On Wed, Oct 15, 2014 at 04:07:34PM -0700, Andy Lutomirski wrote: > On Wed, Oct 15, 2014 at 3:59 PM, Seth Forshee > <seth.forshee@xxxxxxxxxxxxx> wrote: > > On Wed, Oct 15, 2014 at 10:05:46AM -0700, Andy Lutomirski wrote: > >> On Wed, Oct 15, 2014 at 8:05 AM, Seth Forshee > >> <seth.forshee@xxxxxxxxxxxxx> wrote: > >> > On Wed, Oct 15, 2014 at 07:49:39AM -0700, Andy Lutomirski wrote: > >> >> On 10/14/2014 07:25 AM, Seth Forshee wrote: > >> >> > Update fuse to translate uids and gids to/from the user namspace > >> >> > of the process servicing requests on /dev/fuse. Any ids which do > >> >> > not map into the namespace will result in errors. inodes will > >> >> > also be marked bad when unmappable ids are received from > >> >> > userspace. > >> >> > > >> >> > Due to security concerns the namespace used should be fixed, > >> >> > otherwise a user might be able to gain elevated privileges or > >> >> > influence processes that the user would otherwise be unable to > >> >> > manipulate. Thus the namespace of the mounting process is used > >> >> > for all translations, and this namespace is required to be the > >> >> > same as the one in use when /dev/fuse was opened. > >> >> > > >> >> > >> >> I'm not sure that this is necessary if my nosuid patch goes in, but I > >> >> also don't think it makes any sense to hold this up while we find a > >> >> perfect solution. > >> >> > >> >> Is there a decent way to extend this to different translation schemes in > >> >> the future (e.g. a flag at fs setup that could be used)? > >> > > >> > I think it would be possible to relax the translation scheme > >> > restrictions in the future, certainly that's easier than tightening down > >> > a looser restriction. I still favor picking one namespace to use for > >> > translation (surely that's how it would work with other filesystems > >> > anyway) rather than using the current namespace during /dev/fuse I/O. I > >> > did an implementation using the latter technique, and it's far more > >> > complex with no benefits that I can see. > >> > >> Long term, I think we'll want more flexible translations for > >> filesystems on removable media, even when both the mounter and the > >> accessing process are in the init user namespace. But this can wait. > > > > You've piqued my interest. What are you thinking of which would require > > this flexibility? > > > > For an easy example, if I stick a USB stick into my computer and copy > a file to it, I probably want the file to be owned by uid 0 in the FS > metadata (but still owned by me as reported by stat(2) and friends). > > For a more complex example, tools like Sandstorm (http://sandstorm.io) > probably want to use FUSE mounted by an outer (non-root) userns and > accessed from an inner userns. With your patches, this *might* work, > but it might also be a little tricky. This at least should work fine with my patches so long as the fuse mount has the allow_other option the inner userns is a descendant of the outer ns. I don't think there's anything tricky, though I do suspect you'll also want the default_permissions option. Thanks, Seth > > I can also see this ability being extremely useful for NFS and other > network filesystems, where keeping all the uids in sync is currently a > royal PITA. > > --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
