Re: [PATCH 1/3] ext4: super: Fix spectre gadget in ext4_quota_on

[Josh Poimboeuf]

On Tue, Jul 31, 2018 at 12:39:41AM -0600, Andreas Dilger wrote:
> > Also it looks like XQM_MAXQUOTAS, MAXQUOTAS, and EXT4_MAXQUOTAS all
> > have the same value (3).  Maybe they can be consolidated to just use
> > MAXQUOTAS everywhere?
> 
> No, the filesystem-specific MAXQUOTAS values were separated from
> the kernel MAXQUOTAS value for a good reason.  This allows some
> filesystems to support new quota types (e.g. project quotas) that
> not all other filesystems can handle.  This may potentially change
> again in the future, so they shouldn't be tightly coupled.

But isn't that what sb->s_quota_types is for?  To allow different
filesystems to support different quota types?

Also I don't see any bounds checks for EXT4_MAXQUOTAS.  It seems like
the ext4 code assumes that MAXQUOTAS and EXT4_MAXQUOTAS are the same.

-- 
Josh