[PATCH 4.6 08/81] tuntap: correctly wake up process during uninit

Greg Kroah-Hartman
2016-06-22T23:05:10Z

From: Jason Wang <jasowang@redhat.com>

[ Upstream commit addf8fc4acb1cf79492ac64966f07178793cb3d7 ]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/net/tun.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -568,11 +568,13 @@ static void tun_detach_all(struct net_de
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);
}
@@ -628,6 +630,7 @@ static int tun_attach(struct tun_struct
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++;
@@ -1425,9 +1428,6 @@ static ssize_t tun_do_read(struct tun_st
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);