Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Reply-To: nicolas.dichtel@6wind.com
Subject: Re: [PATCH 1/2] net: ipv4: Fix a possible null-pointer dereference in
 inet_csk_rebuild_route()
To:     Jia-Ju Bai <baijiaju1990@gmail.com>, davem@davemloft.net,
        kuznet@ms2.inr.ac.ru, yoshfuji@linux-ipv6.org
Cc:     netdev@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20190726022534.24994-1-baijiaju1990@gmail.com>
From:   Nicolas Dichtel <nicolas.dichtel@6wind.com>
Organization: 6WIND
Message-ID: <64986d3e-3ee8-896f-0261-3d9cc595ba11@6wind.com>
Date:   Fri, 26 Jul 2019 11:15:55 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101
 Thunderbird/60.8.0
MIME-Version: 1.0
In-Reply-To: <20190726022534.24994-1-baijiaju1990@gmail.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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