[PATCH] usb: hub: Fix unbalanced reference count and memory leak

[Viresh Kumar]

If the hub gets disconnected while the core is still activating it, this
can result in leaking memory of few USB structures.

This will happen if we have done a kref_get() from hub_activate() and
scheduled a delayed work item for HUB_INIT2/3. Now if hub_disconnect()
gets called before the delayed work expires, then we will cancel the
work from hub_quiesce(), but wouldn't do a kref_put(). And so the
unbalance.

kmemleak reports this as (with the commit e50293ef9775 backported to
3.10 kernel with other changes, though the same is true for mainline as
well):

unreferenced object 0xffffffc08af5b800 (size 1024):
  comm "khubd", pid 73, jiffies 4295051211 (age 6482.350s)
  hex dump (first 32 bytes):
    30 68 f3 8c c0 ff ff ff 00 a0 b2 2e c0 ff ff ff  0h..............
    01 00 00 00 00 00 00 00 00 94 7d 40 c0 ff ff ff  ..........}@....
  backtrace:
    [<ffffffc0003079ec>] create_object+0x148/0x2a0
    [<ffffffc000cc150c>] kmemleak_alloc+0x80/0xbc
    [<ffffffc000303a7c>] kmem_cache_alloc_trace+0x120/0x1ac
    [<ffffffc0006fa610>] hub_probe+0x120/0xb84
    [<ffffffc000702b20>] usb_probe_interface+0x1ec/0x298
    [<ffffffc0005d50cc>] driver_probe_device+0x160/0x374
    [<ffffffc0005d5308>] __device_attach+0x28/0x4c
    [<ffffffc0005d3164>] bus_for_each_drv+0x78/0xac
    [<ffffffc0005d4ee0>] device_attach+0x6c/0x9c
    [<ffffffc0005d42b8>] bus_probe_device+0x28/0xa0
    [<ffffffc0005d23a4>] device_add+0x324/0x604
    [<ffffffc000700fcc>] usb_set_configuration+0x660/0x6cc
    [<ffffffc00070a350>] generic_probe+0x44/0x84
    [<ffffffc000702914>] usb_probe_device+0x54/0x74
    [<ffffffc0005d50cc>] driver_probe_device+0x160/0x374
    [<ffffffc0005d5308>] __device_attach+0x28/0x4c

Fix this by putting the reference in hub_quiesce() if we canceled a
pending work.

CC: <stable@xxxxxxxxxxxxxxx> #4.4+
Fixes: e50293ef9775 ("USB: fix invalid memory access in hub_activate()")
Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
---
Greg,

This is tested over 3.10 with backported patches only, sorry didn't had
a mainline setup to test this out. :(

 drivers/usb/core/hub.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index bee13517676f..3173693fa8e3 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -1315,7 +1315,8 @@ static void hub_quiesce(struct usb_hub *hub, enum hub_quiescing_type type)
 	struct usb_device *hdev = hub->hdev;
 	int i;
 
-	cancel_delayed_work_sync(&hub->init_work);
+	if (cancel_delayed_work_sync(&hub->init_work))
+		kref_put(&hub->kref, hub_release);
 
 	/* hub_wq and related activity won't re-trigger */
 	hub->quiescing = 1;
-- 
2.7.4