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Jiayuan Chen 308e7e4d0a serial: caif: fix use-after-free in caif_serial ldisc_close()
There is a use-after-free bug in caif_serial where handle_tx() may
access ser->tty after the tty has been freed.

The race condition occurs between ldisc_close() and packet transmission:

    CPU 0 (close)                     CPU 1 (xmit)
    -------------                     ------------
    ldisc_close()
      tty_kref_put(ser->tty)
      [tty may be freed here]
                     <-- race window -->
                                      caif_xmit()
                                        handle_tx()
                                          tty = ser->tty  // dangling ptr
                                          tty->ops->write() // UAF!
      schedule_work()
        ser_release()
          unregister_netdevice()

The root cause is that tty_kref_put() is called in ldisc_close() while
the network device is still active and can receive packets.

Since ser and tty have a 1:1 binding relationship with consistent
lifecycles (ser is allocated in ldisc_open and freed in ser_release
via unregister_netdevice, and each ser binds exactly one tty), we can
safely defer the tty reference release to ser_release() where the
network device is unregistered.

Fix this by moving tty_kref_put() from ldisc_close() to ser_release(),
after unregister_netdevice(). This ensures the tty reference is held
as long as the network device exists, preventing the UAF.

Note: We save ser->tty before unregister_netdevice() because ser is
embedded in netdev's private data and will be freed along with netdev
(needs_free_netdev = true).

How to reproduce: Add mdelay(500) at the beginning of ldisc_close()
to widen the race window, then run the reproducer program [1].

Note: There is a separate deadloop issue in handle_tx() when using
PORT_UNKNOWN serial ports (e.g., /dev/ttyS3 in QEMU without proper
serial backend). This deadloop exists even without this patch,
and is likely caused by inconsistency between uart_write_room() and
uart_write() in serial core. It has been addressed in a separate
patch [2].

KASAN report:

==================================================================
BUG: KASAN: slab-use-after-free in handle_tx+0x5d1/0x620
Read of size 1 at addr ffff8881131e1490 by task caif_uaf_trigge/9929

Call Trace:
 <TASK>
 dump_stack_lvl+0x10e/0x1f0
 print_report+0xd0/0x630
 kasan_report+0xe4/0x120
 handle_tx+0x5d1/0x620
 dev_hard_start_xmit+0x9d/0x6c0
 __dev_queue_xmit+0x6e2/0x4410
 packet_xmit+0x243/0x360
 packet_sendmsg+0x26cf/0x5500
 __sys_sendto+0x4a3/0x520
 __x64_sys_sendto+0xe0/0x1c0
 do_syscall_64+0xc9/0xf80
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f615df2c0d7

Allocated by task 9930:

Freed by task 64:

Last potentially related work creation:

The buggy address belongs to the object at ffff8881131e1000
 which belongs to the cache kmalloc-cg-2k of size 2048
The buggy address is located 1168 bytes inside of
 freed 2048-byte region [ffff8881131e1000, ffff8881131e1800)

The buggy address belongs to the physical page:
page_owner tracks the page as allocated
page last free pid 9778 tgid 9778 stack trace:

Memory state around the buggy address:
 ffff8881131e1380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8881131e1400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8881131e1480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                         ^
 ffff8881131e1500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8881131e1580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
[1]: https://gist.github.com/mrpre/f683f244544f7b11e7fa87df9e6c2eeb
[2]: https://lore.kernel.org/linux-serial/20260204074327.226165-1-jiayuan.chen@linux.dev/T/#u

Reported-by: syzbot+827272712bd6d12c79a4@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/000000000000a4a7550611e234f5@google.com/T/
Fixes: 56e0ef527b ("drivers/net: caif: fix wrong rtnl_is_locked() usage")
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jiayuan Chen <jiayuan.chen@shopee.com>
Reviewed-by: Jijie Shao <shaojijie@huawei.com>
Link: https://patch.msgid.link/20260206074450.154267-1-jiayuan.chen@linux.dev
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
2026-02-10 15:23:11 +01:00
arch 5 hotfixes. 2 are cc:stable, 2 are for MM. 2026-02-04 16:04:00 -08:00
block block-6.19-20260122 2026-01-23 12:53:56 -08:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: authencesn - reject too-short AAD (assoclen<8) to match ESP/ESN spec 2026-01-20 14:38:48 +08:00
Documentation mptcp: fix kdoc warnings 2026-02-06 20:35:06 -08:00
drivers serial: caif: fix use-after-free in caif_serial ldisc_close() 2026-02-10 15:23:11 +01:00
fs two client memory leak fixes 2026-02-03 16:20:59 -08:00
include mptcp: fix kdoc warnings 2026-02-06 20:35:06 -08:00
init Significant patch series in this pull request: 2025-12-06 14:01:20 -08:00
io_uring io_uring-6.19-20260122 2026-01-23 12:51:00 -08:00
ipc Significant patch series in this pull request: 2025-12-06 14:01:20 -08:00
kernel 5 hotfixes. 2 are cc:stable, 2 are for MM. 2026-02-04 16:04:00 -08:00
lib mm/zone_device: reinitialize large zone device private folios 2026-01-26 19:03:48 -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 5 hotfixes. 2 are cc:stable, 2 are for MM. 2026-02-04 16:04:00 -08:00
net xfrm: fix ip_rt_bug race in icmp_route_lookup reverse path 2026-02-10 15:06:11 +01:00
rust Rust fixes for v6.19 2026-01-30 16:15:59 -08:00
samples samples/ftrace: Adjust LoongArch register restore order in direct calls 2025-12-31 15:19:25 +08:00
scripts Miscellaneous objtool fixes: 2026-02-01 10:27:43 -08:00
security lsm: preserve /proc/sys/vm/mmap_min_addr when !CONFIG_SECURITY 2026-01-29 13:56:53 -05:00
sound ASoC: Fixes for v6.19 2026-01-29 13:58:06 +01:00
tools selftests: mptcp: connect: fix maybe-uninitialize warn 2026-02-06 20:35:07 -08:00
usr initramfs: add gen_init_cpio to hostprogs unconditionally 2025-11-26 21:55:40 +01:00
virt KVM: Don't clobber irqfd routing type when deassigning irqfd 2026-01-14 13:17:14 -08:00
.clang-format s390/pci: Fix cyclic dead-lock in zpci_zdev_put() and zpci_scan_devices() 2025-12-14 11:03:58 +01:00
.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: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.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 5 hotfixes. 2 are cc:stable, 2 are for MM. 2026-02-04 16:04:00 -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 nfc: MAINTAINERS: Orphan the NFC and look for new maintainers 2026-01-20 16:05:38 -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 Including fixes from wireless and Netfilter. 2026-02-05 09:39:26 -08:00
Makefile Linux 6.19-rc8 2026-02-01 14:01:13 -08:00
README README: restructure with role-based documentation and guidelines 2025-11-29 08:40:33 -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


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



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