flow dissector: check if arp_eth is null rather than arp

arp is being checked instead of arp_eth to see if the call to
__skb_header_pointer failed. Fix this by checking arp_eth is
null instead of arp.   Also fix to use length hlen rather than
hlen - sizeof(_arp); thanks to Eric Dumazet for spotting
this latter issue.

CoverityScan CID#1396428 ("Logically dead code") on 2nd
arp comparison (which should be arp_eth instead).

Fixes: commit 55733350e5e8b70c5 ("flow disector: ARP support")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index e3dffc7..c35aae1 100644 (file)
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -407,9 +407,9 @@ mpls:
 
                arp_eth = __skb_header_pointer(skb, nhoff + sizeof(_arp),
                                               sizeof(_arp_eth), data,
-                                              hlen - sizeof(_arp),
+                                              hlen,
                                               &_arp_eth);
-               if (!arp)
+               if (!arp_eth)
                        goto out_bad;
 
                if (dissector_uses_key(flow_dissector,