linux-kernel - Re: [PATCH v2] staging: erofs: keep corrupted fs from crashing kernel in erofs

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Message-ID: <71f44997-a32a-1384-e350-dc822a2cea13@huawei.com>
Date:   Fri, 15 Feb 2019 17:04:02 +0800
From:   Gao Xiang <gaoxiang25@...wei.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
CC:     Chao Yu <yuchao0@...wei.com>, Al Viro <viro@...IV.linux.org.uk>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        <devel@...verdev.osuosl.org>, <linux-erofs@...ts.ozlabs.org>,
        Chao Yu <chao@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
        <stable@...r.kernel.org>, <weidu.du@...wei.com>,
        Fang Wei <fangwei1@...wei.com>, Miao Xie <miaoxie@...wei.com>
Subject: Re: [PATCH v2] staging: erofs: keep corrupted fs from crashing kernel
 in erofs_namei()

Hi Dan,

On 2019/2/15 15:57, Dan Carpenter wrote:
> On Fri, Feb 15, 2019 at 03:02:25PM +0800, Chao Yu wrote:
>> On 2019/2/1 20:16, Gao Xiang wrote:
>>> +	/*
>>> +	 * on-disk error, let's only BUG_ON in the debugging mode.
>>> +	 * otherwise, it will return 1 to just skip the invalid name
>>> +	 * and go on (in consideration of the lookup performance).
>>> +	 */
>>> +	DBG_BUGON(qd->name > qd->end);
>>
>> qd->name == qd->end is not allowed as well?
>>
>> So will it be better to return directly here?
>>
>> 	if (unlikely(qd->name >= qd->end)) {
>> 		DBG_BUGON(1);
>> 		return 1;
>> 	}
> 
> Please don't add likely/unlikely() annotations unless you have
> benchmarked it and it makes a difference.

I tend not to add this branch above since the current logic can handle
qd->name >= qd->end (it only happens in corrupted images) and
it will return 1;

Let's just leave DBG_BUGON(qd->name > qd->end); here for debugging use
(to detect corrupted image in some degree earlier).

Thanks,
Gao Xiang

> 
> regards,
> dan carpenter
> 
>