3.16.80-rc1 review patch. If anyone has any objections, please let me know.
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From: Johan Hovold johan@kernel.org
commit 33a7813219f208f4952ece60ee255fd983272dec upstream.
Fix a potential deadlock if disconnect races with open.
Since commit d4ead16f50f9 ("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 78663ecc344b ("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 d4ead16f50f9 ("USB: prevent char device open/deregister race").
Fixes: 78663ecc344b ("USB: disconnect open race in legousbtower") 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 Signed-off-by: Ben Hutchings ben@decadent.org.uk --- drivers/usb/misc/legousbtower.c | 19 ++----------------- 1 file changed, 2 insertions(+), 17 deletions(-)
--- a/drivers/usb/misc/legousbtower.c +++ b/drivers/usb/misc/legousbtower.c @@ -185,7 +185,6 @@ static const struct usb_device_id tower_ };
MODULE_DEVICE_TABLE (usb, tower_table); -static DEFINE_MUTEX(open_disc_mutex);
#define LEGO_USB_TOWER_MINOR_BASE 160
@@ -338,18 +337,14 @@ static int tower_open (struct inode *ino 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; } @@ -357,12 +352,10 @@ static int tower_open (struct inode *ino
/* 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, @@ -429,10 +422,9 @@ static int tower_release (struct inode *
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; @@ -462,10 +454,7 @@ static int tower_release (struct inode *
unlock_exit: mutex_unlock(&dev->lock); - exit: - mutex_unlock(&open_disc_mutex); -exit_nolock: return retval; }
@@ -944,7 +933,6 @@ static int tower_probe (struct usb_inter 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; @@ -976,16 +964,13 @@ static void tower_disconnect (struct usb 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) {