uio: Fix use-after-free in uio_open

core-1				core-2
-------------------------------------------------------
uio_unregister_device		uio_open
				idev = idr_find()
device_unregister(&idev->dev)
put_device(&idev->dev)
uio_device_release
				get_device(&idev->dev)
kfree(idev)
uio_free_minor(minor)
				uio_release
				put_device(&idev->dev)
				kfree(idev)
-------------------------------------------------------

In the core-1 uio_unregister_device(), the device_unregister will kfree
idev when the idev->dev kobject ref is 1. But after core-1
device_unregister, put_device and before doing kfree, the core-2 may
get_device. Then:
1. After core-1 kfree idev, the core-2 will do use-after-free for idev.
2. When core-2 do uio_release and put_device, the idev will be double
   freed.

To address this issue, we can get idev atomic & inc idev reference with
minor_lock.

Fixes: 57c5f4df0a5a ("uio: fix crash after the device is unregistered")
Cc: stable <stable@kernel.org>
Signed-off-by: Guanghui Feng <guanghuifeng@linux.alibaba.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Link: https://lore.kernel.org/r/1703152663-59949-1-git-send-email-guanghuifeng@linux.alibaba.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c
index 62082d64ece00613a9d82eadd0552f6262cb9c10..2d572f6c8ec833023450136e3e2278d46d8937ae 100644 (file)
--- a/drivers/uio/uio.c
+++ b/drivers/uio/uio.c
@@ -466,13 +466,13 @@ static int uio_open(struct inode *inode, struct file *filep)
 
        mutex_lock(&minor_lock);
        idev = idr_find(&uio_idr, iminor(inode));
-       mutex_unlock(&minor_lock);
        if (!idev) {
                ret = -ENODEV;
+               mutex_unlock(&minor_lock);
                goto out;
        }
-
        get_device(&idev->dev);
+       mutex_unlock(&minor_lock);
 
        if (!try_module_get(idev->owner)) {
                ret = -ENODEV;
@@ -1064,9 +1064,8 @@ void uio_unregister_device(struct uio_info *info)
        wake_up_interruptible(&idev->wait);
        kill_fasync(&idev->async_queue, SIGIO, POLL_HUP);
 
-       device_unregister(&idev->dev);
-
        uio_free_minor(minor);
+       device_unregister(&idev->dev);
 
        return;
 }