CVE-2026-64557: Bluetooth: L2CAP: Fix use-after-free in l2cap_sock_new_connection_cb()

From: Greg Kroah-Hartman <[email protected]>

Description
===========

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

Bluetooth: L2CAP: Fix use-after-free in l2cap_sock_new_connection_cb()

l2cap_sock_new_connection_cb() returned l2cap_pi(sk)->chan after
release_sock(parent). Once the parent lock is dropped the newly
enqueued child socket sk is reachable via the accept queue, so another
task can accept and free it before the callback dereferences sk,
resulting in a use-after-free.

Rework the ->new_connection() op so the core, rather than the callback,
owns the child channel's lifetime. The op now receives a pre-allocated
new_chan and returns an errno instead of allocating and returning a
channel. l2cap_new_connection() allocates the child channel and links
it into the conn list via __l2cap_chan_add() before invoking the
callback, so the conn-list reference keeps the channel alive once
release_sock(parent) exposes the socket to other tasks.

Channel configuration that was duplicated in l2cap_sock_init() and the
various new_connection callbacks is consolidated into
l2cap_chan_set_defaults(), which now inherits from the parent channel
when one is supplied.

The Linux kernel CVE team has assigned CVE-2026-64557 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 3.13 with commit 8ffb929098a56939ac71509302eeab5b207bf262 and fixed in 6.1.178 with commit b39298044e5534612511a2ff5de03ba5f6e7a820
	Issue introduced in 3.13 with commit 8ffb929098a56939ac71509302eeab5b207bf262 and fixed in 6.6.145 with commit 8c37e4338c801ebb8cee52436c01c41e009f6e87
	Issue introduced in 3.13 with commit 8ffb929098a56939ac71509302eeab5b207bf262 and fixed in 6.12.97 with commit 84e718b6a814edc84159361f9f454a4e92ae91ae
	Issue introduced in 3.13 with commit 8ffb929098a56939ac71509302eeab5b207bf262 and fixed in 6.18.40 with commit 36da806f7fbaee56ad9e81859deec203f9728700
	Issue introduced in 3.13 with commit 8ffb929098a56939ac71509302eeab5b207bf262 and fixed in 7.1.5 with commit 733e76e74e406c1d1ddc7369420dd8a47f48bb8a
	Issue introduced in 3.13 with commit 8ffb929098a56939ac71509302eeab5b207bf262 and fixed in 7.2-rc3 with commit 6fef032af0092ed5ccb767239a9ac1bc38c08a40

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-64557
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	include/net/bluetooth/l2cap.h
	net/bluetooth/6lowpan.c
	net/bluetooth/l2cap_core.c
	net/bluetooth/l2cap_sock.c
	net/bluetooth/smp.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/b39298044e5534612511a2ff5de03ba5f6e7a820
	https://git.kernel.org/stable/c/8c37e4338c801ebb8cee52436c01c41e009f6e87
	https://git.kernel.org/stable/c/84e718b6a814edc84159361f9f454a4e92ae91ae
	https://git.kernel.org/stable/c/36da806f7fbaee56ad9e81859deec203f9728700
	https://git.kernel.org/stable/c/733e76e74e406c1d1ddc7369420dd8a47f48bb8a
	https://git.kernel.org/stable/c/6fef032af0092ed5ccb767239a9ac1bc38c08a40