[PATCH][netdev-next] gre: remove duplicated assignment of iph

[PATCH][netdev-next] gre: remove duplicated assignment of iph

[Colin King]

From: Colin Ian King <colin.king@canonical.com>

iph is being assigned the same value twice; remove the redundant
second assignment.

Fixes warning:
net/ipv4/ip_gre.c:265:2: warning: Value stored to 'iph' is never read

Signed-off-by: Colin Ian King <colin.king@canonical.com>
---
 net/ipv4/ip_gre.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
index 6e8a62289e03..6b3e7c99a3b6 100644
--- a/net/ipv4/ip_gre.c
+++ b/net/ipv4/ip_gre.c
@@ -268,7 +268,6 @@ static int erspan_rcv(struct sk_buff *skb, struct tnl_ptk_info *tpi,
 	if (unlikely(!pskb_may_pull(skb, len)))
 		return -ENOMEM;
 
-	iph = ip_hdr(skb);
 	ershdr = (struct erspanhdr *)(skb->data + gre_hdr_len);
 
 	/* The original GRE header does not have key field,
-- 
2.14.1

Re: [PATCH][netdev-next] gre: remove duplicated assignment of iph

[Nikolay Aleksandrov]

On 23/08/17 14:13, Colin King wrote:
> From: Colin Ian King <colin.king@canonical.com>
> 
> iph is being assigned the same value twice; remove the redundant
> second assignment.
> 
> Fixes warning:
> net/ipv4/ip_gre.c:265:2: warning: Value stored to 'iph' is never read
> 
> Signed-off-by: Colin Ian King <colin.king@canonical.com>
> ---
>  net/ipv4/ip_gre.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c
> index 6e8a62289e03..6b3e7c99a3b6 100644
> --- a/net/ipv4/ip_gre.c
> +++ b/net/ipv4/ip_gre.c
> @@ -268,7 +268,6 @@ static int erspan_rcv(struct sk_buff *skb, struct tnl_ptk_info *tpi,
>  	if (unlikely(!pskb_may_pull(skb, len)))
>  		return -ENOMEM;
>  
> -	iph = ip_hdr(skb);
>  	ershdr = (struct erspanhdr *)(skb->data + gre_hdr_len);
>  
>  	/* The original GRE header does not have key field,
> 

This one looks like a correct assignment, I'd remove the previous one because
pskb_may_pull may change the header pointers and the previously assigned iph might
become wrong.

Also add the author of the code to the CC list.

Re: [PATCH][netdev-next] gre: remove duplicated assignment of iph

[David Miller]

From: Colin King <colin.king@canonical.com>
Date: Wed, 23 Aug 2017 12:13:05 +0100

> From: Colin Ian King <colin.king@canonical.com>
> 
> iph is being assigned the same value twice; remove the redundant
> second assignment.
> 
> Fixes warning:
> net/ipv4/ip_gre.c:265:2: warning: Value stored to 'iph' is never read
> 
> Signed-off-by: Colin Ian King <colin.king@canonical.com>

It is always necessary to reload any SKB header pointer after calls
to functions which potentially change the data buffer of the SKB.

pskb_may_pull() is one such call.

Therefore your patch is adding a bug.

If you want to remove the dup, you must remove the first not
the second one.