On Wed, Jun 22, 2022 at 10:27 AM Lee Jones <lee.jones@xxxxxxxxxx> wrote:
>
> This change prevents a use-after-free caused by one of the worker
> threads starting up (see below) *after* the final channel reference
> has been put() during sock_close() but *before* the references to the
> channel have been destroyed.
>
> refcount_t: increment on 0; use-after-free.
> BUG: KASAN: use-after-free in refcount_dec_and_test+0x20/0xd0
> Read of size 4 at addr ffffffc114f5bf18 by task kworker/u17:14/705
>
> CPU: 4 PID: 705 Comm: kworker/u17:14 Tainted: G S W 4.14.234-00003-g1fb6d0bd49a4-dirty #28
> Hardware name: Qualcomm Technologies, Inc. SM8150 V2 PM8150 Google Inc. MSM sm8150 Flame DVT (DT)
> Workqueue: hci0 hci_rx_work
> Call trace:
> dump_backtrace+0x0/0x378
> show_stack+0x20/0x2c
> dump_stack+0x124/0x148
> print_address_description+0x80/0x2e8
> __kasan_report+0x168/0x188
> kasan_report+0x10/0x18
> __asan_load4+0x84/0x8c
> refcount_dec_and_test+0x20/0xd0
> l2cap_chan_put+0x48/0x12c
> l2cap_recv_frame+0x4770/0x6550
> l2cap_recv_acldata+0x44c/0x7a4
> hci_acldata_packet+0x100/0x188
> hci_rx_work+0x178/0x23c
> process_one_work+0x35c/0x95c
> worker_thread+0x4cc/0x960
> kthread+0x1a8/0x1c4
> ret_from_fork+0x10/0x18
>
> Cc: stable@xxxxxxxxxx
When was the bug added ? (Fixes: tag please)
> Cc: Marcel Holtmann <marcel@xxxxxxxxxxxx>
> Cc: Johan Hedberg <johan.hedberg@xxxxxxxxx>
> Cc: Luiz Augusto von Dentz <luiz.dentz@xxxxxxxxx>
> Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
> Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
> Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
> Cc: Paolo Abeni <pabeni@xxxxxxxxxx>
> Cc: linux-bluetooth@xxxxxxxxxxxxxxx
> Cc: netdev@xxxxxxxxxxxxxxx
> Signed-off-by: Lee Jones <lee.jones@xxxxxxxxxx>
> ---
> net/bluetooth/l2cap_core.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> index ae78490ecd3d4..82279c5919fd8 100644
> --- a/net/bluetooth/l2cap_core.c
> +++ b/net/bluetooth/l2cap_core.c
> @@ -483,9 +483,7 @@ static void l2cap_chan_destroy(struct kref *kref)
>
> BT_DBG("chan %p", chan);
>
> - write_lock(&chan_list_lock);
> list_del(&chan->global_l);
> - write_unlock(&chan_list_lock);
>
> kfree(chan);
> }
> @@ -501,7 +499,9 @@ void l2cap_chan_put(struct l2cap_chan *c)
> {
> BT_DBG("chan %p orig refcnt %u", c, kref_read(&c->kref));
>
> + write_lock(&chan_list_lock);
> kref_put(&c->kref, l2cap_chan_destroy);
> + write_unlock(&chan_list_lock);
> }
> EXPORT_SYMBOL_GPL(l2cap_chan_put);
>
> --
> 2.36.1.255.ge46751e96f-goog
>
I do not think this patch is correct.
a kref does not need to be protected by a write lock.
This might shuffle things enough to work around a particular repro you have.
If the patch was correct why not protect kref_get() sides ?
Before the &hdev->rx_work is scheduled (queue_work(hdev->workqueue,
&hdev->rx_work),
a reference must be taken.
Then this reference must be released at the end of hci_rx_work() or
when hdev->workqueue
is canceled.
This refcount is not needed _if_ the workqueue is properly canceled at
device dismantle,
in a synchronous way.
I do not see this hdev->rx_work being canceled, maybe this is the real issue.
There is a call to drain_workqueue() but this is not enough I think,
because hci_recv_frame()
can re-arm
queue_work(hdev->workqueue, &hdev->rx_work);
