[PATCH net] rps: flow_dissector: Fix uninitialized flow_keys used in __skb_get_hash possibly

From: Gao Feng <redacted>

The original codes depend on that the function parameters are evaluated from
left to right. But the parameter's evaluation order is not defined in C
standard actually.

When flow_keys_have_l4(&keys) is invoked before ___skb_get_hash(skb, &keys,
hashrnd) with some compilers or environment, the keys passed to
flow_keys_have_l4 is not initialized.

Signed-off-by: Gao Feng <redacted>
---
 net/core/flow_dissector.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index 61ad43f..52742a0 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c

@@ -680,11 +680,13 @@ EXPORT_SYMBOL_GPL(__skb_get_hash_symmetric);
 void __skb_get_hash(struct sk_buff *skb)
 {
 	struct flow_keys keys;
+	u32 hash;
 
 	__flow_hash_secret_init();
 
-	__skb_set_sw_hash(skb, ___skb_get_hash(skb, &keys, hashrnd),
-			  flow_keys_have_l4(&keys));
+	hash = ___skb_get_hash(skb, &keys, hashrnd);
+
+	__skb_set_sw_hash(skb, hash, flow_keys_have_l4(&keys));
 }
 EXPORT_SYMBOL(__skb_get_hash);
 

-- 
1.9.1

On Wed, 2016-08-31 at 10:56 +0800, fgao@ikuai8.com wrote:

From: Gao Feng <redacted>

The original codes depend on that the function parameters are evaluated from
left to right. But the parameter's evaluation order is not defined in C
standard actually.

When flow_keys_have_l4(&keys) is invoked before ___skb_get_hash(skb, &keys,
hashrnd) with some compilers or environment, the keys passed to
flow_keys_have_l4 is not initialized.

Signed-off-by: Gao Feng <redacted>
---

Good catch, please add 

Fixes: 6db61d79c1e1 ("flow_dissector: Ignore flow dissector return value from ___skb_get_hash")
Acked-by: Eric Dumazet <edumazet@google.com>

On Wed, Aug 31, 2016 at 12:14 PM, Eric Dumazet [off-list ref] wrote:

On Wed, 2016-08-31 at 10:56 +0800, fgao@ikuai8.com wrote:

quoted

From: Gao Feng <redacted>

The original codes depend on that the function parameters are evaluated from
left to right. But the parameter's evaluation order is not defined in C
standard actually.

When flow_keys_have_l4(&keys) is invoked before ___skb_get_hash(skb, &keys,
hashrnd) with some compilers or environment, the keys passed to
flow_keys_have_l4 is not initialized.

Signed-off-by: Gao Feng <redacted>
---

Good catch, please add

Fixes: 6db61d79c1e1 ("flow_dissector: Ignore flow dissector return value from ___skb_get_hash")
Acked-by: Eric Dumazet <edumazet@google.com>

Add it into the description and resend the patch again?

Best Regards
Feng

On Wed, Aug 31, 2016 at 12:16 PM, Gao Feng [off-list ref] wrote:

On Wed, Aug 31, 2016 at 12:14 PM, Eric Dumazet [off-list ref] wrote:

quoted

On Wed, 2016-08-31 at 10:56 +0800, fgao@ikuai8.com wrote:

quoted

From: Gao Feng <redacted>

The original codes depend on that the function parameters are evaluated from
left to right. But the parameter's evaluation order is not defined in C
standard actually.

When flow_keys_have_l4(&keys) is invoked before ___skb_get_hash(skb, &keys,
hashrnd) with some compilers or environment, the keys passed to
flow_keys_have_l4 is not initialized.

Signed-off-by: Gao Feng <redacted>
---

Good catch, please add

Fixes: 6db61d79c1e1 ("flow_dissector: Ignore flow dissector return value from ___skb_get_hash")
Acked-by: Eric Dumazet <edumazet@google.com>

Add it into the description and resend the patch again?

Best Regards
Feng

Hi Eric,

I have sent the update "v2" patch which has the description "Fixes:
6db61d79c1e1 ("flow_dissector: Ignore flow dissector return value from
___skb_get_hash")".
Could you help review it again please?

Best Regards
Feng