Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:18 as permitted sender) client-ip=2620:137:e000::1:18;
Subject: Re: [PATCH -next] fs: sysv: check sbi->s_firstdatazone in
 complete_read_super
To:     Christoph Hellwig <hch@infradead.org>
References: <20220330104215.530223-1-liushixin2@huawei.com>
 <YkR6WdjLJyF0PMcd@infradead.org>
CC:     <linux-kernel@vger.kernel.org>
From:   Liu Shixin <liushixin2@huawei.com>
Message-ID: <a8d491c5-5af5-a9ee-441e-27fdf233eb93@huawei.com>
Date:   Thu, 31 Mar 2022 11:49:08 +0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101
 Thunderbird/45.7.1
MIME-Version: 1.0
In-Reply-To: <YkR6WdjLJyF0PMcd@infradead.org>
Content-Type: text/plain; charset="windows-1252"
Content-Transfer-Encoding: 7bit
Precedence: bulk


The type I used is sysv v7.

I discovered this problem through a syzkaller use case. The use case first create a file
via memfd and bind it to loop0. Then mount it to a folder with type v7. No error is
reported for preceding operations. Finally when create a file, the warning in inc_nlink
is triggered. I want to look the filesystem information, so I execute 'df' command and
find this problem.

Btw, I think the warning may be a follow-up problem caused by the filesystem being
created or mounted incorrectly.

Thanks,

On 2022/3/30 23:42, Christoph Hellwig wrote:
> On Wed, Mar 30, 2022 at 06:42:15PM +0800, Liu Shixin wrote:
>> sbi->s_firstinodezone is initialized to 2 and sbi->s_firstdatazone is read
>> from sbd. There's no guarantee that sbi->s_firstdatazone must bigger than
>> sbi->s_firstinodezone. If sbi->s_firstdatazone less than 2, the filesystem
>> can still be mounted unexpetly. At this point, sbi->s_ninodes flip to very
>> large value and this filesystem is broken. We can observe this by
>> executing 'df' command. When we execute, we will get an error message:
>> 	"sysv_count_free_inodes: unable to read inode table"
> This looks fine.  Just curious: which variant of the sysv fs do you
> use and what is the use case?
> .
>