linux-kernel - Re: [PATCH] net: tipc: Fix a possible null-pointer dereference in tipc_publ

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Message-ID: <31091d78-8c10-f07d-b738-4c082d33f1c9@windriver.com>
Date:   Fri, 26 Jul 2019 22:10:17 +0800
From:   Ying Xue <ying.xue@...driver.com>
To:     Jia-Ju Bai <baijiaju1990@...il.com>, <jon.maloy@...csson.com>,
        <davem@...emloft.net>
CC:     <netdev@...r.kernel.org>, <tipc-discussion@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: tipc: Fix a possible null-pointer dereference in
 tipc_publ_purge()

On 7/25/19 5:20 PM, Jia-Ju Bai wrote:
> In tipc_publ_purge(), there is an if statement on 215 to 
> check whether p is NULL: 
>     if (p)
> 
> When p is NULL, it is used on line 226:
>     kfree_rcu(p, rcu);
> 
> Thus, a possible null-pointer dereference may occur.
> 
> To fix this bug, p 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/tipc/name_distr.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/net/tipc/name_distr.c b/net/tipc/name_distr.c
> index 44abc8e9c990..241ed2274473 100644
> --- a/net/tipc/name_distr.c
> +++ b/net/tipc/name_distr.c
> @@ -223,7 +223,8 @@ static void tipc_publ_purge(struct net *net, struct publication *publ, u32 addr)
>  		       publ->key);
>  	}
>  
> -	kfree_rcu(p, rcu);
> +	if (p)

No, I don't think so because kfree_rcu() will internally check if "p"
pointer is NULL or not.

> +		kfree_rcu(p, rcu);
>  }
>  
>  /**
>