hsr: switch ->dellink() to ->ndo_uninit()

Switching from ->priv_destructor to dellink() has an unexpected
consequence: existing RCU readers, that is, hsr_port_get_hsr()
callers, may still be able to read the port list.

Instead of checking the return value of each hsr_port_get_hsr(),
we can just move it to ->ndo_uninit() which is called after
device unregister and synchronize_net(), and we still have RTNL
lock there.

Fixes: b9a1e627405d ("hsr: implement dellink to clean up resources")
Fixes: edf070a0fb45 ("hsr: fix a NULL pointer deref in hsr_dev_xmit()")
Reported-by: syzbot+097ef84cdc95843fbaa8@syzkaller.appspotmail.com
Cc: Arvid Brodin <arvid.brodin@alten.se>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 8 insertions, 18 deletions

diff --git a/net/hsr/hsr_device.c b/net/hsr/hsr_device.c
index f0f9b493c47b..f509b495451a 100644
--- a/net/hsr/hsr_device.c
+++ b/net/hsr/hsr_device.c
@@ -227,13 +227,8 @@ static int hsr_dev_xmit(struct sk_buff *skb, struct net_device *dev)
         struct hsr_port *master;
 
         master = hsr_port_get_hsr(hsr, HSR_PT_MASTER);
-        if (master) {
-                skb->dev = master->dev;
-                hsr_forward_skb(skb, master);
-        } else {
-                atomic_long_inc(&dev->tx_dropped);
-                dev_kfree_skb_any(skb);
-        }
+        skb->dev = master->dev;
+        hsr_forward_skb(skb, master);
         return NETDEV_TX_OK;
 }
 
@@ -348,7 +343,11 @@ static void hsr_announce(struct timer_list *t)
         rcu_read_unlock();
 }
 
-void hsr_dev_destroy(struct net_device *hsr_dev)
+/* This has to be called after all the readers are gone.
+ * Otherwise we would have to check the return value of
+ * hsr_port_get_hsr().
+ */
+static void hsr_dev_destroy(struct net_device *hsr_dev)
 {
         struct hsr_priv *hsr;
         struct hsr_port *port;
@@ -364,8 +363,6 @@ void hsr_dev_destroy(struct net_device *hsr_dev)
         del_timer_sync(&hsr->prune_timer);
         del_timer_sync(&hsr->announce_timer);
 
-        synchronize_rcu();
-
         hsr_del_self_node(&hsr->self_node_db);
         hsr_del_nodes(&hsr->node_db);
 }
@@ -376,6 +373,7 @@ static const struct net_device_ops hsr_device_ops = {
         .ndo_stop = hsr_dev_close,
         .ndo_start_xmit = hsr_dev_xmit,
         .ndo_fix_features = hsr_fix_features,
+        .ndo_uninit = hsr_dev_destroy,
 };
 
 static struct device_type hsr_type = {
diff --git a/net/hsr/hsr_device.h b/net/hsr/hsr_device.h
index d0fa6b0696d2..6d7759c4f5f9 100644
--- a/net/hsr/hsr_device.h
+++ b/net/hsr/hsr_device.h
@@ -14,7 +14,6 @@
 void hsr_dev_setup(struct net_device *dev);
 int hsr_dev_finalize(struct net_device *hsr_dev, struct net_device *slave[2],
                      unsigned char multicast_spec, u8 protocol_version);
-void hsr_dev_destroy(struct net_device *hsr_dev);
 void hsr_check_carrier_and_operstate(struct hsr_priv *hsr);
 bool is_hsr_master(struct net_device *dev);
 int hsr_get_max_mtu(struct hsr_priv *hsr);
diff --git a/net/hsr/hsr_netlink.c b/net/hsr/hsr_netlink.c
index 160edd24de4e..8f8337f893ba 100644
--- a/net/hsr/hsr_netlink.c
+++ b/net/hsr/hsr_netlink.c
@@ -69,12 +69,6 @@ static int hsr_newlink(struct net *src_net, struct net_device *dev,
         return hsr_dev_finalize(dev, link, multicast_spec, hsr_version);
 }
 
-static void hsr_dellink(struct net_device *hsr_dev, struct list_head *head)
-{
-        hsr_dev_destroy(hsr_dev);
-        unregister_netdevice_queue(hsr_dev, head);
-}
-
 static int hsr_fill_info(struct sk_buff *skb, const struct net_device *dev)
 {
         struct hsr_priv *hsr;
@@ -119,7 +113,6 @@ static struct rtnl_link_ops hsr_link_ops __read_mostly = {
         .priv_size      = sizeof(struct hsr_priv),
         .setup          = hsr_dev_setup,
         .newlink        = hsr_newlink,
-        .dellink        = hsr_dellink,
         .fill_info      = hsr_fill_info,
 };