netdev - [PATCH net-next] flow_dissector: Fix function argument ordering dependency

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Message-ID: <1441156264-38469-1-git-send-email-tom@herbertland.com>
Date:	Tue, 1 Sep 2015 18:11:04 -0700
From:	Tom Herbert <tom@...bertland.com>
To:	<davem@...emloft.net>, <netdev@...r.kernel.org>
CC:	<kernel-team@...com>
Subject: [PATCH net-next] flow_dissector: Fix function argument ordering dependency

Commit c6cc1ca7f4d70c ("flowi: Abstract out functions to get flow hash
based on flowi") introduced a bug in __skb_set_sw_hash where we
require a dependency on evaluating arguments in a function in order.
There is no such ordering enforced in C, so this incorrect. This
patch fixes that by splitting out the arguments. This bug was
found via a compiler warning that keys may be uninitialized.

Signed-off-by: Tom Herbert <tom@...bertland.com>
---
 include/linux/skbuff.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 9e62687..eabfb81 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1035,9 +1035,9 @@ static inline __u32 skb_get_hash_flowi6(struct sk_buff *skb, struct flowi6 *fl6)
 {
 	if (!skb->l4_hash && !skb->sw_hash) {
 		struct flow_keys keys;
+		__u32 hash = __get_hash_from_flowi6(fl6, &keys);
 
-		__skb_set_sw_hash(skb, __get_hash_from_flowi6(fl6, &keys),
-				  flow_keys_have_l4(&keys));
+		__skb_set_sw_hash(skb, hash, flow_keys_have_l4(&keys));
 	}
 
 	return skb->hash;
@@ -1049,9 +1049,9 @@ static inline __u32 skb_get_hash_flowi4(struct sk_buff *skb, struct flowi4 *fl4)
 {
 	if (!skb->l4_hash && !skb->sw_hash) {
 		struct flow_keys keys;
+		__u32 hash = __get_hash_from_flowi4(fl4, &keys);
 
-		__skb_set_sw_hash(skb, __get_hash_from_flowi4(fl4, &keys),
-				  flow_keys_have_l4(&keys));
+		__skb_set_sw_hash(skb, hash, flow_keys_have_l4(&keys));
 	}
 
 	return skb->hash;
-- 
1.8.1

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