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    SubjectRe: [PATCH 1/3] quota: Check next/prev free block number after reading from quota file
    On Thu 22-09-22 16:13:59, Zhihao Cheng wrote:
    > 在 2022/9/21 21:37, Jan Kara 写道:
    > > > --- 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.

    Good point! 0 means "not present". So any block number (either in free list
    or pointed from the quota tree) should be either 0 or > QT_TREEOFF.

    Honza
    --
    Jan Kara <jack@suse.com>
    SUSE Labs, CR

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