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>

3 files changed, 11 insertions, 9 deletions

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index c79a88be7c33..fa8b47637997 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -2059,12 +2059,12 @@ static inline void skb_bond_set_mac_by_master(struct sk_buff *skb,
  * duplicates except for 802.3ad ETH_P_SLOW, alb non-mcast/bcast, and
  * ARP on active-backup slaves with arp_validate enabled.
  */
-static inline int skb_bond_should_drop(struct sk_buff *skb)
+static inline int skb_bond_should_drop(struct sk_buff *skb,
+                                       struct net_device *master)
 {
-        struct net_device *dev = skb->dev;
-        struct net_device *master = dev->master;
-
         if (master) {
+                struct net_device *dev = skb->dev;
+
                 if (master->priv_flags & IFF_MASTER_ARPMON)
                         dev->last_rx = jiffies;
 
diff --git a/net/8021q/vlan_core.c b/net/8021q/vlan_core.c
index c0316e0ca6e8..c584a0af77d3 100644
--- a/net/8021q/vlan_core.c
+++ b/net/8021q/vlan_core.c
@@ -11,7 +11,7 @@ int __vlan_hwaccel_rx(struct sk_buff *skb, struct vlan_group *grp,
         if (netpoll_rx(skb))
                 return NET_RX_DROP;
 
-        if (skb_bond_should_drop(skb))
+        if (skb_bond_should_drop(skb, ACCESS_ONCE(skb->dev->master)))
                 goto drop;
 
         skb->skb_iif = skb->dev->ifindex;
@@ -83,7 +83,7 @@ vlan_gro_common(struct napi_struct *napi, struct vlan_group *grp,
 {
         struct sk_buff *p;
 
-        if (skb_bond_should_drop(skb))
+        if (skb_bond_should_drop(skb, ACCESS_ONCE(skb->dev->master)))
                 goto drop;
 
         skb->skb_iif = skb->dev->ifindex;
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++;