---
id: CVE-2023-53781
title: 'smc: Fix use-after-free in tcp_write_timer_handler().'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  smc: Fix use-after-free in tcp_write_timer_handler().

  With Eric's ref tracker, syzbot finally found a repro for
  use-after-free in tcp_write_timer_handler() by kernel T…
severity: high
cvss: 7.8
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'
cvssSource: cna
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= ac7138746e14137a451f8539614cdd349153e0c0 <
    1cc41c8acfc1ee30b4868559058db97fa44b0137
  - >-
    Linux >= ac7138746e14137a451f8539614cdd349153e0c0 <
    9744d2bf19762703704ecba885b7ac282c02eacf
  - Linux 4.11
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: total
  timestamp: '2026-10-15T21:37:08.667404Z'
published: '2025-12-09'
updated: '2026-10-15'
sourceUpdated: '2026-10-15T21:41:35.733Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2023-53781'
references:
  - url: 'https://git.kernel.org/stable/c/1cc41c8acfc1ee30b4868559058db97fa44b0137'
  - url: 'https://git.kernel.org/stable/c/9744d2bf19762703704ecba885b7ac282c02eacf'
tags:
  - cve.org
epss: 0.00144
epssPercentile: 0.03294
ingestedAt: '2026-10-15T22:48:25.419Z'
---

## Overview

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

smc: Fix use-after-free in tcp_write_timer_handler().

With Eric's ref tracker, syzbot finally found a repro for
use-after-free in tcp_write_timer_handler() by kernel TCP
sockets. [0]

If SMC creates a kernel socket in __smc_create(), the kernel
socket is supposed to be freed in smc_clcsock_release() by
calling sock_release() when we close() the parent SMC socket.

However, at the end of smc_clcsock_release(), the kernel
socket's sk_state might not be TCP_CLOSE.  This means that
we have not called inet_csk_destroy_sock() in __tcp_close()
and have not stopped the TCP timers.

The kernel socket's TCP timers can be fired later, so we
need to hold a refcnt for net as we do for MPTCP subflows
in mptcp_subflow_create_socket().

[0]:
leaked reference.
 sk_alloc (./include/net/net_namespace.h:335 net/core/sock.c:2108)
 inet_create (net/ipv4/af_inet.c:319 net/ipv4/af_inet.c:244)
 __sock_create (net/socket.c:1546)
 smc_create (net/smc/af_smc.c:3269 net/smc/af_smc.c:3284)
 __sock_create (net/socket.c:1546)
 __sys_socket (net/socket.c:1634 net/socket.c:1618 net/socket.c:1661)
 __x64_sys_socket (net/socket.c:1672)
 do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80)
 entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:120)
==================================================================
BUG: KASAN: slab-use-after-free in tcp_write_timer_handler (net/ipv4/tcp_timer.c:378 net/ipv4/tcp_timer.c:624 net/ipv4/tcp_timer.c:594)
Read of size 1 at addr ffff888052b65e0d by task syzrepro/18091

CPU: 0 PID: 18091 Comm: syzrepro Tainted: G        W          6.3.0-rc4-01174-gb5d54eb5899a #7
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.0-1.amzn2022.0.1 04/01/2014
Call Trace:
 <IRQ>
 dump_stack_lvl (lib/dump_stack.c:107)
 print_report (mm/kasan/report.c:320 mm/kasan/report.c:430)
 kasan_report (mm/kasan/report.c:538)
 tcp_write_timer_handler (net/ipv4/tcp_timer.c:378 net/ipv4/tcp_timer.c:624 net/ipv4/tcp_timer.c:594)
 tcp_write_timer (./include/linux/spinlock.h:390 net/ipv4/tcp_timer.c:643)
 call_timer_fn (./arch/x86/include/asm/jump_label.h:27 ./include/linux/jump_label.h:207 ./include/trace/events/timer.h:127 kernel/time/timer.c:1701)
 __run_timers.part.0 (kernel/time/timer.c:1752 kernel/time/timer.c:2022)
 run_timer_softirq (kernel/time/timer.c:2037)
 __do_softirq (./arch/x86/include/asm/jump_label.h:27 ./include/linux/jump_label.h:207 ./include/trace/events/irq.h:142 kernel/softirq.c:572)
 __irq_exit_rcu (kernel/softirq.c:445 kernel/softirq.c:650)
 irq_exit_rcu (kernel/softirq.c:664)
 sysvec_apic_timer_interrupt (arch/x86/kernel/apic/apic.c:1107 (discriminator 14))
 </IRQ>

## Affected

- `Linux >= ac7138746e14137a451f8539614cdd349153e0c0 < 1cc41c8acfc1ee30b4868559058db97fa44b0137`
- `Linux >= ac7138746e14137a451f8539614cdd349153e0c0 < 9744d2bf19762703704ecba885b7ac282c02eacf`
- `Linux 4.11`

## Remediation

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