[PATCH] HID: elo: Fix refcount leak in elo_probe()

[Alan Stern <stern@rowland.harvard.edu>]

Syzbot identified a refcount leak in the hid-elo driver:

BUG: memory leak
unreferenced object 0xffff88810d49e800 (size 2048):
  comm "kworker/1:1", pid 25, jiffies 4294954629 (age 16.460s)
  hex dump (first 32 bytes):
    ff ff ff ff 31 00 00 00 00 00 00 00 00 00 00 00  ....1...........
    00 00 00 00 00 00 00 00 00 00 00 00 03 00 00 00  ................
  backtrace:
    [<ffffffff82c87a62>] kmalloc include/linux/slab.h:581 [inline]
    [<ffffffff82c87a62>] kzalloc include/linux/slab.h:715 [inline]
    [<ffffffff82c87a62>] usb_alloc_dev+0x32/0x450 drivers/usb/core/usb.c:582
    [<ffffffff82c91a47>] hub_port_connect drivers/usb/core/hub.c:5260 [inline]
    [<ffffffff82c91a47>] hub_port_connect_change drivers/usb/core/hub.c:5502 [inline]
    [<ffffffff82c91a47>] port_event drivers/usb/core/hub.c:5660 [inline]
    [<ffffffff82c91a47>] hub_event+0x1097/0x21a0 drivers/usb/core/hub.c:5742
    [<ffffffff8126c3ef>] process_one_work+0x2bf/0x600 kernel/workqueue.c:2307
    [<ffffffff8126ccd9>] worker_thread+0x59/0x5b0 kernel/workqueue.c:2454
    [<ffffffff81276765>] kthread+0x125/0x160 kernel/kthread.c:377
    [<ffffffff810022ff>] ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

Not shown in the bug report but present in the console log:

[  182.014764][ T3257] elo 0003:04E7:0030.0006: item fetching failed at offset 0/1
[  182.022255][ T3257] elo 0003:04E7:0030.0006: parse failed
[  182.027904][ T3257] elo: probe of 0003:04E7:0030.0006 failed with error -22
[  182.214767][ T3257] usb 1-1: USB disconnect, device number 7
[  188.090199][ T3604] kmemleak: 3 new suspected memory leaks (see /sys/kernel/debug/kmemleak)
BUG: memory leak

which points to hid-elo as the buggy driver.

The leak is caused by elo_probe() failing to release the reference it
holds to the struct usb_device in its failure pathway.  In the end the
driver doesn't need to take this reference at all, because the
elo_priv structure is always deallocated synchronously when the driver
unbinds from the interface.

Therefore this patch fixes the reference leak by not taking the
reference in the first place.

Reported-and-tested-by: syzbot+8caaaec4e7a55d75e243@syzkaller.appspotmail.com
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
CC: <stable@vger.kernel.org>

---


[as1971]


 drivers/hid/hid-elo.c |    4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

Index: usb-devel/drivers/hid/hid-elo.c
===================================================================
--- usb-devel.orig/drivers/hid/hid-elo.c
+++ usb-devel/drivers/hid/hid-elo.c
@@ -239,7 +239,7 @@ static int elo_probe(struct hid_device *
 
 	INIT_DELAYED_WORK(&priv->work, elo_work);
 	udev = interface_to_usbdev(to_usb_interface(hdev->dev.parent));
-	priv->usbdev = usb_get_dev(udev);
+	priv->usbdev = udev;
 
 	hid_set_drvdata(hdev, priv);
 
@@ -270,8 +270,6 @@ static void elo_remove(struct hid_device
 {
 	struct elo_priv *priv = hid_get_drvdata(hdev);
 
-	usb_put_dev(priv->usbdev);
-
 	hid_hw_stop(hdev);
 	cancel_delayed_work_sync(&priv->work);
 	kfree(priv);