---
id: CVE-2026-63979
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  net/handshake: hand off the pinned file reference to accept_doit

  handshake_req_next() removes the request from the per-net
  pending list and drops hn_lock before handsh…
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  net/handshake: hand off the pinned file reference to accept_doit

  handshake_req_next() removes the request from the per-net
  pending list and drops hn_lock before handsh…
severity: critical
cvss: 9.8
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'
published: '2026-07-19'
updated: '2026-08-09'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-63979'
references:
  - url: 'https://git.kernel.org/stable/c/68eba6519cbd6359fb554a9720f3a3b6b2eba23f'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/c06876d4fac38f35820946ee3b1be7d7da799cd4'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/f4251190e58b209999c1ba9e6d2976136a1be055'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
epss: 0.00649
epssPercentile: 0.48953
ingestedAt: '2026-08-09T19:34:41.175Z'
---

## Overview

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

net/handshake: hand off the pinned file reference to accept_doit

handshake_req_next() removes the request from the per-net
pending list and drops hn_lock before handshake_nl_accept_doit()
reads req->hr_sk->sk_socket and dereferences sock->file (once in
FD_PREPARE() and again in get_file()).  In that window a
consumer running tls_handshake_cancel() followed by sockfd_put()
(svc_sock_free) or __fput_sync() (xs_reset_transport) releases
sock->file.  sock_release() then runs sock_orphan(), zeroing
sk_socket, and frees the struct socket.  The accept-side code
either reads NULL through sk_socket or chases freed memory.

The submit-side sock_hold() does not prevent this.  sk_refcnt
protects struct sock, but struct socket and sock->file are
independently refcounted via the file descriptor the consumer
owns.  Pinning sk leaves sock and sock->file unprotected.

Retarget the accept-side dereferences at req->hr_file, which was
pinned at submit time, instead of req->hr_sk->sk_socket->file.
Pinning on its own is not sufficient: a consumer that cancels
between handshake_req_next() returning and accept_doit reaching
FD_PREPARE() takes the !remove_pending() branch in
handshake_req_cancel() and drops hr_file before the accept side
takes its own reference.  Hand off an additional file reference
inside handshake_req_next(), under hn_lock, so the accept side
operates on a reference that no concurrent handshake_req_cancel()
can revoke.  FD_PREPARE() consumes that handed-off reference,
either by transferring it to the new fd in fd_publish() or by
dropping it in the cleanup destructor on error; the explicit
get_file() that previously balanced FD_PREPARE() is therefore
redundant and goes away.

Update handshake_req_cancel_test2 and _test3 to simulate the
FD_PREPARE() consumption with an fput() so the kunit file-count
assertions stay balanced.

## Remediation

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