tipc: Fix use-after-free in tipc_conn_close()
CVE: CVE-2025-38464
Component: kernel
CWE: CWE-416
Severity: Moderate
CVSS v3: 7.5/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:H
Release date: 2025-07-25T00:00:00+00:00

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

tipc: Fix use-after-free in tipc_conn_close().

syzbot reported a null-ptr-deref in tipc_conn_close() during netns
dismantle. [0]

tipc_topsrv_stop() iterates tipc_net(net)->topsrv->conn_idr and calls
tipc_conn_close() for each tipc_conn.

The problem is that tipc_conn_close() is called after releasing the
IDR lock.

At the same time, there might be tipc_conn_recv_work() running and it
could call tipc_conn_close() for the same tipc_conn and release its
last ->kref.

Once we release the IDR lock in tipc_topsrv_stop(), there is no
guarantee that the tipc_conn is alive.

Let's hold the ref before releasing the lock and put the ref after
tipc_conn_close() in tipc_topsrv_stop().

[0]:
BUG: KASAN: use-after-free in tipc_conn_close+0x122/0x140 net/tipc/topsrv.c:165
Read of size 8 at addr ffff888099305a08 by task kworker/u4:3/435

CPU: 0 PID: 435 Comm: kworker/u4:3 Not tainted 4.19.204-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: netns cleanup_net
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1fc/0x2ef lib/dump_stack.c:118
 print_address_description.cold+0x54/0x219 mm/kasan/report.c:256
 kasan_report_error.cold+0x8a/0x1b9 mm/kasan/report.c:354
 kasan_report mm/kasan/report.c:412 [inline]
 __asan_report_load8_noabort+0x88/0x90 mm/kasan/report.c:433
 tipc_conn_close+0x122/0x140 net/tipc/topsrv.c:165
 tipc_topsrv_stop net/tipc/topsrv.c:701 [inline]
 tipc_topsrv_exit_net+0x27b/0x5c0 net/tipc/topsrv.c:722
 ops_exit_list+0xa5/0x150 net/core/net_namespace.c:153
 cleanup_net+0x3b4/0x8b0 net/core/net_namespace.c:553
 process_one_work+0x864/0x1570 kernel/workqueue.c:2153
 worker_thread+0x64c/0x1130 kernel/workqueue.c:2296
 kthread+0x33f/0x460 kernel/kthread.c:259
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415

Allocated by task 23:
 kmem_cache_alloc_trace+0x12f/0x380 mm/slab.c:3625
 kmalloc include/linux/slab.h:515 [inline]
 kzalloc include/linux/slab.h:709 [inline]
 tipc_conn_alloc+0x43/0x4f0 net/tipc/topsrv.c:192
 tipc_topsrv_accept+0x1b5/0x280 net/tipc/topsrv.c:470
 process_one_work+0x864/0x1570 kernel/workqueue.c:2153
 worker_thread+0x64c/0x1130 kernel/workqueue.c:2296
 kthread+0x33f/0x460 kernel/kthread.c:259
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415

Freed by task 23:
 __cache_free mm/slab.c:3503 [inline]
 kfree+0xcc/0x210 mm/slab.c:3822
 tipc_conn_kref_release net/tipc/topsrv.c:150 [inline]
 kref_put include/linux/kref.h:70 [inline]
 conn_put+0x2cd/0x3a0 net/tipc/topsrv.c:155
 process_one_work+0x864/0x1570 kernel/workqueue.c:2153
 worker_thread+0x64c/0x1130 kernel/workqueue.c:2296
 kthread+0x33f/0x460 kernel/kthread.c:259
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415

The buggy address belongs to the object at ffff888099305a00
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 8 bytes inside of
 512-byte region [ffff888099305a00, ffff888099305c00)
The buggy address belongs to the page:
page:ffffea000264c140 count:1 mapcount:0 mapping:ffff88813bff0940 index:0x0
flags: 0xfff00000000100(slab)
raw: 00fff00000000100 ffffea00028b6b88 ffffea0002cd2b08 ffff88813bff0940
raw: 0000000000000000 ffff888099305000 0000000100000006 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff888099305900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888099305980: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888099305a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                      ^
 ffff888099305a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888099305b00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

Statement: A Use-After-Free vulnerability was found in tipc_conn_close() in the TIPC subsystem during the cleanup of network namespaces. The race condition between tipc_topsrv_stop() and tipc_conn_recv_work() could result in accessing a freed tipc_conn structure, leading to kernel crash or potential memory corruption. The bug was triggered by syzbot and fixed by ensuring proper reference counting.

The most straightforward exploitation scenario is a local Denial of Service (DoS), where an unprivileged user with the ability to create user and network namespaces spawns TIPC connections and then triggers network namespace teardown, creating a race condition that causes a use-after-free in tipc_conn_close(). This reliably leads to a kernel panic.

A hypothetical future scenario involves local privilege escalation, if the attacker can win the race and reallocate the freed object in a controlled way (e.g., via kmalloc-512 slab reusage), leading to memory corruption or hijacking of kernel control flow.

Importantly, this can be triggered without root privileges if the system allows unprivileged creation of user and net namespaces, which is the case on many Linux distributions (/proc/sys/user/max_user_namespaces > 0 and kernel.unprivileged_userns_clone=1).
In such environments, a regular user can execute the TIPC socket creation, manipulate netns teardown, and provoke the race condition required for exploitation.

Remediation:
For details on how to apply this update, which includes the changes described in this advisory, refer to:

https://access.redhat.com/articles/11258

The system must be rebooted for this update to take effect.
For details on how to apply this update, which includes the changes described in this advisory, refer to:

https://access.redhat.com/articles/11258

The system must be rebooted for this update to take effect.
For details on how to apply this update, which includes the changes described in this advisory, refer to:

https://access.redhat.com/articles/11258

The system must be rebooted for this update to take effect.
For details on how to apply this update, which includes the changes described in this advisory, refer to:

https://access.redhat.com/articles/11258

The system must be rebooted for this update to take effect.
For details on how to apply this update, which includes the changes described in this advisory, refer to:

https://access.redhat.com/articles/11258

The system must be rebooted for this update to take effect.
For details on how to apply this update, which includes the changes described in this advisory, refer to:

https://access.redhat.com/articles/11258

The system must be rebooted for this update to take effect.
For details on how to apply this update, which includes the changes described in this advisory, refer to:

https://access.redhat.com/articles/11258

The system must be rebooted for this update to take effect.
For details on how to apply this update, which includes the changes described in this advisory, refer to:

https://access.redhat.com/articles/11258

The system must be rebooted for this update to take effect.
For details on how to apply this update, which includes the changes described in this advisory, refer to:

https://access.redhat.com/articles/11258

The system must be rebooted for this update to take effect.
For details on how to apply this update, which includes the changes described in this advisory, refer to:

https://access.redhat.com/articles/11258

The system must be rebooted for this update to take effect.
For details on how to apply this update, which includes the changes described in this advisory, refer to:

https://access.redhat.com/articles/11258

The system must be rebooted for this update to take effect.
For details on how to apply this update, which includes the changes described in this advisory, refer to:

https://access.redhat.com/articles/11258

The system must be rebooted for this update to take effect.
For details on how to apply this update, which includes the changes described in this advisory, refer to:

https://access.redhat.com/articles/11258

The system must be rebooted for this update to take effect.
To mitigate this issue, prevent module tipc from being loaded. Please see https://access.redhat.com/solutions/41278 for how to blacklist a kernel module to prevent it from loading automatically.