Re: [PATCH v1] security: Add a new hook: inode_touch_atime

[Al Viro]

On Thu, Dec 22, 2016 at 01:01:39AM +0100, Mickaël Salaün wrote:

> SELinux should be interested. This is useful to create sandboxes so
> other LSM may be interested too
> 
> I'm working on a new LSM and I would like this kind of hook to create a
> real read-only environment.

What the...?  Have you noticed
        if (!sb_start_write_trylock(inode->i_sb))
                return;

        if (__mnt_want_write(mnt) != 0)
                goto skip_update;
in touch_atime()?  Just mount them read-only in your sandbox (on either
level - both per-mountpoint and per-fs r/o will do) and be done
with that; why bother with LSM when regular tools would suffice?