James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> writes: > On Mon, 2016-04-18 at 19:11 +0200, Karel Zak wrote: >> On Mon, Apr 18, 2016 at 11:37:34AM -0400, James Bottomley wrote: >> > OK, so if you want me to reply properly, you're going to have to keep >> > my address in the cc list. >> > >> > > > If you enter it first, you lose privilege for subsequent >> > > namespace >> > > > enters,see issue >> > > > >> > > > https://github.com/karelzak/util-linux/issues/315 >> > > > >> > > > The fix is to enter the user namespace last of all. >> > > >> > > I verified that with *current*/unpatched nsenter, >> > > >> > > $ unshare -rm sleep inf & >> > > $ nsenter -t $! -U -m --preserve >> > > >> > > works as expected (from regular user [and with unprivileged userns >> > > enabled]). >> > > >> > > With this patch it *won't* work [verified], of course (as you'll need >> > > root privileges in userns before joining mount-ns, and you can only >> > > obtain them by entering userns first). >> > >> > So we're using userns for different things. I'm using it to remove >> > privilege (so on my userns implementation root in the host enters but >> > on becoming root in the userns, it can do nothing other than write to >> > its own files) and you're using it to enhance privilege. It looks like >> > these two things will always be mutually exclusive, so perhaps we need >> > an extra flag to nsenter to say do the userns first or last? >> >> That's what I have talked about at github -- see Eric's comment in the >> code, the user NS is the first in the array for a good reason. May be >> it would be really better to add --user-{first,last} options to >> specify when you want to enter user NS. > > OK, I'll code this up; hang on. I think we can do this even better with two passes to setns. A first pass before the user namespace is set (that ignores failures), and a second pass that sets the user namespace first as happens today. That should satisfy both cases without flags, and would remove the need to remember/guess which kind of container people are using. Eric -- To unsubscribe from this list: send the line "unsubscribe util-linux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
