[PATCH 2/2] net: ipv6: Fix a possible null-pointer dereference in vti6_link_config()

[PATCH 2/2] net: ipv6: Fix a possible null-pointer dereference in vti6_link_config()

[Jia-Ju Bai]

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@gmail.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);
+		}
 	}
 
 	if (!tdev && p->link)
-- 
2.17.0

Re: [PATCH 2/2] net: ipv6: Fix a possible null-pointer dereference in vti6_link_config()

[Nicolas Dichtel]

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@gmail.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.

Re: [PATCH 2/2] net: ipv6: Fix a possible null-pointer dereference in vti6_link_config()

[David Miller]

From: Jia-Ju Bai <baijiaju1990@gmail.com>
Date: Fri, 26 Jul 2019 16:03:21 +0800

> @@ -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);
> +		}

ip6_rt_put() can take a NULL argument without any problem.

I want to make it clear that because of mistakes of this nature, and
how frequently you make them, it is very tiring and exhausting to
review your changes...