USB: legousbtower: fix deadlock on disconnect

BugLink: https://bugs.launchpad.net/bugs/1850541
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")
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>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

diff --git a/drivers/usb/misc/legousbtower.c b/drivers/usb/misc/legousbtower.c
index 798008cfbbd6644994e68e1869be9c38f3e0bcb0..22fce15ff8699cb8959b858c23e93103f33e10b3 100644 (file)
--- a/drivers/usb/misc/legousbtower.c
+++ b/drivers/usb/misc/legousbtower.c
@@ -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;
 }
 
@@ -911,7 +900,6 @@ 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;
@@ -943,16 +931,13 @@ 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) {