0x81/0xc0
  pci_bus_add_devices+0x7e/0x190
  enable_slot+0x9b9/0x1130
  acpiphp_check_bridge.part.0+0x2e1/0x460
  acpiphp_hotplug_notify+0x36c/0x3c0
  acpi_device_hotplug+0x203/0xb10
  acpi_hotplug_work_fn+0x59/0x80
 ...

 Freed by task 41 on cpu 1 at 75.138639s:
  kasan_save_stack+0x24/0x50
  kasan_save_track+0x17/0x60
  kasan_save_free_info+0x3b/0x60
  __kasan_slab_free+0x43/0x70
  kfree+0x135/0x410
  fst_remove_one+0x2ca/0x540
  pci_device_remove+0xa6/0x1d0
  device_release_driver_internal+0x364/0x530
  pci_stop_bus_device+0x105/0x150
  pci_stop_and_remove_bus_device+0xd/0x20
  disable_slot+0x116/0x260
  acpiphp_disable_and_eject_slot+0x4b/0x190
  acpiphp_hotplug_notify+0x230/0x3c0
  acpi_device_hotplug+0x203/0xb10
  acpi_hotplug_work_fn+0x59/0x80
 ...

 The buggy address belongs to the object at ffff88800aad1000
  which belongs to the cache kmalloc-1k of size 1024
 The buggy address is located 28 bytes inside of
  freed 1024-byte region
 The buggy address belongs to the physical page:
 page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0xaad0
 head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
 flags: 0x100000000000040(head|node=0|zone=1)
 page_type: f5(slab)
 raw: 0100000000000040 ffff888007042dc0 dead000000000122 0000000000000000
 raw: 0000000000000000 0000000080100010 00000000f5000000 0000000000000000
 head: 0100000000000040 ffff888007042dc0 dead000000000122 0000000000000000
 head: 0000000000000000 0000000080100010 00000000f5000000 0000000000000000
 head: 0100000000000003 ffffea00002ab401 00000000ffffffff 00000000ffffffff
 head: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
 page dumped because: kasan: bad access detected

 Memory state around the buggy address:
  ffff88800aad0f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
  ffff88800aad0f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 >ffff88800aad1000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                             ^
  ffff88800aad1080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
  ffff88800aad1100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ==================================================================

Fix this by ensuring that both fst_tx_task and fst_int_task are properly
canceled before the fst_card_info is released. Add tasklet_kill() in
fst_remove_one() to synchronize with any pending or running tasklets.
Since unregister_hdlc_device() stops data transmission and reception,
and fst_disable_intr() prevents further interrupts, it is appropriate
to place tasklet_kill() after these calls.

The bugs were identified through static analysis. To reproduce the issue
and validate the fix, a FarSync T-series card was simulated in QEMU and
delays(e.g., mdelay()) were introduced within the tasklet handler to
increase the likelihood of triggering the race condition.

Fixes: 2f623aaf9f ("net: farsync: Fix kmemleak when rmmods farsync")
Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
Reviewed-by: Jijie Shao <shaojijie@huawei.com>
Link: https://patch.msgid.link/20260219124637.72578-1-duoming@zju.edu.cn
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
2026-02-24 10:31:52 +01:00
arch bpf-fixes 2026-02-19 10:36:54 -08:00
block block-7.0-20260216 2026-02-17 08:48:45 -08:00
certs mm.git review status for linus..mm-nonmm-stable 2026-02-12 12:13:01 -08:00
crypto mm.git review status for linus..mm-nonmm-stable 2026-02-12 12:13:01 -08:00
Documentation Including fixes from Netfilter. 2026-02-19 10:39:08 -08:00
drivers net: wan: farsync: Fix use-after-free bugs caused by unfinished tasklets 2026-02-24 10:31:52 +01:00
fs mm.git review status for linus..mm-stable 2026-02-18 20:50:32 -08:00
include tcp: fix potential race in tcp_v6_syn_recv_sock() 2026-02-19 14:02:19 -08:00
init mm.git review status for linus..mm-nonmm-stable 2026-02-12 12:13:01 -08:00
io_uring io_uring-7.0-20260216 2026-02-17 08:33:49 -08:00
ipc mm.git review status for linus..mm-stable 2026-02-18 20:50:32 -08:00
kernel bpf-fixes 2026-02-19 10:36:54 -08:00
lib mm.git review status for linus..mm-nonmm-stable 2026-02-18 21:40:16 -08:00
LICENSES LICENSES: Add modern form of the LGPL-2.1 tags to the usage guide section 2025-10-22 07:58:19 +02:00
mm mm.git review status for linus..mm-stable 2026-02-18 20:50:32 -08:00
net net/rds: fix recursive lock in rds_tcp_conn_slots_available 2026-02-24 10:11:04 +01:00
rust USB / Thunderbolt changes for 7.0-rc1 2026-02-17 09:36:43 -08:00
samples USB / Thunderbolt changes for 7.0-rc1 2026-02-17 09:36:43 -08:00
scripts mm.git review status for linus..mm-nonmm-stable 2026-02-18 21:40:16 -08:00
security mm.git review status for linus..mm-stable 2026-02-18 20:50:32 -08:00
sound soundwire updates for 7.0 2026-02-17 10:07:13 -08:00
tools selftests: drv-net: rss_ctx: test RSS contexts persist after ifdown/up 2026-02-20 16:34:47 -08:00
usr kbuild: uapi: drop dependency on CC_CAN_LINK 2026-01-16 15:02:11 -07:00
virt Merge tag 'kvm-x86-pmu-6.20' of https://github.com/kvm-x86/linux into HEAD 2026-02-11 12:45:40 -05:00
.clang-format Devicetree updates for v7.0: 2026-02-11 18:27:08 -08:00
.clippy.toml rust: clean Rust 1.88.0's warning about clippy::disallowed_macros configuration 2025-05-07 00:11:47 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig editorconfig: add rst extension 2026-01-26 19:07:09 -08:00
.get_maintainer.ignore MAINTAINERS: remove Alyssa Rosenzweig 2025-09-18 21:17:31 +02:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore rust: kbuild: add proc macro library support 2025-11-24 17:15:36 +01:00
.mailmap Landlock update for v7.0-rc1 2026-02-11 15:57:08 -08:00
.pylintrc docs: Move the python libraries to tools/lib/python 2025-11-18 09:22:40 -07:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS Networking changes for 7.0 2026-02-11 19:31:52 -08:00
Kbuild sched: Make migrate_{en,dis}able() inline 2025-09-25 09:57:16 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS MAINTAINERS: include all of framer under pef2256 2026-02-23 17:05:25 -08:00
Makefile First round of Kbuild fixes for 7.0 2026-02-18 14:59:55 -08:00
README docs: add AI Coding Assistants documentation 2026-01-06 14:55:06 -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