Re: [PATCH] flow disector: check if arp_eth is null rather than arp

On 13/01/17 18:24, Eric Dumazet wrote:

On Fri, 2017-01-13 at 13:34 +0000, Colin King wrote:

quoted

From: Colin Ian King <redacted>

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.

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 <redacted>
---
 net/core/flow_dissector.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index e3dffc7..fec48e9 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c

@@ -409,7 +409,7 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
 					       sizeof(_arp_eth), data,
 					       hlen - sizeof(_arp),
 					       &_arp_eth);
-		if (!arp)
+		if (!arp_eth)
 			goto out_bad;
 
 		if (dissector_uses_key(flow_dissector,

It looks that we try very hard to add critical bugs in flow dissector.

This is embarrassing really.

I am questioning if the __skb_header_pointer() is correct

Why using hlen - sizeof(_arp) ?

               arp_eth = __skb_header_pointer(skb, nhoff + sizeof(_arp),
                                              sizeof(_arp_eth), data,
                                              hlen - sizeof(_arp),
                                              &_arp_eth);

Yep, the sizeof maybe dubious too, I overlooked that one; if somebody
can clarify that then I'll send a V2 if it needs fixing up too.

Colin