Hi Luiz,
pe, 2023-08-11 kello 16:16 -0700, Luiz Augusto von Dentz kirjoitti:
> From: Luiz Augusto von Dentz <luiz.von.dentz@xxxxxxxxx>
>
> Use-after-free can occur in hci_disconnect_all_sync if a connection is
> deleted by concurrent processing of a controller event.
>
> To prevent this the code now tries to iterate over the list backwards
> to ensure the links are cleanup before its parents, also it no longer
> relies on a cursor, instead it always uses the last element since
> hci_abort_conn_sync is guaranteed to call hci_conn_del.
>
> UAF crash log:
> ==================================================================
> BUG: KASAN: slab-use-after-free in hci_set_powered_sync
> (net/bluetooth/hci_sync.c:5424) [bluetooth]
> Read of size 8 at addr ffff888009d9c000 by task kworker/u9:0/124
>
> CPU: 0 PID: 124 Comm: kworker/u9:0 Tainted: G W
> 6.5.0-rc1+ #10
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS
> 1.16.2-1.fc38 04/01/2014
> Workqueue: hci0 hci_cmd_sync_work [bluetooth]
> Call Trace:
> <TASK>
> dump_stack_lvl+0x5b/0x90
> print_report+0xcf/0x670
> ? __virt_addr_valid+0xdd/0x160
> ? hci_set_powered_sync+0x2c9/0x4a0 [bluetooth]
> kasan_report+0xa6/0xe0
> ? hci_set_powered_sync+0x2c9/0x4a0 [bluetooth]
> ? __pfx_set_powered_sync+0x10/0x10 [bluetooth]
> hci_set_powered_sync+0x2c9/0x4a0 [bluetooth]
> ? __pfx_hci_set_powered_sync+0x10/0x10 [bluetooth]
> ? __pfx_lock_release+0x10/0x10
> ? __pfx_set_powered_sync+0x10/0x10 [bluetooth]
> hci_cmd_sync_work+0x137/0x220 [bluetooth]
> process_one_work+0x526/0x9d0
> ? __pfx_process_one_work+0x10/0x10
> ? __pfx_do_raw_spin_lock+0x10/0x10
> ? mark_held_locks+0x1a/0x90
> worker_thread+0x92/0x630
> ? __pfx_worker_thread+0x10/0x10
> kthread+0x196/0x1e0
> ? __pfx_kthread+0x10/0x10
> ret_from_fork+0x2c/0x50
> </TASK>
>
> Allocated by task 1782:
> kasan_save_stack+0x33/0x60
> kasan_set_track+0x25/0x30
> __kasan_kmalloc+0x8f/0xa0
> hci_conn_add+0xa5/0xa80 [bluetooth]
> hci_bind_cis+0x881/0x9b0 [bluetooth]
> iso_connect_cis+0x121/0x520 [bluetooth]
> iso_sock_connect+0x3f6/0x790 [bluetooth]
> __sys_connect+0x109/0x130
> __x64_sys_connect+0x40/0x50
> do_syscall_64+0x60/0x90
> entry_SYSCALL_64_after_hwframe+0x6e/0xd8
>
> Freed by task 695:
> kasan_save_stack+0x33/0x60
> kasan_set_track+0x25/0x30
> kasan_save_free_info+0x2b/0x50
> __kasan_slab_free+0x10a/0x180
> __kmem_cache_free+0x14d/0x2e0
> device_release+0x5d/0xf0
> kobject_put+0xdf/0x270
> hci_disconn_complete_evt+0x274/0x3a0 [bluetooth]
> hci_event_packet+0x579/0x7e0 [bluetooth]
> hci_rx_work+0x287/0xaa0 [bluetooth]
> process_one_work+0x526/0x9d0
> worker_thread+0x92/0x630
> kthread+0x196/0x1e0
> ret_from_fork+0x2c/0x50
> ==================================================================
>
> Fixes: 182ee45da083 ("Bluetooth: hci_sync: Rework hci_suspend_notifier")
> Signed-off-by: Pauli Virtanen <pav@xxxxxx>
> Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@xxxxxxxxx>
> ---
> net/bluetooth/hci_sync.c | 51 ++++++++++++++++++++++++----------------
> 1 file changed, 31 insertions(+), 20 deletions(-)
>
> diff --git a/net/bluetooth/hci_sync.c b/net/bluetooth/hci_sync.c
> index 5eb30ba21370..86e18e09136e 100644
> --- a/net/bluetooth/hci_sync.c
> +++ b/net/bluetooth/hci_sync.c
> @@ -5370,6 +5370,7 @@ int hci_abort_conn_sync(struct hci_dev *hdev, struct hci_conn *conn, u8 reason)
> {
> int err = 0;
> u16 handle = conn->handle;
> + struct hci_conn *c;
>
> switch (conn->state) {
> case BT_CONNECTED:
> @@ -5389,43 +5390,53 @@ int hci_abort_conn_sync(struct hci_dev *hdev, struct hci_conn *conn, u8 reason)
> hci_dev_unlock(hdev);
> return 0;
> default:
> + hci_dev_lock(hdev);
> conn->state = BT_CLOSED;
> + hci_disconn_cfm(conn, reason);
> + hci_conn_del(conn);
> + hci_dev_unlock(hdev);
> return 0;
> }
>
> + /* Check if the connection hasn't been cleanup while waiting
> + * commands to complete.
