---
id: CVE-2025-68227
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  mptcp: Fix proto fallback detection with BPF

  The sockmap feature allows bpf syscall from userspace, or based
  on bpf sockops, replacing the sk_prot of sockets during pr…
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  mptcp: Fix proto fallback detection with BPF

  The sockmap feature allows bpf syscall from userspace, or based
  on bpf sockops, replacing the sk_prot of sockets during pr…
severity: none
published: '2025-12-16'
updated: '2026-10-14'
sourceUpdated: '2026-10-14T13:10:00.187'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2025-68227'
references:
  - url: 'https://git.kernel.org/stable/c/037cc50589643342d69185b663ecf9d26cce91e8'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/1a0d5c74af9b6ba9ffdf1172de5a1a6df5922a00'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/344974ea1a3ca30e4920687b0091bda4438cebdb'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/7ee8f015eb47907745e2070184a8ab1e442ac3c4'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/92c4092fe012ecdfa5fb05d394f1c1d8f91ad81c'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/9b1980b6f23fa30bf12add19f37c7458625099eb'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/c77b3b79a92e3345aa1ee296180d1af4e7031f8f'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
epss: 0.00216
epssPercentile: 0.11146
ingestedAt: '2026-10-14T13:30:58.460Z'
---

## Overview

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

mptcp: Fix proto fallback detection with BPF

The sockmap feature allows bpf syscall from userspace, or based
on bpf sockops, replacing the sk_prot of sockets during protocol stack
processing with sockmap's custom read/write interfaces.
'''
tcp_rcv_state_process()
  syn_recv_sock()/subflow_syn_recv_sock()
    tcp_init_transfer(BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB)
      bpf_skops_established       <== sockops
        bpf_sock_map_update(sk)   <== call bpf helper
          tcp_bpf_update_proto()  <== update sk_prot
'''

When the server has MPTCP enabled but the client sends a TCP SYN
without MPTCP, subflow_syn_recv_sock() performs a fallback on the
subflow, replacing the subflow sk's sk_prot with the native sk_prot.
'''
subflow_syn_recv_sock()
  subflow_ulp_fallback()
    subflow_drop_ctx()
      mptcp_subflow_ops_undo_override()
'''

Then, this subflow can be normally used by sockmap, which replaces the
native sk_prot with sockmap's custom sk_prot. The issue occurs when the
user executes accept::mptcp_stream_accept::mptcp_fallback_tcp_ops().
Here, it uses sk->sk_prot to compare with the native sk_prot, but this
is incorrect when sockmap is used, as we may incorrectly set
sk->sk_socket->ops.

This fix uses the more generic sk_family for the comparison instead.

Additionally, this also prevents a WARNING from occurring:

result from ./scripts/decode_stacktrace.sh:
------------[ cut here ]------------
WARNING: CPU: 0 PID: 337 at net/mptcp/protocol.c:68 mptcp_stream_accept \
(net/mptcp/protocol.c:4005)
Modules linked in:
...

PKRU: 55555554
Call Trace:
<TASK>
do_accept (net/socket.c:1989)
__sys_accept4 (net/socket.c:2028 net/socket.c:2057)
__x64_sys_accept (net/socket.c:2067)
x64_sys_call (arch/x86/entry/syscall_64.c:41)
do_syscall_64 (arch/x86/entry/syscall_64.c:63 arch/x86/entry/syscall_64.c:94)
entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130)
RIP: 0033:0x7f87ac92b83d

---[ end trace 0000000000000000 ]---

## Remediation

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