FFS data integrity

[Pablo Marín Ramón]

(I didn't know this mailing list and I sent this message to
freebsd-questions@ about 2 hours ago. It's more on-topic here, so
I crosspost it. Sorry for the inconveniences.)

Here goes a newbie question about classical FFS (without
softupdates).

As metadata is updated synchronously, can an i-node, at some
point, end pointing to not written yet data blocks? Is this a
security risk, i.e., can those pointed to data blocks pertain to
another user's deleted on memory but not deleted on disk data, or
that deleted data will be marked in metadata as not initialized
and after a crash fsck will fix all i-nodes pointing to it?

AFAIK, softupdates and ext3 in the default mode (data=ordered)
don't have this problem, but journalling filesystems that journal
only metadata do. Is this correct?

Thanks in advance.