datapath: fix a use after free

pskb_may_pull() called by arphdr_ok can change skb->data, so put the arp
setting after arphdr_ok to avoid the use the freed memory

Fixes: 0714812134d7d ("openvswitch: Eliminate memset() from flow_extract.")
Cc: Jesse Gross <jesse@nicira.com>
Cc: Eric Dumazet <edumazet@google.com>
Signed-off-by: Li RongQing <roy.qing.li@gmail.com>
Acked-by: Jesse Gross <jesse@nicira.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
arphdr_ok() was not done on branch-2.3, so backported whole fix
as part of this patch.

Acked-by: Pravin B Shelar <pshelar@nicira.com>

diff --git a/datapath/flow.c b/datapath/flow.c
index ee835d1..e0cb720 100644 (file)
--- a/datapath/flow.c
+++ b/datapath/flow.c
@@ -539,15 +539,16 @@ static int key_extract(struct sk_buff *skb, struct sw_flow_key *key)
 
        } else if ((key->eth.type == htons(ETH_P_ARP) ||
                   key->eth.type == htons(ETH_P_RARP)) && arphdr_ok(skb)) {
+               bool arp_available = arphdr_ok(skb);
                struct arp_eth_header *arp;
 
                arp = (struct arp_eth_header *)skb_network_header(skb);
 
-               if (arp->ar_hrd == htons(ARPHRD_ETHER)
-                               && arp->ar_pro == htons(ETH_P_IP)
-                               && arp->ar_hln == ETH_ALEN
-                               && arp->ar_pln == 4) {
-
+               if (arp_available &&
+                   arp->ar_hrd == htons(ARPHRD_ETHER) &&
+                   arp->ar_pro == htons(ETH_P_IP) &&
+                   arp->ar_hln == ETH_ALEN &&
+                   arp->ar_pln == 4) {
                        /* We only match on the lower 8 bits of the opcode. */
                        if (ntohs(arp->ar_op) <= 0xff)
                                key->ip.proto = ntohs(arp->ar_op);