ext4: make sure bitmaps and the inode table don't overlap with bg descriptors

ext4: make sure bitmaps and the inode table don't overlap with bg descriptors

commit 77260807d1170a8cf35dbb06e07461a655f67eee upstream.

It's really bad when the allocation bitmaps and the inode table
overlap with the block group descriptors, since it causes random
corruption of the bg descriptors.  So we really want to head those off
at the pass.

https://bugzilla.kernel.org/show_bug.cgi?id=199865

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit ac93c718365ac6ea9d7631641c8dec867d623491)

Orabug: 29428607
CVE: CVE-2018-10878

Signed-off-by: John Donnelly <John.P.Donnelly@oracle.com>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>