tuntap: forbid calling TUNSETIFF when detached

Michael points out that even after Stefan's fix the TUNSETIFF is still allowed
to create a new tap device. This because we only check tfile->tun but the
tfile->detached were introduced. Fix this by failing early in tun_set_iff() if
the file is detached. After this fix, there's no need to do the check again in
tun_set_iff(), so this patch removes it.

Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 2 deletions

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index aa963c44450a..a36b56f0940b 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -488,8 +488,6 @@ static int tun_attach(struct tun_struct *tun, struct file *file)
         err = -EINVAL;
         if (rtnl_dereference(tfile->tun))
                 goto out;
-        if (tfile->detached && tun != tfile->detached)
-                goto out;
 
         err = -EBUSY;
         if (!(tun->flags & TUN_TAP_MQ) && tun->numqueues == 1)
@@ -1543,6 +1541,9 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr)
         struct net_device *dev;
         int err;
 
+        if (tfile->detached)
+                return -EINVAL;
+
         dev = __dev_get_by_name(net, ifr->ifr_name);
         if (dev) {
                 if (ifr->ifr_flags & IFF_TUN_EXCL)