tuntap: correctly wake up process during uninit

We used to check dev->reg_state against NETREG_REGISTERED after each
time we are woke up. But after commit 9e641bdcfa4e ("net-tun:
restructure tun_do_read for better sleep/wakeup efficiency"), it uses
skb_recv_datagram() which does not check dev->reg_state. This will
result if we delete a tun/tap device after a process is blocked in the
reading. The device will wait for the reference count which was held
by that process for ever.

Fixes this by using RCV_SHUTDOWN which will be checked during
sk_recv_datagram() before trying to wake up the process during uninit.

Fixes: 9e641bdcfa4e ("net-tun: restructure tun_do_read for better
sleep/wakeup efficiency")
Cc: Eric Dumazet <edumazet@google.com>
Cc: Xi Wang <xii@google.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 3 deletions

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 425e983bab93..e16487cc6a9a 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -580,11 +580,13 @@ static void tun_detach_all(struct net_device *dev)
         for (i = 0; i < n; i++) {
                 tfile = rtnl_dereference(tun->tfiles[i]);
                 BUG_ON(!tfile);
+                tfile->socket.sk->sk_shutdown = RCV_SHUTDOWN;
                 tfile->socket.sk->sk_data_ready(tfile->socket.sk);
                 RCU_INIT_POINTER(tfile->tun, NULL);
                 --tun->numqueues;
         }
         list_for_each_entry(tfile, &tun->disabled, next) {
+                tfile->socket.sk->sk_shutdown = RCV_SHUTDOWN;
                 tfile->socket.sk->sk_data_ready(tfile->socket.sk);
                 RCU_INIT_POINTER(tfile->tun, NULL);
         }
@@ -641,6 +643,7 @@ static int tun_attach(struct tun_struct *tun, struct file *file, bool skip_filte
                         goto out;
         }
         tfile->queue_index = tun->numqueues;
+        tfile->socket.sk->sk_shutdown &= ~RCV_SHUTDOWN;
         rcu_assign_pointer(tfile->tun, tun);
         rcu_assign_pointer(tun->tfiles[tun->numqueues], tfile);
         tun->numqueues++;
@@ -1491,9 +1494,6 @@ static ssize_t tun_do_read(struct tun_struct *tun, struct tun_file *tfile,
         if (!iov_iter_count(to))
                 return 0;
 
-        if (tun->dev->reg_state != NETREG_REGISTERED)
-                return -EIO;
-
         /* Read frames from queue */
         skb = __skb_recv_datagram(tfile->socket.sk, noblock ? MSG_DONTWAIT : 0,
                                   &peeked, &off, &err);