linux-kernel - Re: [PATCH] ipv6:ipv6_pinfo dereferenced after NULL check

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Date:   Tue, 22 Nov 2016 13:26:45 +0100
From:   Hannes Frederic Sowa <hannes@...essinduktion.org>
To:     Manjeet Pawar <manjeet.p@...sung.com>, davem@...emloft.net,
        kuznet@....inr.ac.ru, jmorris@...ei.org, yoshfuji@...ux-ipv6.org,
        kaber@...sh.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     pankaj.m@...sung.com, ajeet.y@...sung.com,
        Rohit Thapliyal <r.thapliyal@...sung.com>
Subject: Re: [PATCH] ipv6:ipv6_pinfo dereferenced after NULL check

On 22.11.2016 07:27, Manjeet Pawar wrote:
> From: Rohit Thapliyal <r.thapliyal@...sung.com>
> 
> np checked for NULL and then dereferenced. It should be modified
> for NULL case.
> 
> Signed-off-by: Rohit Thapliyal <r.thapliyal@...sung.com>
> Signed-off-by: Manjeet Pawar <manjeet.p@...sung.com>
> ---
>  net/ipv6/ip6_output.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
> index 1dfc402..c2afa14 100644
> --- a/net/ipv6/ip6_output.c
> +++ b/net/ipv6/ip6_output.c
> @@ -205,14 +205,15 @@ int ip6_xmit(const struct sock *sk, struct sk_buff *skb, struct flowi6 *fl6,
>  	/*
>  	 *	Fill in the IPv6 header
>  	 */
> -	if (np)
> +	if (np) {
>  		hlimit = np->hop_limit;
> +		ip6_flow_hdr(
> +					hdr, tclass, ip6_make_flowlabel(
> +					net, skb, fl6->flowlabel,
> +					np->autoflowlabel, fl6));
> +	}
>  	if (hlimit < 0)
>  		hlimit = ip6_dst_hoplimit(dst);
>  
> -	ip6_flow_hdr(hdr, tclass, ip6_make_flowlabel(net, skb, fl6->flowlabel,
> -				np->autoflowlabel, fl6));
> -
>  	hdr->payload_len = htons(seg_len);
>  	hdr->nexthdr = proto;
>  	hdr->hop_limit = hlimit;
> 


We always should initialize hdr and not skip the ip6_flow_hdr call.

Do you saw a bug or did you find this by code review? I wonder if np can
actually be NULL at this point. Maybe we can just eliminate the NULL check.

Thanks,
Hannes