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USB: legousbtower: fix deadlock on disconnect 

Fix a potential deadlock if disconnect races with open.

Since commit d4ead16f50 ("USB: prevent char device open/deregister
race") core holds an rw-semaphore while open is called and when
releasing the minor number during deregistration. This can lead to an
ABBA deadlock if a driver takes a lock in open which it also holds
during deregistration.

This effectively reverts commit 78663ecc34 ("USB: disconnect open race
in legousbtower") which needlessly introduced this issue after a generic
fix for this race had been added to core by commit d4ead16f50 ("USB:
prevent char device open/deregister race").

Fixes: 78663ecc34 ("USB: disconnect open race in legousbtower")
Cc: stable <stable@vger.kernel.org>	# 2.6.24
Reported-by: syzbot+f9549f5ee8a5416f0b95@syzkaller.appspotmail.com
Tested-by: syzbot+f9549f5ee8a5416f0b95@syzkaller.appspotmail.com
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20190919083039.30898-3-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Johan Hovold 2019-09-19 10:30:37 +02:00 committed by Greg Kroah-Hartman
parent 1d427be4a3
commit 33a7813219
1 changed files with 2 additions and 17 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

19
drivers/usb/misc/legousbtower.c
View File

@ -179,7 +179,6 @@ static const struct usb_device_id tower_table[] = {
};
MODULE_DEVICE_TABLE (usb, tower_table);
static DEFINE_MUTEX(open_disc_mutex);
#define LEGO_USB_TOWER_MINOR_BASE 160
@ -332,18 +331,14 @@ static int tower_open (struct inode *inode, struct file *file)
goto exit;
}
mutex_lock(&open_disc_mutex);
dev = usb_get_intfdata(interface);
if (!dev) {
mutex_unlock(&open_disc_mutex);
retval = -ENODEV;
goto exit;
}
/* lock this device */
if (mutex_lock_interruptible(&dev->lock)) {
mutex_unlock(&open_disc_mutex);
retval = -ERESTARTSYS;
goto exit;
}
@ -351,12 +346,10 @@ static int tower_open (struct inode *inode, struct file *file)
/* allow opening only once */
if (dev->open_count) {
mutex_unlock(&open_disc_mutex);
retval = -EBUSY;
goto unlock_exit;
}
dev->open_count = 1;
mutex_unlock(&open_disc_mutex);
/* reset the tower */
result = usb_control_msg (dev->udev,
@ -423,10 +416,9 @@ static int tower_release (struct inode *inode, struct file *file)
if (dev == NULL) {
retval = -ENODEV;
goto exit_nolock;
goto exit;
}
mutex_lock(&open_disc_mutex);
if (mutex_lock_interruptible(&dev->lock)) {
retval = -ERESTARTSYS;
goto exit;
@ -456,10 +448,7 @@ static int tower_release (struct inode *inode, struct file *file)
unlock_exit:
mutex_unlock(&dev->lock);
exit:
mutex_unlock(&open_disc_mutex);
exit_nolock:
return retval;
}
@ -912,7 +901,6 @@ static int tower_probe (struct usb_interface *interface, const struct usb_device
if (retval) {
/* something prevented us from registering this driver */
dev_err(idev, "Not able to get a minor for this device.\n");
usb_set_intfdata (interface, NULL);
goto error;
}
dev->minor = interface->minor;
@ -944,16 +932,13 @@ static void tower_disconnect (struct usb_interface *interface)
int minor;
dev = usb_get_intfdata (interface);
mutex_lock(&open_disc_mutex);
usb_set_intfdata (interface, NULL);
minor = dev->minor;
/* give back our minor */
/* give back our minor and prevent further open() */
usb_deregister_dev (interface, &tower_class);
mutex_lock(&dev->lock);
mutex_unlock(&open_disc_mutex);
/* if the device is not opened, then we clean up right now */
if (!dev->open_count) {