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

[Zhihao Cheng]

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@xxxxxxxxxxxxxxx
>
> 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