From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <smatch-owner@vger.kernel.org>
Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54566 "EHLO
        lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S229567AbhHCQEO (ORCPT
        <rfc822;smatch@vger.kernel.org>); Tue, 3 Aug 2021 12:04:14 -0400
Received: from mail-lf1-x131.google.com (mail-lf1-x131.google.com [IPv6:2a00:1450:4864:20::131])
        by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C8012C061757
        for <smatch@vger.kernel.org>; Tue,  3 Aug 2021 09:04:02 -0700 (PDT)
Received: by mail-lf1-x131.google.com with SMTP id h2so40614020lfu.4
        for <smatch@vger.kernel.org>; Tue, 03 Aug 2021 09:04:02 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
        d=gmail.com; s=20161025;
        h=subject:to:cc:references:from:message-id:date:user-agent
         :mime-version:in-reply-to:content-language:content-transfer-encoding;
        bh=b0sIfA8FpNIM6xTkEutBlL5Ds5MNrhPhPuFTRp6Km9o=;
        b=ud6qMISVxTlA723piY50eTeuyo+FHZn93PqfpyEEtiatlyYN9RevAajH26iJhGB23V
         WBcpw8sws05Ll8tUV8qXegCC2rb0GtL7s3UbeL5gpUnM900AtXBjbf0XnU7m5TmMc5hu
         k5G9kZI8sMHbFyVgFd5Tq5YvWd9DvnqQ3Cg0gIKtDPIbraDjmaKXIQuLfsqgc+v43NIk
         u8m0Q4fKD/TbsvFgJNKb1HiZJD7jIGlmCHfeVPFhdqAzcYg0c33S8Yk6UdAa2Dg7BIC1
         Wa1qQzFtWmRQWwf+fdncOSgJOxr7d9TLnldVbhhUfKAFjsSgrOYW5Upvcg+rcdny8q1m
         +hYQ==
Subject: Re: [PATCH] check_netdev_priv: warn about using netdev priv data
 after free_netdev
References: <20210802210022.5226-1-paskripkin@gmail.com>
 <20210803150826.GC1931@kadam>
From: Pavel Skripkin <paskripkin@gmail.com>
Message-ID: <41b1499c-3715-30df-b083-159c7d71efcb@gmail.com>
Date: Tue, 3 Aug 2021 19:03:59 +0300
MIME-Version: 1.0
In-Reply-To: <20210803150826.GC1931@kadam>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
List-ID: <smatch.vger.kernel.org>
To: Dan Carpenter <dan.carpenter@oracle.com>
Cc: smatch@vger.kernel.org

Hi, Dan!

On 8/3/21 6:08 PM, Dan Carpenter wrote:
> Thanks Pavel!
> 
> It looks really nice.  I've applied it.  I'll test it tonight and push
> tomorrow.
> 
> I don't see any major issues with the check at all, but I have a few
> comments below.
> 
> On Tue, Aug 03, 2021 at 12:00:22AM +0300, Pavel Skripkin wrote:
>> +static void match_free_netdev(const char *fn, struct expression *expr, void *_arg_no)
>> +{
>> +	struct expression *arg;
>> +	const char *name;
>> +
>> +	arg = get_argument_from_call_expr(expr->args, PTR_INT(_arg_no));
>> +	if (!arg)
>> +		return;
>> +
>> +	name = expr_to_var(arg);
>> +	if (!name)
>> +		return;
>> +
>> +	set_state(my_id, name, NULL, &freed);
>> +}
> 
> There is a new param_key API which would make this function shorter.
> 
> static void free_netdev(struct expression *expr, const char *name, struct symbol *sym, void *data)
> {
> 	set_state(my_id, name, NULL, &freed);
> }
> 
> Then in the register function you'd add a hooks like this:
> 
> 	add_function_param_key_hook("free_netdev", &free_netdev, 0, "$", NULL);
> 	add_function_param_key_hook("free_candev", &free_netdev, 0, "$", NULL);
> 

I guess, I missed that API, sorry :( Next time I will use it instead.

> Of course, you've already written your own code which works so it's
> fine.  But that param_key API is really the most awesome thing.
> 
>> +
>> +static void match_symbol(struct expression *expr)
>> +{
>> +	const char *parent_netdev, *name;
>> +	struct smatch_state *state;
>> +
> 
> This hook is run for every variable so it's tempting to add a shortcut
> here:
> 
> 	if (!has_states(my_id))
> 		return;
> 
>> +	name = expr_to_var(expr);
>> +	if (!name)
>> +		return;
>> +
>> +	parent_netdev = get_parent_netdev_name(expr);
>> +	if (!parent_netdev)
>> +		return;
>> +	
>> +	state = get_state(my_id, parent_netdev, NULL);
>> +	if (state == &freed)
>> +		sm_error("Using %s after free_{netdev,candev}(%s);\n", name, parent_netdev);
>> +}
>> +
>> +void check_uaf_netdev_priv(int id)
>> +{
>> +	if (option_project != PROJ_KERNEL)
>> +		return;
>> +
>> +	my_id = id;
>> +
>> +	add_function_hook("free_netdev", &match_free_netdev, NULL);
> 
> NULL works but INT_PTR(0) is nicer.  ;)
> 
>> +	add_function_hook("free_candev", &match_free_netdev, NULL);
>> +	add_modification_hook(my_id, &ok_to_use);
>> +	add_hook(&match_symbol, SYM_HOOK);
>> +}
> 
> Anyway, I think I will probably add the has_states() check but the
> rest isn't important.


Thank you for applying and your guidelines, I appreciate it :)



With regards,
Pavel Skripkin