Hi, On Wed, Jul 6, 2022 at 1:36 PM Luiz Augusto von Dentz wrote: > > Hi Lee, > > On Wed, Jul 6, 2022 at 3:53 AM Lee Jones wrote: > > > > On Tue, 05 Jul 2022, Luiz Augusto von Dentz wrote: > > > > > Hi Lee, > > > > > > On Wed, Jun 29, 2022 at 8:28 AM Lee Jones wrote: > > > > > > > > On Tue, 28 Jun 2022, Luiz Augusto von Dentz wrote: > > > > > > > > > Hi Eric, Lee, > > > > > > > > > > On Mon, Jun 27, 2022 at 4:39 PM Luiz Augusto von Dentz > > > > > wrote: > > > > > > > > > > > > Hi Eric, Lee, > > > > > > > > > > > > On Mon, Jun 27, 2022 at 7:41 AM Eric Dumazet wrote: > > > > > > > > > > > > > > On Wed, Jun 22, 2022 at 10:27 AM Lee Jones 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@kernel.org > > > > > > > > > > > > > > When was the bug added ? (Fixes: tag please) > > > > > > > > > > > > > > > Cc: Marcel Holtmann > > > > > > > > Cc: Johan Hedberg > > > > > > > > Cc: Luiz Augusto von Dentz > > > > > > > > Cc: "David S. Miller" > > > > > > > > Cc: Eric Dumazet > > > > > > > > Cc: Jakub Kicinski > > > > > > > > Cc: Paolo Abeni > > > > > > > > Cc: linux-bluetooth@vger.kernel.org > > > > > > > > Cc: netdev@vger.kernel.org > > > > > > > > Signed-off-by: Lee Jones > > > > > > > > --- > > > > > > > > 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); > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > 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); > > > > > > > > > > > > I suspect this likely a refcount problem, we do l2cap_get_chan_by_scid: > > > > > > > > > > > > /* Find channel with given SCID. > > > > > > * Returns locked channel. */ > > > > > > static struct l2cap_chan *l2cap_get_chan_by_scid(struct l2cap_conn > > > > > > *conn, u16 cid) > > > > > > > > > > > > So we return a locked channel but that doesn't prevent another thread > > > > > > to call l2cap_chan_put which doesn't care about l2cap_chan_lock so > > > > > > perhaps we actually need to host a reference while we have the lock, > > > > > > at least we do something like that on l2cap_sock.c: > > > > > > > > > > > > l2cap_chan_hold(chan); > > > > > > l2cap_chan_lock(chan); > > > > > > > > > > > > __clear_chan_timer(chan); > > > > > > l2cap_chan_close(chan, ECONNRESET); > > > > > > l2cap_sock_kill(sk); > > > > > > > > > > > > l2cap_chan_unlock(chan); > > > > > > l2cap_chan_put(chan); > > > > > > > > > > Perhaps something like this: > > > > > > > > I'm struggling to apply this for test: > > > > > > > > "error: corrupt patch at line 6" > > > > > > Check with the attached patch. > > > > With the patch applied: > > > > [ 188.825418][ T75] refcount_t: addition on 0; use-after-free. > > [ 188.825418][ T75] refcount_t: addition on 0; use-after-free. > > Looks like the changes just make the issue more visible since we are > trying to add a refcount when it is already 0 so this proves the > design is not quite right since it is removing the object from the > list only when destroying it while we probably need to do it before. > > How about we use kref_get_unless_zero as it appears it was introduced > exactly for such cases (patch attached.) Looks like I missed a few places like l2cap_global_chan_by_psm so here is another version. > Luiz Augusto von Dentz -- Luiz Augusto von Dentz