[PATCH 5.4 093/152] HID: hiddev: Fix race in in hiddev_disconnect()

Greg Kroah-Hartman
2020-03-03T18:05:57Z

From: dan.carpenter@oracle.com <dan.carpenter@oracle.com>

commit 5c02c447eaeda29d3da121a2e17b97ccaf579b51 upstream.

Syzbot reports that "hiddev" is used after it's free in hiddev_disconnect().
The hiddev_disconnect() function sets "hiddev->exist = 0;" so
hiddev_release() can free it as soon as we drop the "existancelock"
lock. This patch moves the mutex_unlock(&hiddev->existancelock) until
after we have finished using it.

Reported-by: syzbot+784ccb935f9900cc7c9e@syzkaller.appspotmail.com
Fixes: 7f77897ef2b6 ("HID: hiddev: fix potential use-after-free")
Suggested-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/hid/usbhid/hiddev.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/hid/usbhid/hiddev.c
+++ b/drivers/hid/usbhid/hiddev.c
@@ -941,9 +941,9 @@ void hiddev_disconnect(struct hid_device
hiddev->exist = 0;

if (hiddev->open) {
- mutex_unlock(&hiddev->existancelock);
hid_hw_close(hiddev->hid);
wake_up_interruptible(&hiddev->wait);
+ mutex_unlock(&hiddev->existancelock);
} else {
mutex_unlock(&hiddev->existancelock);
kfree(hiddev);