netdev - Re: [PATCH 2/2] net: ipv6: Fix a possible null-pointer dereference in vti6_link

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Date:   Fri, 26 Jul 2019 11:21:18 +0200
From:   Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:     Jia-Ju Bai <baijiaju1990@...il.com>, davem@...emloft.net,
        kuznet@....inr.ac.ru, yoshfuji@...ux-ipv6.org
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] net: ipv6: Fix a possible null-pointer dereference in
 vti6_link_config()

Le 26/07/2019 à 10:03, Jia-Ju Bai a écrit :
> In vti6_link_config(), there is an if statement on line 649 to check
> whether rt is NULL:
>     if (rt)
> 
> When rt is NULL, it is used on line 651:
>     ip6_rt_put(rt);
>         dst_release(&rt->dst);
> 
> Thus, a possible null-pointer dereference may occur.
> 
> To fix this bug, ip6_rt_put() is called when rt is not NULL.
> 
> This bug is found by a static analysis tool STCheck written by us.
> 
> Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
> ---
>  net/ipv6/ip6_vti.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/net/ipv6/ip6_vti.c b/net/ipv6/ip6_vti.c
> index 024db17386d2..572647205c52 100644
> --- a/net/ipv6/ip6_vti.c
> +++ b/net/ipv6/ip6_vti.c
> @@ -646,9 +646,10 @@ static void vti6_link_config(struct ip6_tnl *t, bool keep_mtu)
>  						 &p->raddr, &p->laddr,
>  						 p->link, NULL, strict);
>  
> -		if (rt)
> +		if (rt) {
>  			tdev = rt->dst.dev;
> -		ip6_rt_put(rt);
> +			ip6_rt_put(rt);
> +		}
Please, look at ip6_rt_put(), it is explicitly stated that it can be called with
rt == NULL.