net, ipv6: convert inet6_dev.refcnt from atomic_t to refcount_t

refcount_t type and corresponding API should be
used instead of atomic_t when the variable is used as
a reference counter. This allows to avoid accidental
refcounter overflows that might lead to use-after-free
situations.

Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David Windsor <dwindsor@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 114fb64..2365f12 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -426,7 +426,7 @@ static struct inet6_dev *ipv6_add_dev(struct net_device *dev)
 	}
 
 	/* One reference from device. */
-	in6_dev_hold(ndev);
+	refcount_set(&ndev->refcnt, 1);
 
 	if (dev->flags & (IFF_NOARP | IFF_LOOPBACK))
 		ndev->cnf.accept_dad = -1;