[PATCH 1/2] net: ipv4: Fix a possible null-pointer dereference in inet_csk_rebuild_route()

[PATCH 1/2] net: ipv4: Fix a possible null-pointer dereference in inet_csk_rebuild_route()

[Jia-Ju Bai]

In inet_csk_rebuild_route(), rt is assigned to NULL on line 1071.
On line 1076, rt is used:
    return &rt->dst;
Thus, a possible null-pointer dereference may occur.

To fix this bug, rt is checked before being used.

This bug is found by a static analysis tool STCheck written by us.

Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
---
 net/ipv4/inet_connection_sock.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index f5c163d4771b..27d9d80f3401 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -1073,7 +1073,10 @@ static struct dst_entry *inet_csk_rebuild_route(struct sock *sk, struct flowi *f
 		sk_setup_caps(sk, &rt->dst);
 	rcu_read_unlock();
 
-	return &rt->dst;
+	if (rt)
+		return &rt->dst;
+	else
+		return NULL;
 }
 
 struct dst_entry *inet_csk_update_pmtu(struct sock *sk, u32 mtu)
-- 
2.17.0

Re: [PATCH 1/2] net: ipv4: Fix a possible null-pointer dereference in inet_csk_rebuild_route()

[Nicolas Dichtel]

Le 26/07/2019 à 04:25, Jia-Ju Bai a écrit :
> In inet_csk_rebuild_route(), rt is assigned to NULL on line 1071.
> On line 1076, rt is used:
>     return &rt->dst;
> Thus, a possible null-pointer dereference may occur.>
> To fix this bug, rt is checked before being used.
> 
> This bug is found by a static analysis tool STCheck written by us.
> 
> Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
> ---
>  net/ipv4/inet_connection_sock.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
> index f5c163d4771b..27d9d80f3401 100644
> --- a/net/ipv4/inet_connection_sock.c
> +++ b/net/ipv4/inet_connection_sock.c
> @@ -1073,7 +1073,10 @@ static struct dst_entry *inet_csk_rebuild_route(struct sock *sk, struct flowi *f
>  		sk_setup_caps(sk, &rt->dst);
>  	rcu_read_unlock();
>  
> -	return &rt->dst;
> +	if (rt)
> +		return &rt->dst;
> +	else
> +		return NULL;
Hmm, ->dst is the first field (and that will never change), thus &rt->dst is
NULL if rt is NULL.
I don't think there is a problem with the current code.


Regards,
Nicolas

Re: [PATCH 1/2] net: ipv4: Fix a possible null-pointer dereference in inet_csk_rebuild_route()

[David Miller]

From: Jia-Ju Bai <baijiaju1990@gmail.com>
Date: Fri, 26 Jul 2019 10:25:34 +0800

> diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
> index f5c163d4771b..27d9d80f3401 100644
> --- a/net/ipv4/inet_connection_sock.c
> +++ b/net/ipv4/inet_connection_sock.c
> @@ -1073,7 +1073,10 @@ static struct dst_entry *inet_csk_rebuild_route(struct sock *sk, struct flowi *f
>  		sk_setup_caps(sk, &rt->dst);
>  	rcu_read_unlock();
>  
> -	return &rt->dst;
> +	if (rt)
> +		return &rt->dst;
> +	else
> +		return NULL;

If rt is NULL, &rt->dst is also NULL as has been pointed out to you.

Please fix your automated tools to understand this case before submitting
more changes.

Thank you.