Re: [PATCH 1/2] Btrfs: add more valid checks for superblock

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On Tue, May 03, 2016 at 09:02:56AM +0800, Qu Wenruo wrote:
> 
> 
> Liu Bo wrote on 2016/05/02 11:15 -0700:
> > This adds valid checks for super_total_bytes, super_bytes_used and
> > super_stripesize.
> >
> > Reported-by: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
> > Reported-by: Quentin Casasnovas <quentin.casasnovas@xxxxxxxxxx>
> > Signed-off-by: Liu Bo <bo.li.liu@xxxxxxxxxx>
> > ---
> >  fs/btrfs/disk-io.c | 14 ++++++++++++++
> >  1 file changed, 14 insertions(+)
> >
> > diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> > index 4e47849..988d03f 100644
> > --- a/fs/btrfs/disk-io.c
> > +++ b/fs/btrfs/disk-io.c
> > @@ -4120,6 +4120,20 @@ static int btrfs_check_super_valid(struct btrfs_fs_info *fs_info,
> >  	 * Hint to catch really bogus numbers, bitflips or so, more exact checks are
> >  	 * done later
> >  	 */
> > +	if (btrfs_super_total_bytes(sb) == 0) {
> > +		printk(KERN_ERR "BTRFS: total bytes is zero\n");
> > +		ret = -EINVAL;
> > +	}
> 
> Would it be better if using "6 * nodesize"?
> 
> I'd like to use a precious low limit on total bytes, but we don't have 
> such value, so 6 nodesize would be good.

An early check can compare against some reasonable value, but the
total_bytes value must be equal to the sum of all device sizes
(disk_total_bytes). I'm not sure if we have enough information to verify
that at this point though.
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