[PATCH] net: geneve: Fix a possible null-pointer dereference in geneve_link_config()

[PATCH] net: geneve: Fix a possible null-pointer dereference in geneve_link_config()

[Jia-Ju Bai]

In geneve_link_config(), there is an if statement on line 1524 to check
whether rt is NULL:
    if (rt && rt->dst.dev)

When rt is NULL, it is used on line 1526:
    ip6_rt_put(rt)
        dst_release(&rt->dst);

Thus, a possible null-pointer dereference may occur.

To fix this bug, ip6_rt_put(rt) 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>
---
 drivers/net/geneve.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/net/geneve.c b/drivers/net/geneve.c
index cb2ea8facd8d..a47a1b31b166 100644
--- a/drivers/net/geneve.c
+++ b/drivers/net/geneve.c
@@ -1521,9 +1521,10 @@ static void geneve_link_config(struct net_device *dev,
 		rt = rt6_lookup(geneve->net, &info->key.u.ipv6.dst, NULL, 0,
 				NULL, 0);
 
-		if (rt && rt->dst.dev)
+		if (rt && rt->dst.dev) {
 			ldev_mtu = rt->dst.dev->mtu - GENEVE_IPV6_HLEN;
-		ip6_rt_put(rt);
+			ip6_rt_put(rt);
+		}
 		break;
 	}
 #endif
-- 
2.17.0

Re: [PATCH] net: geneve: Fix a possible null-pointer dereference in geneve_link_config()

[Jiri Benc]

On Mon, 29 Jul 2019 18:26:11 +0800, Jia-Ju Bai wrote:
> --- a/drivers/net/geneve.c
> +++ b/drivers/net/geneve.c
> @@ -1521,9 +1521,10 @@ static void geneve_link_config(struct net_device *dev,
>  		rt = rt6_lookup(geneve->net, &info->key.u.ipv6.dst, NULL, 0,
>  				NULL, 0);
>  
> -		if (rt && rt->dst.dev)
> +		if (rt && rt->dst.dev) {
>  			ldev_mtu = rt->dst.dev->mtu - GENEVE_IPV6_HLEN;
> -		ip6_rt_put(rt);
> +			ip6_rt_put(rt);
> +		}
>  		break;
>  	}
>  #endif

Are you sure rt6_lookup can never return a non-NULL rt with rt->dst.dev
being NULL? You'd leak the reference in such case.

 Jiri

Re: [PATCH] net: geneve: Fix a possible null-pointer dereference in geneve_link_config()

[Jiri Benc]

On Mon, 29 Jul 2019 12:30:55 +0200, Jiri Benc wrote:
> Are you sure rt6_lookup can never return a non-NULL rt with rt->dst.dev
> being NULL? You'd leak the reference in such case.

In fact, you're introducing a bug, not fixing one. ip6_rt_put does
accept NULL parameter. And it seems you already have been told that?

Nacked-by: Jiri Benc <jbenc@redhat.com>

 Jiri