arp: fix possible crash in arp_rcv()

We should call skb_share_check() before pskb_may_pull(), or we
can crash in pskb_expand_head()

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 11 insertions, 10 deletions

diff --git a/net/ipv4/arp.c b/net/ipv4/arp.c
index 9547a273b9e9..ded146b217f1 100644
--- a/net/ipv4/arp.c
+++ b/net/ipv4/arp.c
@@ -928,24 +928,25 @@ static void parp_redo(struct sk_buff *skb)
 static int arp_rcv(struct sk_buff *skb, struct net_device *dev,
                    struct packet_type *pt, struct net_device *orig_dev)
 {
-        struct arphdr *arp;
+        const struct arphdr *arp;
+
+        if (dev->flags & IFF_NOARP ||
+            skb->pkt_type == PACKET_OTHERHOST ||
+            skb->pkt_type == PACKET_LOOPBACK)
+                goto freeskb;
+
+        skb = skb_share_check(skb, GFP_ATOMIC);
+        if (!skb)
+                goto out_of_mem;
 
         /* ARP header, plus 2 device addresses, plus 2 IP addresses.  */
         if (!pskb_may_pull(skb, arp_hdr_len(dev)))
                 goto freeskb;
 
         arp = arp_hdr(skb);
-        if (arp->ar_hln != dev->addr_len ||
-            dev->flags & IFF_NOARP ||
-            skb->pkt_type == PACKET_OTHERHOST ||
-            skb->pkt_type == PACKET_LOOPBACK ||
-            arp->ar_pln != 4)
+        if (arp->ar_hln != dev->addr_len || arp->ar_pln != 4)
                 goto freeskb;
 
-        skb = skb_share_check(skb, GFP_ATOMIC);
-        if (skb == NULL)
-                goto out_of_mem;
-
         memset(NEIGH_CB(skb), 0, sizeof(struct neighbour_cb));
 
         return NF_HOOK(NFPROTO_ARP, NF_ARP_IN, skb, dev, NULL, arp_process);