> + */
> + c = hci_conn_hash_lookup_handle(hdev, handle);
> + if (!c || c != conn)
> + return 0;
> +
> /* Cleanup hci_conn object if it cannot be cancelled as it
> * likelly means the controller and host stack are out of sync
> * or in case of LE it was still scanning so it can be cleanup
> * safely.
> */
> - if (err) {
> - struct hci_conn *c;
> -
> - /* Check if the connection hasn't been cleanup while waiting
> - * commands to complete.
> - */
> - c = hci_conn_hash_lookup_handle(hdev, handle);
> - if (!c || c != conn)
> - return 0;
> -
> - hci_dev_lock(hdev);
> - hci_conn_failed(conn, err);
> - hci_dev_unlock(hdev);
> - }
> + hci_dev_lock(hdev);
> + hci_conn_failed(conn, reason);
> + hci_dev_unlock(hdev);
To me it seems there is a theoretical race here:
task 1 in hci_conn_abort_sync
task 2 in hci_disconn_complete_evt
task 1: c = hci_conn_hash_lookup_handle(conn->handle)
task 2: hci_dev_lock(hdev)
task 1: hci_dev_lock(hdev) /* waits here */
task 2: hci_conn_del(conn) /* conn deleted the first time */
task 2: hci_dev_unlock(hdev)
task 1: hci_conn_failed(conn, err) /* conn deleted again */
Moving hci_dev_lock before hci_conn_hash_lookup_handle avoids this.
Another related theoretical race seems to be in e.g.
hci_acl/sco/isodata_packet which do
hci_dev_lock(hdev);
conn = hci_conn_hash_lookup_handle(hdev, handle);
hci_dev_unlock(hdev);
if (conn)
do_stuff_without_lock(conn);
These tasks run in hdev->workqueue, so it seems like deletion of conn
in hdev->req_workqueue like in hci_conn_abort_sync here could in theory
occur while do_stuff_without_lock is still accessing conn.
I guess in reality it depends on whether the two workqueues are really
running the tasks on different CPU at the same time, and if one can hit
narrow time windows.
>
> return err;
> }
>
> static int hci_disconnect_all_sync(struct hci_dev *hdev, u8 reason)
> {
> - struct hci_conn *conn, *tmp;
> - int err;
> + struct list_head *head = &hdev->conn_hash.list;
> + struct hci_conn *conn;
>
> - list_for_each_entry_safe(conn, tmp, &hdev->conn_hash.list, list) {
> - err = hci_abort_conn_sync(hdev, conn, reason);
> - if (err)
> - return err;
> + rcu_read_lock();
> + while ((conn = list_first_or_null_rcu(head, struct hci_conn, list))) {
> + /* Make sure the connection is not freed while unlocking */
> + conn = hci_conn_get(conn);
> + rcu_read_unlock();
> + /* Disregard possible errors since hci_conn_del shall have been
> + * called even in case of errors had occurred since it would
> + * then cause hci_conn_failed to be called which calls
> + * hci_conn_del internally.
> + */
> + hci_abort_conn_sync(hdev, conn, reason);
> + hci_conn_put(conn);
> + rcu_read_lock();
> }
> + rcu_read_unlock();
>
> return 0;
> }
