From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1751705AbdCRR2A (ORCPT <rfc822;w@1wt.eu>);
        Sat, 18 Mar 2017 13:28:00 -0400
Received: from mail-lf0-f48.google.com ([209.85.215.48]:34958 "EHLO
        mail-lf0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1751127AbdCRR16 (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Sat, 18 Mar 2017 13:27:58 -0400
Subject: Re: [PATCH] net: convert sk_filter.refcnt from atomic_t to refcount_t
To: Elena Reshetova <elena.reshetova@intel.com>, daniel@iogearbox.net
References: <1489841889-27601-1-git-send-email-elena.reshetova@intel.com>
Cc: ast@fb.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        peterz@infradead.org, keescook@chromium.org,
        Hans Liljestrand <ishkamiel@gmail.com>,
        David Windsor <dwindsor@gmail.com>
From: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Message-ID: <a19263a2-141b-22ad-4300-0ffe54cae8d6@cogentembedded.com>
Date: Sat, 18 Mar 2017 17:33:22 +0300
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101
 Thunderbird/45.8.0
MIME-Version: 1.0
In-Reply-To: <1489841889-27601-1-git-send-email-elena.reshetova@intel.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

Hello!

On 3/18/2017 3:58 PM, Elena Reshetova wrote:

> refcount_t type and corresponding API should be
> used instead of atomic_t when the variable is used as
> a reference counter. This allows to avoid accidental
> refcounter overflows that might lead to use-after-free
> situations.
>
> Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
> Signed-off-by: Hans Liljestrand <ishkamiel@gmail.com>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> Signed-off-by: David Windsor <dwindsor@gmail.com>
[...]
> diff --git a/net/core/filter.c b/net/core/filter.c
> index ebaeaf2..62267e2 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
[...]
> @@ -1179,12 +1179,13 @@ static int __sk_attach_prog(struct bpf_prog *prog, struct sock *sk)
>  		return -ENOMEM;
>
>  	fp->prog = prog;
> -	atomic_set(&fp->refcnt, 0);
> +	refcount_set(&fp->refcnt, 1);
>
>  	if (!sk_filter_charge(sk, fp)) {
>  		kfree(fp);
>  		return -ENOMEM;
>  	}
> +	refcount_set(&fp->refcnt, 1);

    Why do it twice?

[...]

MBR, Sergei