Hi,
On Tue, Jul 13, 2021 at 8:20 PM Wang ShaoBo <bobo.shaobowang@xxxxxxxxxx> wrote:
>
> use-after-free error in lock_sock_nested() is reported:
>
> [ 179.140137][ T3731] =====================================================
> [ 179.142675][ T3731] BUG: KMSAN: use-after-free in lock_sock_nested+0x280/0x2c0
> [ 179.145494][ T3731] CPU: 4 PID: 3731 Comm: kworker/4:2 Not tainted 5.12.0-rc6+ #54
> [ 179.148432][ T3731] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014
> [ 179.151806][ T3731] Workqueue: events l2cap_chan_timeout
> [ 179.152730][ T3731] Call Trace:
> [ 179.153301][ T3731] dump_stack+0x24c/0x2e0
> [ 179.154063][ T3731] kmsan_report+0xfb/0x1e0
> [ 179.154855][ T3731] __msan_warning+0x5c/0xa0
> [ 179.155579][ T3731] lock_sock_nested+0x280/0x2c0
> [ 179.156436][ T3731] ? kmsan_get_metadata+0x116/0x180
> [ 179.157257][ T3731] l2cap_sock_teardown_cb+0xb8/0x890
> [ 179.158154][ T3731] ? __msan_metadata_ptr_for_load_8+0x10/0x20
> [ 179.159141][ T3731] ? kmsan_get_metadata+0x116/0x180
> [ 179.159994][ T3731] ? kmsan_get_shadow_origin_ptr+0x84/0xb0
> [ 179.160959][ T3731] ? l2cap_sock_recv_cb+0x420/0x420
> [ 179.161834][ T3731] l2cap_chan_del+0x3e1/0x1d50
> [ 179.162608][ T3731] ? kmsan_get_metadata+0x116/0x180
> [ 179.163435][ T3731] ? kmsan_get_shadow_origin_ptr+0x84/0xb0
> [ 179.164406][ T3731] l2cap_chan_close+0xeea/0x1050
> [ 179.165189][ T3731] ? kmsan_internal_unpoison_shadow+0x42/0x70
> [ 179.166180][ T3731] l2cap_chan_timeout+0x1da/0x590
> [ 179.167066][ T3731] ? __msan_metadata_ptr_for_load_8+0x10/0x20
> [ 179.168023][ T3731] ? l2cap_chan_create+0x560/0x560
> [ 179.168818][ T3731] process_one_work+0x121d/0x1ff0
> [ 179.169598][ T3731] worker_thread+0x121b/0x2370
> [ 179.170346][ T3731] kthread+0x4ef/0x610
> [ 179.171010][ T3731] ? process_one_work+0x1ff0/0x1ff0
> [ 179.171828][ T3731] ? kthread_blkcg+0x110/0x110
> [ 179.172587][ T3731] ret_from_fork+0x1f/0x30
> [ 179.173348][ T3731]
> [ 179.173752][ T3731] Uninit was created at:
> [ 179.174409][ T3731] kmsan_internal_poison_shadow+0x5c/0xf0
> [ 179.175373][ T3731] kmsan_slab_free+0x76/0xc0
> [ 179.176060][ T3731] kfree+0x3a5/0x1180
> [ 179.176664][ T3731] __sk_destruct+0x8af/0xb80
> [ 179.177375][ T3731] __sk_free+0x812/0x8c0
> [ 179.178032][ T3731] sk_free+0x97/0x130
> [ 179.178686][ T3731] l2cap_sock_release+0x3d5/0x4d0
> [ 179.179457][ T3731] sock_close+0x150/0x450
> [ 179.180117][ T3731] __fput+0x6bd/0xf00
> [ 179.180787][ T3731] ____fput+0x37/0x40
> [ 179.181481][ T3731] task_work_run+0x140/0x280
> [ 179.182219][ T3731] do_exit+0xe51/0x3e60
> [ 179.182930][ T3731] do_group_exit+0x20e/0x450
> [ 179.183656][ T3731] get_signal+0x2dfb/0x38f0
> [ 179.184344][ T3731] arch_do_signal_or_restart+0xaa/0xe10
> [ 179.185266][ T3731] exit_to_user_mode_prepare+0x2d2/0x560
