net: Potential null skb->dev dereference

When doing "ifenslave -d bond0 eth0", there is chance to get NULL
dereference in netif_receive_skb(), because dev->master suddenly becomes
NULL after we tested it.

We should use ACCESS_ONCE() to avoid this (or rcu_dereference())

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 3 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index bcc490cc9452..59d4394d2ce8 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2483,6 +2483,7 @@ int netif_receive_skb(struct sk_buff *skb)
 {
         struct packet_type *ptype, *pt_prev;
         struct net_device *orig_dev;
+        struct net_device *master;
         struct net_device *null_or_orig;
         struct net_device *null_or_bond;
         int ret = NET_RX_DROP;
@@ -2503,11 +2504,12 @@ int netif_receive_skb(struct sk_buff *skb)
 
         null_or_orig = NULL;
         orig_dev = skb->dev;
-        if (orig_dev->master) {
-                if (skb_bond_should_drop(skb))
+        master = ACCESS_ONCE(orig_dev->master);
+        if (master) {
+                if (skb_bond_should_drop(skb, master))
                         null_or_orig = orig_dev; /* deliver only exact match */
                 else
-                        skb->dev = orig_dev->master;
+                        skb->dev = master;
         }
 
         __get_cpu_var(netdev_rx_stat).total++;