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Subject[PATCH 3.16 087/157] staging: comedi: vmk80xx: Fix use of uninitialized semaphore
3.16.72-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Ian Abbott <abbotti@mev.co.uk>

commit 08b7c2f9208f0e2a32159e4e7a4831b7adb10a3e upstream.

If `vmk80xx_auto_attach()` returns an error, the core comedi module code
will call `vmk80xx_detach()` to clean up. If `vmk80xx_auto_attach()`
successfully allocated the comedi device private data,
`vmk80xx_detach()` assumes that a `struct semaphore limit_sem` contained
in the private data has been initialized and uses it. Unfortunately,
there are a couple of places where `vmk80xx_auto_attach()` can return an
error after allocating the device private data but before initializing
the semaphore, so this assumption is invalid. Fix it by initializing
the semaphore just after allocating the private data in
`vmk80xx_auto_attach()` before any other errors can be returned.

I believe this was the cause of the following syzbot crash report
<https://syzkaller.appspot.com/bug?extid=54c2f58f15fe6876b6ad>:

usb 1-1: config 0 has no interface number 0
usb 1-1: New USB device found, idVendor=10cf, idProduct=8068, bcdDevice=e6.8d
usb 1-1: New USB device strings: Mfr=0, Product=0, SerialNumber=0
usb 1-1: config 0 descriptor??
vmk80xx 1-1:0.117: driver 'vmk80xx' failed to auto-configure device.
INFO: trying to register non-static key.
the code is fine but needs lockdep annotation.
turning off the locking correctness validator.
CPU: 0 PID: 12 Comm: kworker/0:1 Not tainted 5.1.0-rc4-319354-g9a33b36 #3
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: usb_hub_wq hub_event
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0xe8/0x16e lib/dump_stack.c:113
assign_lock_key kernel/locking/lockdep.c:786 [inline]
register_lock_class+0x11b8/0x1250 kernel/locking/lockdep.c:1095
__lock_acquire+0xfb/0x37c0 kernel/locking/lockdep.c:3582
lock_acquire+0x10d/0x2f0 kernel/locking/lockdep.c:4211
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
_raw_spin_lock_irqsave+0x44/0x60 kernel/locking/spinlock.c:152
down+0x12/0x80 kernel/locking/semaphore.c:58
vmk80xx_detach+0x59/0x100 drivers/staging/comedi/drivers/vmk80xx.c:829
comedi_device_detach+0xed/0x800 drivers/staging/comedi/drivers.c:204
comedi_device_cleanup.part.0+0x68/0x140 drivers/staging/comedi/comedi_fops.c:156
comedi_device_cleanup drivers/staging/comedi/comedi_fops.c:187 [inline]
comedi_free_board_dev.part.0+0x16/0x90 drivers/staging/comedi/comedi_fops.c:190
comedi_free_board_dev drivers/staging/comedi/comedi_fops.c:189 [inline]
comedi_release_hardware_device+0x111/0x140 drivers/staging/comedi/comedi_fops.c:2880
comedi_auto_config.cold+0x124/0x1b0 drivers/staging/comedi/drivers.c:1068
usb_probe_interface+0x31d/0x820 drivers/usb/core/driver.c:361
really_probe+0x2da/0xb10 drivers/base/dd.c:509
driver_probe_device+0x21d/0x350 drivers/base/dd.c:671
__device_attach_driver+0x1d8/0x290 drivers/base/dd.c:778
bus_for_each_drv+0x163/0x1e0 drivers/base/bus.c:454
__device_attach+0x223/0x3a0 drivers/base/dd.c:844
bus_probe_device+0x1f1/0x2a0 drivers/base/bus.c:514
device_add+0xad2/0x16e0 drivers/base/core.c:2106
usb_set_configuration+0xdf7/0x1740 drivers/usb/core/message.c:2021
generic_probe+0xa2/0xda drivers/usb/core/generic.c:210
usb_probe_device+0xc0/0x150 drivers/usb/core/driver.c:266
really_probe+0x2da/0xb10 drivers/base/dd.c:509
driver_probe_device+0x21d/0x350 drivers/base/dd.c:671
__device_attach_driver+0x1d8/0x290 drivers/base/dd.c:778
bus_for_each_drv+0x163/0x1e0 drivers/base/bus.c:454
__device_attach+0x223/0x3a0 drivers/base/dd.c:844
bus_probe_device+0x1f1/0x2a0 drivers/base/bus.c:514
device_add+0xad2/0x16e0 drivers/base/core.c:2106
usb_new_device.cold+0x537/0xccf drivers/usb/core/hub.c:2534
hub_port_connect drivers/usb/core/hub.c:5089 [inline]
hub_port_connect_change drivers/usb/core/hub.c:5204 [inline]
port_event drivers/usb/core/hub.c:5350 [inline]
hub_event+0x138e/0x3b00 drivers/usb/core/hub.c:5432
process_one_work+0x90f/0x1580 kernel/workqueue.c:2269
worker_thread+0x9b/0xe20 kernel/workqueue.c:2415
kthread+0x313/0x420 kernel/kthread.c:253
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:352

Reported-by: syzbot+54c2f58f15fe6876b6ad@syzkaller.appspotmail.com
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/staging/comedi/drivers/vmk80xx.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/staging/comedi/drivers/vmk80xx.c
+++ b/drivers/staging/comedi/drivers/vmk80xx.c
@@ -872,6 +872,8 @@ static int vmk80xx_auto_attach(struct co

devpriv->model = boardinfo->model;

+ sema_init(&devpriv->limit_sem, 8);
+
ret = vmk80xx_find_usb_endpoints(dev);
if (ret)
return ret;
@@ -880,8 +882,6 @@ static int vmk80xx_auto_attach(struct co
if (ret)
return ret;

- sema_init(&devpriv->limit_sem, 8);
-
usb_set_intfdata(intf, devpriv);

if (devpriv->model == VMK8061_MODEL) {
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