Re: [patch 07/10] unprivileged mounts: add sysctl tunable for "safe" property

["Serge E. Hallyn" <serue@us.ibm.com>]

Quoting Miklos Szeredi (miklos@szeredi.hu):
> > What do you think about doing this only if FS_SAFE is also set,
> > so for instance at first only FUSE would allow itself to be
> > made user-mountable?
> > 
> > A safe thing to do, or overly intrusive?
> 
> It goes somewhat against the "no policy in kernel" policy ;).  I think
> the warning in the documentation should be enough to make sysadmins
> think twice before doing anything foolish:

Warning in which documentation?  A sysadmin considering setting fs_safe
for ext2 or xfs isn't going to be looking at fuse docs, which I think is
what you're talking about.  Are you going to add a file under
Documentation/filesystems?

> > +Care should be taken when enabling this, since most
> > +filesystems haven't been designed with unprivileged mounting
> > +in mind.
> > +
> 
> BTW, filesystems like 'proc' and 'sysfs' should also be safe, although
> the only use for them being marked safe is if the users are allowed to
> umount them from their private namespace (otherwise a 'mount --bind'
> has the same effect as a new mount).
> 
> Thanks,
> Miklos