Bluetooth: L2CAP: Fix use-after-free caused by l2cap_reassemble_sdu
CVE: CVE-2022-49910
Component: kernel
CWE: CWE-416
Severity: Important
CVSS v3: 7.2/AV:A/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
Release date: 2022-01-01T00:00:00+00:00

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

Bluetooth: L2CAP: Fix use-after-free caused by l2cap_reassemble_sdu

Fix the race condition between the following two flows that run in
parallel:

1. l2cap_reassemble_sdu -> chan->ops->recv (l2cap_sock_recv_cb) ->
   __sock_queue_rcv_skb.

2. bt_sock_recvmsg -> skb_recv_datagram, skb_free_datagram.

An SKB can be queued by the first flow and immediately dequeued and
freed by the second flow, therefore the callers of l2cap_reassemble_sdu
can't use the SKB after that function returns. However, some places
continue accessing struct l2cap_ctrl that resides in the SKB's CB for a
short time after l2cap_reassemble_sdu returns, leading to a
use-after-free condition (the stack trace is below, line numbers for
kernel 5.19.8).

Fix it by keeping a local copy of struct l2cap_ctrl.

BUG: KASAN: use-after-free in l2cap_rx_state_recv (net/bluetooth/l2cap_core.c:6906) bluetooth
Read of size 1 at addr ffff88812025f2f0 by task kworker/u17:3/43169

Workqueue: hci0 hci_rx_work [bluetooth]
Call Trace:
 <TASK>
 dump_stack_lvl (lib/dump_stack.c:107 (discriminator 4))
 print_report.cold (mm/kasan/report.c:314 mm/kasan/report.c:429)
 ? l2cap_rx_state_recv (net/bluetooth/l2cap_core.c:6906) bluetooth
 kasan_report (mm/kasan/report.c:162 mm/kasan/report.c:493)
 ? l2cap_rx_state_recv (net/bluetooth/l2cap_core.c:6906) bluetooth
 l2cap_rx_state_recv (net/bluetooth/l2cap_core.c:6906) bluetooth
 l2cap_rx (net/bluetooth/l2cap_core.c:7236 net/bluetooth/l2cap_core.c:7271) bluetooth
 ret_from_fork (arch/x86/entry/entry_64.S:306)
 </TASK>

Allocated by task 43169:
 kasan_save_stack (mm/kasan/common.c:39)
 __kasan_slab_alloc (mm/kasan/common.c:45 mm/kasan/common.c:436 mm/kasan/common.c:469)
 kmem_cache_alloc_node (mm/slab.h:750 mm/slub.c:3243 mm/slub.c:3293)
 __alloc_skb (net/core/skbuff.c:414)
 l2cap_recv_frag (./include/net/bluetooth/bluetooth.h:425 net/bluetooth/l2cap_core.c:8329) bluetooth
 l2cap_recv_acldata (net/bluetooth/l2cap_core.c:8442) bluetooth
 hci_rx_work (net/bluetooth/hci_core.c:3642 net/bluetooth/hci_core.c:3832) bluetooth
 process_one_work (kernel/workqueue.c:2289)
 worker_thread (./include/linux/list.h:292 kernel/workqueue.c:2437)
 kthread (kernel/kthread.c:376)
 ret_from_fork (arch/x86/entry/entry_64.S:306)

Freed by task 27920:
 kasan_save_stack (mm/kasan/common.c:39)
 kasan_set_track (mm/kasan/common.c:45)
 kasan_set_free_info (mm/kasan/generic.c:372)
 ____kasan_slab_free (mm/kasan/common.c:368 mm/kasan/common.c:328)
 slab_free_freelist_hook (mm/slub.c:1780)
 kmem_cache_free (mm/slub.c:3536 mm/slub.c:3553)
 skb_free_datagram (./include/net/sock.h:1578 ./include/net/sock.h:1639 net/core/datagram.c:323)
 bt_sock_recvmsg (net/bluetooth/af_bluetooth.c:295) bluetooth
 l2cap_sock_recvmsg (net/bluetooth/l2cap_sock.c:1212) bluetooth
 sock_read_iter (net/socket.c:1087)
 new_sync_read (./include/linux/fs.h:2052 fs/read_write.c:401)
 vfs_read (fs/read_write.c:482)
 ksys_read (fs/read_write.c:620)
 do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80)
 entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:120)

Statement: The bug could happen if Bluetooth being used. Due to the complexity to reproduce it where kind of race condition should happen between bt_sock_recvmsg and l2cap_reassemble_sdu functions. The bug already fixed for the Red Hat Enterprise Linux 9 (all versions) and later, and actual only for Red Hat Enterprise Linux 8.

Remediation:
The only way to mitigate these vulnerabilities on the operating system level is to disable the Bluetooth functionality via blacklisting kernel modules in the Linux kernel. The kernel modules can be prevented from being loaded by using system-wide modprobe rules. How to disable Bluetooth modules instructions are available on the Customer Portal at https://access.redhat.com/solutions/2682931.

Alternatively, Bluetooth can be disabled within the hardware or at BIOS level, which will also provide an effective mitigation as the kernel will not be able to detect that Bluetooth hardware is present on the system.