On Fri, Dec 04, 2015 at 05:43:49PM -0600, Serge E. Hallyn wrote:

On Fri, Dec 04, 2015 at 06:11:52PM -0500, Theodore Ts'o wrote:

quoted

On Fri, Dec 04, 2015 at 02:45:32PM -0600, Seth Forshee wrote:

quoted

On Fri, Dec 04, 2015 at 02:07:36PM -0600, Serge E. Hallyn wrote:

quoted

Heh, I was looking over http://www.gossamer-threads.com/lists/linux/kernel/103611
a little while ago :)  The same question was asked 16 years ago.  Apparently
the answer then was that it was easier than fixing the code.

So it seems then that either it still isn't safe and so unprivileged
users shouldn't be allowed to do it at all, or else it's safe and we
should drop the requirement completely. I can't say which is right,
unfortunately.

It may not have been safe 16 years agoo, but giving invalid arguments
to FIBMAP is safe for ext4 and ext2.  This is the sort of thing that
tools like trinity should and does test for, so I think it should be
fine to remove the root check for FIBMAP.

Seth, can I tempt you into sending a standalone patch to remove that? :)

Patch sent. I'll drop this patch in v2.