On Tue 05-07-16 09:55:18, Eric W. Biederman wrote: > Jan Kara <jack@xxxxxxx> writes: > > > On Sat 02-07-16 12:20:31, Eric W. Biederman wrote: > >> It is expected that filesystems can not represent uids and gids from > >> outside of their user namespace. Keep things simple by not even > >> trying to create filesystem nodes with non-sense uids and gids. > >> > >> Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> > > > > So if we have sb->s_user_ns that doesn't map UID and GID 0, root cannot > > directly create files in this filesystem. EOVERFLOW error will at least > > hint us where the problem is but still I'm suspecting this is going to > > create hard to debug configuration issues... I'm not sure if we can do > > anything about this but I wanted to point it out. > > A reasonable point. > > A couple of details. > > - If there is no uid or gid 0 inside of a user namespace there is > no root user in that namespace so this is a moot point. > > - If we are talking about uid 0 in the initial user namespace the > scenario you are worried about can occur, but you have to work at it > to get into that situation. > > To create a superblock has s_user_ns != &init_user_ns something like > the following has to occur. > > setuid(1000); > unshare(CLONE_NEWUSER); > unshare(CLONE_NEWNS); > mount(....); > > At which point the oridinary root user can not see the filesystem > with s_user_ns != &init_user_ns as it is located in another mount > namespace. > > Which means root has to use setns to get into that mount namespace, > so there are going to be larger hints than -EOVERFLOW. OK, I see. Thanks for explanation. The inability of the admin (UID 0 in init_user_ns) to easily see and change any filesystem mounted in the system makes me somewhat nervous ;). But I guess the complexity is the price for the flexibility... Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
