usbip: vudc synchronize sysfs code paths

Fuzzing uncovered race condition between sysfs code paths in usbip
drivers. Device connect/disconnect code paths initiated through
sysfs interface are prone to races if disconnect happens during
connect and vice versa.

Use sysfs_lock to protect sysfs paths in vudc.

Cc: stable@vger.kernel.org
Reported-and-tested-by: syzbot+a93fba6d384346a761e3@syzkaller.appspotmail.com
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Link: https://lore.kernel.org/r/caabcf3fc87bdae970509b5ff32d05bb7ce2fb15.1616807117.git.skhan@linuxfoundation.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/usbip/vudc_dev.c

@@ -572,6 +572,7 @@ static int init_vudc_hw(struct vudc *udc)
 	init_waitqueue_head(&udc->tx_waitq);
 
 	spin_lock_init(&ud->lock);
+	mutex_init(&ud->sysfs_lock);
 	ud->status = SDEV_ST_AVAILABLE;
 	ud->side = USBIP_VUDC;
 

drivers/usb/usbip/vudc_sysfs.c

@@ -112,6 +112,7 @@ static ssize_t usbip_sockfd_store(struct device *dev,
 		dev_err(dev, "no device");
 		return -ENODEV;
 	}
+	mutex_lock(&udc->ud.sysfs_lock);
 	spin_lock_irqsave(&udc->lock, flags);
 	/* Don't export what we don't have */
 	if (!udc->driver || !udc->pullup) {
@@ -187,6 +188,8 @@ static ssize_t usbip_sockfd_store(struct device *dev,
 
 		wake_up_process(udc->ud.tcp_rx);
 		wake_up_process(udc->ud.tcp_tx);
+
+		mutex_unlock(&udc->ud.sysfs_lock);
 		return count;
 
 	} else {
@@ -207,6 +210,7 @@ static ssize_t usbip_sockfd_store(struct device *dev,
 	}
 
 	spin_unlock_irqrestore(&udc->lock, flags);
+	mutex_unlock(&udc->ud.sysfs_lock);
 
 	return count;
 
@@ -216,6 +220,7 @@ static ssize_t usbip_sockfd_store(struct device *dev,
 	spin_unlock_irq(&udc->ud.lock);
 unlock:
 	spin_unlock_irqrestore(&udc->lock, flags);
+	mutex_unlock(&udc->ud.sysfs_lock);
 
 	return ret;
 }