tuntap: fix leaking reference count

Reference count leaking of both module and sock were found:

- When a detached file were closed, its sock refcnt from device were not
  released, solving this by add the sock_put().
- The module were hold or drop unconditionally in TUNSETPERSIST, which means we
  if we set the persist flag for N times, we need unset it for another N
  times. Solving this by only hold or drop an reference when there's a flag
  change and also drop the reference count when the persist device is deleted.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 9 insertions, 3 deletions

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index a36b56f0940b..af372d0957fe 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -428,8 +428,10 @@ static void __tun_detach(struct tun_file *tfile, bool clean)
                 /* Drop read queue */
                 skb_queue_purge(&tfile->sk.sk_receive_queue);
                 tun_set_real_num_queues(tun);
-        } else if (tfile->detached && clean)
+        } else if (tfile->detached && clean) {
                 tun = tun_enable_queue(tfile);
+                sock_put(&tfile->sk);
+        }
 
         if (clean) {
                 if (tun && tun->numqueues == 0 && tun->numdisabled == 0 &&
@@ -478,6 +480,9 @@ static void tun_detach_all(struct net_device *dev)
                 sock_put(&tfile->sk);
         }
         BUG_ON(tun->numdisabled != 0);
+
+        if (tun->flags & TUN_PERSIST)
+                module_put(THIS_MODULE);
 }
 
 static int tun_attach(struct tun_struct *tun, struct file *file)
@@ -1874,10 +1879,11 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
                 /* Disable/Enable persist mode. Keep an extra reference to the
                  * module to prevent the module being unprobed.
                  */
-                if (arg) {
+                if (arg && !(tun->flags & TUN_PERSIST)) {
                         tun->flags |= TUN_PERSIST;
                         __module_get(THIS_MODULE);
-                } else {
+                }
+                if (!arg && (tun->flags & TUN_PERSIST)) {
                         tun->flags &= ~TUN_PERSIST;
                         module_put(THIS_MODULE);
                 }