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USB: appledisplay: fix race between reading and writing from the device 

The workqueue handler may call appledisplay_bl_get_brightness() while
user space calls appledisplay_bl_update_status(). As they share a
buffer that must not happen. Use a mutex for mutual exclusion.

Signed-off-by: Oliver Neukum <oneukum@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Oliver Neukum 2014-05-19 13:53:55 +02:00 committed by Greg Kroah-Hartman
parent d846b7650d
commit 552e1f2679
1 changed files with 10 additions and 3 deletions
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13
drivers/usb/misc/appledisplay.c
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@ -81,6 +81,7 @@ struct appledisplay {
struct delayed_work work;
int button_pressed;
spinlock_t lock;
struct mutex sysfslock; /* concurrent read and write */
};
static atomic_t count_displays = ATOMIC_INIT(0);
@ -144,6 +145,7 @@ static int appledisplay_bl_update_status(struct backlight_device *bd)
struct appledisplay *pdata = bl_get_data(bd);
int retval;
mutex_lock(&pdata->sysfslock);
pdata->msgdata[0] = 0x10;
pdata->msgdata[1] = bd->props.brightness;
@ -156,15 +158,17 @@ static int appledisplay_bl_update_status(struct backlight_device *bd)
0,
pdata->msgdata, 2,
ACD_USB_TIMEOUT);
mutex_unlock(&pdata->sysfslock);
return retval;
}
static int appledisplay_bl_get_brightness(struct backlight_device *bd)
{
struct appledisplay *pdata = bl_get_data(bd);
int retval;
int retval, brightness;
mutex_lock(&pdata->sysfslock);
retval = usb_control_msg(
pdata->udev,
usb_rcvctrlpipe(pdata->udev, 0),
@ -174,11 +178,13 @@ static int appledisplay_bl_get_brightness(struct backlight_device *bd)
0,
pdata->msgdata, 2,
ACD_USB_TIMEOUT);
brightness = pdata->msgdata[1];
mutex_unlock(&pdata->sysfslock);
if (retval < 0)
return retval;
else
return pdata->msgdata[1];
return brightness;
}
static const struct backlight_ops appledisplay_bl_data = {
@ -241,6 +247,7 @@ static int appledisplay_probe(struct usb_interface *iface,
spin_lock_init(&pdata->lock);
INIT_DELAYED_WORK(&pdata->work, appledisplay_work);
mutex_init(&pdata->sysfslock);
/* Allocate buffer for control messages */
pdata->msgdata = kmalloc(ACD_MSG_BUFFER_LEN, GFP_KERNEL);