CVE-2025-38473: Bluetooth: Fix null-ptr-deref in l2cap_sock_resume_cb()

CVE-2025-38473: Bluetooth: Fix null-ptr-deref in l2cap_sock_resume_cb()

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

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

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

Bluetooth: Fix null-ptr-deref in l2cap_sock_resume_cb()

syzbot reported null-ptr-deref in l2cap_sock_resume_cb(). [0]

l2cap_sock_resume_cb() has a similar problem that was fixed by commit
1bff51ea59a9 ("Bluetooth: fix use-after-free error in lock_sock_nested()").

Since both l2cap_sock_kill() and l2cap_sock_resume_cb() are executed
under l2cap_sock_resume_cb(), we can avoid the issue simply by checking
if chan->data is NULL.

Let's not access to the killed socket in l2cap_sock_resume_cb().

[0]:
BUG: KASAN: null-ptr-deref in instrument_atomic_write include/linux/instrumented.h:82 [inline]
BUG: KASAN: null-ptr-deref in clear_bit include/asm-generic/bitops/instrumented-atomic.h:41 [inline]
BUG: KASAN: null-ptr-deref in l2cap_sock_resume_cb+0xb4/0x17c net/bluetooth/l2cap_sock.c:1711
Write of size 8 at addr 0000000000000570 by task kworker/u9:0/52

CPU: 1 UID: 0 PID: 52 Comm: kworker/u9:0 Not tainted 6.16.0-rc4-syzkaller-g7482bb149b9f #0 PREEMPT
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Workqueue: hci0 hci_rx_work
Call trace:
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:501 (C)
 __dump_stack+0x30/0x40 lib/dump_stack.c:94
 dump_stack_lvl+0xd8/0x12c lib/dump_stack.c:120
 print_report+0x58/0x84 mm/kasan/report.c:524
 kasan_report+0xb0/0x110 mm/kasan/report.c:634
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x264/0x2a4 mm/kasan/generic.c:189
 __kasan_check_write+0x20/0x30 mm/kasan/shadow.c:37
 instrument_atomic_write include/linux/instrumented.h:82 [inline]
 clear_bit include/asm-generic/bitops/instrumented-atomic.h:41 [inline]
 l2cap_sock_resume_cb+0xb4/0x17c net/bluetooth/l2cap_sock.c:1711
 l2cap_security_cfm+0x524/0xea0 net/bluetooth/l2cap_core.c:7357
 hci_auth_cfm include/net/bluetooth/hci_core.h:2092 [inline]
 hci_auth_complete_evt+0x2e8/0xa4c net/bluetooth/hci_event.c:3514
 hci_event_func net/bluetooth/hci_event.c:7511 [inline]
 hci_event_packet+0x650/0xe9c net/bluetooth/hci_event.c:7565
 hci_rx_work+0x320/0xb18 net/bluetooth/hci_core.c:4070
 process_one_work+0x7e8/0x155c kernel/workqueue.c:3238
 process_scheduled_works kernel/workqueue.c:3321 [inline]
 worker_thread+0x958/0xed8 kernel/workqueue.c:3402
 kthread+0x5fc/0x75c kernel/kthread.c:464
 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:847

The Linux kernel CVE team has assigned CVE-2025-38473 to this issue.


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

	Issue introduced in 3.13 with commit d97c899bde330cd1c76c3a162558177563a74362 and fixed in 6.1.147 with commit ac3a8147bb24314fb3e84986590148e79f9872ec
	Issue introduced in 3.13 with commit d97c899bde330cd1c76c3a162558177563a74362 and fixed in 6.6.100 with commit c4f16f6b071a74ac7eefe5c28985285cbbe2cd96
	Issue introduced in 3.13 with commit d97c899bde330cd1c76c3a162558177563a74362 and fixed in 6.12.40 with commit b97be7ee8a1cd96b89817cbd64a9f5cc16c17d08
	Issue introduced in 3.13 with commit d97c899bde330cd1c76c3a162558177563a74362 and fixed in 6.15.8 with commit 6d63901dcd592a1e3f71d7c6d78f9be5e8d7eef0
	Issue introduced in 3.13 with commit d97c899bde330cd1c76c3a162558177563a74362 and fixed in 6.16 with commit a0075accbf0d76c2dad1ad3993d2e944505d99a0

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-2025-38473
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:
	net/bluetooth/l2cap_sock.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/ac3a8147bb24314fb3e84986590148e79f9872ec
	https://git.kernel.org/stable/c/c4f16f6b071a74ac7eefe5c28985285cbbe2cd96
	https://git.kernel.org/stable/c/b97be7ee8a1cd96b89817cbd64a9f5cc16c17d08
	https://git.kernel.org/stable/c/6d63901dcd592a1e3f71d7c6d78f9be5e8d7eef0
	https://git.kernel.org/stable/c/a0075accbf0d76c2dad1ad3993d2e944505d99a0