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

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Message-ID: <56f03bdf-1817-6b3e-44d5-922637ac39f4@huawei.com>
Date:   Mon, 18 Feb 2019 10:17:28 +0800
From:   Gao Xiang <gaoxiang25@...wei.com>
To:     Chao Yu <yuchao0@...wei.com>
CC:     Al Viro <viro@...IV.linux.org.uk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        <devel@...verdev.osuosl.org>, LKML <linux-kernel@...r.kernel.org>,
        <linux-erofs@...ts.ozlabs.org>, Chao Yu <chao@...nel.org>,
        Miao Xie <miaoxie@...wei.com>, <weidu.du@...wei.com>,
        "Fang Wei" <fangwei1@...wei.com>, <stable@...r.kernel.org>
Subject: Re: [PATCH v2] staging: erofs: keep corrupted fs from crashing kernel
 in erofs_namei()

Hi Chao,

On 2019/2/18 9:39, Chao Yu wrote:
> If the image is corrupted, qn->name[i] may be anything, as you commented
> above DBG_BUGON(), we really don't need to go through any later codes, it
> can avoid potentially encoutnering wrong condition.
> 
> * otherwise, it will return 1 to just skip the invalid name
> 

Just I commented in the following source code, qn is actually the user requested
name allocated in __d_alloc, which can be guaranteed with the trailing '\0' and
it is a valid string.

Thanks,
Gao Xiang

>>>> +
>>>> +	/* qd could not have trailing '\0' */
>>>> +	/* However it is absolutely safe if < qd->end */
>>>> +	while (qd->name + i < qd->end && qd->name[i] != '\0') {
>>>> +		if (qn->name[i] != qd->name[i]) {
>>>> +			*matched = i;
>>>> +			return qn->name[i] > qd->name[i] ? 1 : -1;
>>>>  		}
>>>> -		return (qn->len > qd->len);
>>>> +		++i;
>>>>  	}
>>>> -
>>>> -	if (qn->name[i] != qd->name[i]) {
>>>> -		*matched = i;
>>>> -		return qn->name[i] > qd->name[i] ? 1 : -1;
>>>> -	}
>>>> -
>>>> -	++i;
>>>> -	goto loop;
>>>> +	*matched = i;
>>>> +	/* See comments in __d_alloc on the terminating NUL character */
>>>> +	return qn->name[i] == '\0' ? 0 : 1;
>>>>  }