linux-kernel - Re: [PATCH 1/3] quota: Check next/prev free block number after reading from quota file

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Date:   Thu, 22 Sep 2022 16:13:59 +0800
From:   Zhihao Cheng <chengzhihao1@...wei.com>
To:     Jan Kara <jack@...e.cz>
CC:     <jack@...e.com>, <tytso@....edu>, <brauner@...nel.org>,
        <linux-fsdevel@...r.kernel.org>, <linux-ext4@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <yukuai3@...wei.com>
Subject: Re: [PATCH 1/3] quota: Check next/prev free block number after
 reading from quota file

在 2022/9/21 21:37, Jan Kara 写道:
Hi Jan,
> On Sat 20-08-22 19:05:12, Zhihao Cheng wrote:
>> Following process:
[...]
>>
>> Link: https://bugzilla.kernel.org/show_bug.cgi?id=216372
>> Fixes: 1da177e4c3f4152 ("Linux-2.6.12-rc2")
> 
> It's better to just have:
> 
> CC: stable@...r.kernel.org
> 
> here. Fixes tag pointing to kernel release is not very useful.
Will add in v2.
> 
>> --- a/fs/quota/quota_tree.c
>> +++ b/fs/quota/quota_tree.c
>> @@ -71,6 +71,35 @@ static ssize_t write_blk(struct qtree_mem_dqinfo *info, uint blk, char *buf)
>>   	return ret;
>>   }
>>   
>> +static inline int do_check_range(struct super_block *sb, uint val, uint max_val)
>> +{
>> +	if (val >= max_val) {
>> +		quota_error(sb, "Getting block too big (%u >= %u)",
>> +			    val, max_val);
>> +		return -EUCLEAN;
>> +	}
>> +
>> +	return 0;
>> +}
> 
> I'd already provide min_val and the string for the message here as well (as
> you do in patch 2). It is less churn in the next patch and free blocks
> checking actually needs that as well. See below.
> 
>> +
>> +static int check_free_block(struct qtree_mem_dqinfo *info,
>> +			    struct qt_disk_dqdbheader *dh)
>> +{
>> +	int err = 0;
>> +	uint nextblk, prevblk;
>> +
>> +	nextblk = le32_to_cpu(dh->dqdh_next_free);
>> +	err = do_check_range(info->dqi_sb, nextblk, info->dqi_blocks);
>> +	if (err)
>> +		return err;
>> +	prevblk = le32_to_cpu(dh->dqdh_prev_free);
>> +	err = do_check_range(info->dqi_sb, prevblk, info->dqi_blocks);
>> +	if (err)
>> +		return err;
> 
> The free block should actually be > QT_TREEOFF so I'd add the check to
> do_check_range().

'dh->dqdh_next_free' may be updated when quota entry removed, 
'dh->dqdh_next_free' can be used for next new quota entris.
Before sending v2, I found 'dh->dqdh_next_free' and 'dh->dqdh_prev_free' 
can easily be zero in newly allocated blocks when continually creating 
files onwed by different users:
find_free_dqentry
   get_free_dqblk
     write_blk(info, info->dqi_blocks, buf)  // zero'd qt_disk_dqdbheader
     blk = info->dqi_blocks++   // allocate new one block
   info->dqi_free_entry = blk   // will be used for new quota entries

find_free_dqentry
   if (info->dqi_free_entry)
     blk = info->dqi_free_entry
     read_blk(info, blk, buf)   // dh->dqdh_next_free = 
dh->dqdh_prev_free = 0

I think it's normal when 'dh->dqdh_next_free' or 'dh->dqdh_prev_free' 
equals to 0.
> 
> Also rather than having check_free_block(), I'd provide a helper function
> like check_dquot_block_header() which will check only free blocks pointers
> now and in later patches you can add other checks there.
OK, will be updated in v2.
> 
> 								Honza
>