> [ 179.186136][ T3731] syscall_exit_to_user_mode+0x35/0x60
> [ 179.186984][ T3731] do_syscall_64+0xc5/0x140
> [ 179.187681][ T3731] entry_SYSCALL_64_after_hwframe+0x44/0xae
> [ 179.188604][ T3731] =====================================================
>
> In our case, there are two Thread A and B:
>
> Context: Thread A: Context: Thread B:
>
> l2cap_chan_timeout() __se_sys_shutdown()
> l2cap_chan_close() l2cap_sock_shutdown()
> l2cap_chan_del() l2cap_chan_close()
> l2cap_sock_teardown_cb() l2cap_sock_teardown_cb()
>
> Once l2cap_sock_teardown_cb() excuted, this sock will be marked as SOCK_ZAPPED,
> and can be treated as killable in l2cap_sock_kill() if sock_orphan() has
> excuted, at this time we close sock through sock_close() which end to call
> l2cap_sock_kill() like Thread C:
>
> Context: Thread C:
>
> sock_close()
> l2cap_sock_release()
> sock_orphan()
> l2cap_sock_kill() #free sock if refcnt is 1
>
> If C completed, Once A or B reaches l2cap_sock_teardown_cb() again,
> use-after-free happened.
>
> We should set chan->data to NULL if sock is freed, for telling teardown
> operation is not allowed in l2cap_sock_teardown_cb(), and also we should
> avoid killing an already killed socket in l2cap_sock_close_cb().
>
> Signed-off-by: Wang ShaoBo <bobo.shaobowang@xxxxxxxxxx>
> ---
> net/bluetooth/l2cap_sock.c | 14 ++++++++++++--
> 1 file changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c
> index c99d65ef13b1..ddc6a692b237 100644
> --- a/net/bluetooth/l2cap_sock.c
> +++ b/net/bluetooth/l2cap_sock.c
> @@ -1215,14 +1215,18 @@ static int l2cap_sock_recvmsg(struct socket *sock, struct msghdr *msg,
> */
> static void l2cap_sock_kill(struct sock *sk)
> {
> + struct l2cap_chan *chan;
> +
> if (!sock_flag(sk, SOCK_ZAPPED) || sk->sk_socket)
> return;
>
> BT_DBG("sk %p state %s", sk, state_to_string(sk->sk_state));
>
> /* Kill poor orphan */
> -
> - l2cap_chan_put(l2cap_pi(sk)->chan);
> + chan = l2cap_pi(sk)->chan;
> + l2cap_chan_put(chan);
> + if (refcount_read(&sk->sk_refcnt) == 1)
> + chan->data = NULL;
Instead of checking if it is the last reference here, wouldn't it be
better to reset the chan->data to NULL on l2cap_sock_destruct?
> sock_set_flag(sk, SOCK_DEAD);
> sock_put(sk);
> }
> @@ -1508,6 +1512,9 @@ static void l2cap_sock_close_cb(struct l2cap_chan *chan)
> {
> struct sock *sk = chan->data;
>
> + if (!sk)
> + return;
> +
> l2cap_sock_kill(sk);
> }
>
> @@ -1516,6 +1523,9 @@ static void l2cap_sock_teardown_cb(struct l2cap_chan *chan, int err)
> struct sock *sk = chan->data;
> struct sock *parent;
>
> + if (!sk)
> + return;
> +
> BT_DBG("chan %p state %s", chan, state_to_string(chan->state));
>
> /* This callback can be called both for server (BT_LISTEN)
> --
> 2.27.0
>
--
Luiz Augusto von Dentz
