linux-kernel - Re: [PATCH 1/2] net: ipv4: Fix a possible null-pointer dereference in inet_csk_rebuild

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Date:   Fri, 26 Jul 2019 11:15:55 +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 1/2] net: ipv4: Fix a possible null-pointer dereference in
 inet_csk_rebuild_route()

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@...il.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