---
id: CVE-2026-80819
title: 'Bluetooth: RFCOMM: take rfcomm_mutex for the deferred setup accept'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  Bluetooth: RFCOMM: take rfcomm_mutex for the deferred setup accept

  rfcomm_sock_recvmsg() completes a deferred setup by calling
  rfcomm_dlc_accept() without holding any …
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= bb23c0ab824653be4aa7dfca15b07b3059717004 <
    d8d686dd5662a7c4745e4515f1237a9f3b7df181
  - >-
    Linux >= bb23c0ab824653be4aa7dfca15b07b3059717004 <
    eb71d5a1ea8ff2683e394b48ae3cd676037ab4c2
  - >-
    Linux >= bb23c0ab824653be4aa7dfca15b07b3059717004 <
    56f0aa75c7640e46397ef73bea251fcbef9150c0
  - >-
    Linux >= bb23c0ab824653be4aa7dfca15b07b3059717004 <
    362726c9c6e56eea4262109183e49868c39ccd3a
  - >-
    Linux >= bb23c0ab824653be4aa7dfca15b07b3059717004 <
    825b95561d7b7c393df9e7bc295451aaeadc3d18
  - >-
    Linux >= bb23c0ab824653be4aa7dfca15b07b3059717004 <
    d4b1a13b1eff2e80925c7368ffdeaaa50cba93df
  - >-
    Linux >= bb23c0ab824653be4aa7dfca15b07b3059717004 <
    355bfd57ca4ca881c6eb03ca813b440a094b1f44
  - >-
    Linux >= bb23c0ab824653be4aa7dfca15b07b3059717004 <
    b405c2f96ae2e37375105881890f7738833b1d62
  - >-
    Linux >= bb23c0ab824653be4aa7dfca15b07b3059717004 <
    43a556b2fd43f2df6dded59c2e26560a27874c24
  - Linux 2.6.30
published: '2026-09-04'
updated: '2026-10-19'
sourceUpdated: '2026-10-19T08:44:12.945Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-80819'
references:
  - url: 'https://git.kernel.org/stable/c/d8d686dd5662a7c4745e4515f1237a9f3b7df181'
  - url: 'https://git.kernel.org/stable/c/eb71d5a1ea8ff2683e394b48ae3cd676037ab4c2'
  - url: 'https://git.kernel.org/stable/c/56f0aa75c7640e46397ef73bea251fcbef9150c0'
  - url: 'https://git.kernel.org/stable/c/362726c9c6e56eea4262109183e49868c39ccd3a'
  - url: 'https://git.kernel.org/stable/c/825b95561d7b7c393df9e7bc295451aaeadc3d18'
  - url: 'https://git.kernel.org/stable/c/d4b1a13b1eff2e80925c7368ffdeaaa50cba93df'
  - url: 'https://git.kernel.org/stable/c/355bfd57ca4ca881c6eb03ca813b440a094b1f44'
  - url: 'https://git.kernel.org/stable/c/b405c2f96ae2e37375105881890f7738833b1d62'
  - url: 'https://git.kernel.org/stable/c/43a556b2fd43f2df6dded59c2e26560a27874c24'
tags:
  - cve.org
epss: 0.00195
epssPercentile: 0.08586
ingestedAt: '2026-10-19T09:16:01.505Z'
---

## Overview

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

Bluetooth: RFCOMM: take rfcomm_mutex for the deferred setup accept

rfcomm_sock_recvmsg() completes a deferred setup by calling
rfcomm_dlc_accept() without holding any RFCOMM lock:

	if (test_and_clear_bit(RFCOMM_DEFER_SETUP, &d->flags)) {
		rfcomm_dlc_accept(d);
		return 0;
	}

and rfcomm_dlc_accept() dereferences the session on its first line:

	struct sock *sk = d->session->sock->sk;

Every other path that touches d->session runs under rfcomm_mutex:
rfcomm_dlc_open(), rfcomm_dlc_close(), rfcomm_dlc_exists(),
rfcomm_dlc_send_rpn(), and the RFCOMM thread through
rfcomm_process_sessions(). rfcomm_connect_ind() is even documented as
"called under rfcomm_lock()". This call site is the only one that skips
it.

The RFCOMM_DEFER_SETUP bit looks like it serialises the accept against
teardown, since __rfcomm_dlc_close() returns early when it wins the
test_and_clear. But rfcomm_recv_disc() forces the state first:

	d->state = BT_CLOSED;
	__rfcomm_dlc_close(d, err);

and the early return only covers BT_CONNECT, BT_CONFIG, BT_OPEN and
BT_CONNECT2. With the state already BT_CLOSED that switch does not
match, the bit is never consulted, and __rfcomm_dlc_close() falls
through to rfcomm_dlc_unlink(), which sets d->session = NULL.

So a remote DISC on a deferred dlc clears the session while leaving
RFCOMM_DEFER_SETUP set. The next recvmsg() then passes the
test_and_clear and dereferences a NULL session. No timing window is
needed: once the DISC has been processed, the dereference is
unconditional.

Give rfcomm_dlc_accept() the same shape as rfcomm_dlc_open() and
rfcomm_dlc_close(): an exported wrapper that takes rfcomm_mutex and
re-checks the session, around a __rfcomm_dlc_accept() that the two
in-core callers, which already hold the mutex, keep using.

Reproduced on a KASAN + PROVE_LOCKING kernel with a BR/EDR peer emulated
over /dev/vhci: the peer brings up an ACL link, opens L2CAP on the
RFCOMM PSM, starts a session, opens a dlc on a channel bound with
BT_DEFER_SETUP, and sends DISC after the socket is accepted. recv() on
the accepted socket then hits:

  Oops: general protection fault
  KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017]
  RIP: 0010:rfcomm_dlc_accept+0x54/0x350
  Call Trace:
    rfcomm_sock_recvmsg+0x1cd/0x230
    sock_recvmsg+0x166/0x1c0
    __sys_recvfrom+0x20d/0x300

0x10 is the offset of sock in struct rfcomm_session. With this patch the
same run completes with recv() returning 0 and no report, and lockdep
stays quiet, confirming rfcomm_mutex is still taken before lock_sock on
this path as it is on the thread side.

## Affected

- `Linux >= bb23c0ab824653be4aa7dfca15b07b3059717004 < d8d686dd5662a7c4745e4515f1237a9f3b7df181`
- `Linux >= bb23c0ab824653be4aa7dfca15b07b3059717004 < eb71d5a1ea8ff2683e394b48ae3cd676037ab4c2`
- `Linux >= bb23c0ab824653be4aa7dfca15b07b3059717004 < 56f0aa75c7640e46397ef73bea251fcbef9150c0`
- `Linux >= bb23c0ab824653be4aa7dfca15b07b3059717004 < 362726c9c6e56eea4262109183e49868c39ccd3a`
- `Linux >= bb23c0ab824653be4aa7dfca15b07b3059717004 < 825b95561d7b7c393df9e7bc295451aaeadc3d18`
- `Linux >= bb23c0ab824653be4aa7dfca15b07b3059717004 < d4b1a13b1eff2e80925c7368ffdeaaa50cba93df`
- `Linux >= bb23c0ab824653be4aa7dfca15b07b3059717004 < 355bfd57ca4ca881c6eb03ca813b440a094b1f44`
- `Linux >= bb23c0ab824653be4aa7dfca15b07b3059717004 < b405c2f96ae2e37375105881890f7738833b1d62`
- `Linux >= bb23c0ab824653be4aa7dfca15b07b3059717004 < 43a556b2fd43f2df6dded59c2e26560a27874c24`
- `Linux 2.6.30`

## Remediation

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