Re: [libvirt] [RFC PATCH 2/2] LXC: Create ro overlay mounts only if we're not within a user namespace

On Mon, Jul 01, 2013 at 01:05:23PM +0200, Richard Weinberger wrote: > Am 01.07.2013 12:33, schrieb Daniel P. Berrange: >> On Mon, Jul 01, 2013 at 08:29:14AM +0200, Richard Weinberger wrote: >>> Any ideas what's going on here? >> >> No, it is very odd. It smells like a kernel issue to me. What >> version are you running ? > > I see this issue on all kernels. > Currently I'm using vanilla v3.9.x and v3.10. > >> I've also tried running the demo programs shown on the LWN.net >> article >> >> https://lwn.net/Articles/532593/ >> >> and they don't operate in the way described by the article - the demo >> programs continue to ru as 'nfsnobody' even after the mappings are >> setup. >> >> I'm just using the Fedora 3.9.4-303 kernel, rebuilt with userns enabled >> in KConfig. I'm wondering if there is still stuff missing in 3.9.x >> that prevents this from working properly, or if the kernel behaviour >> changed after those LWN articles were written. > > To me it looks like the capability system behaves odd. > The mappings in /proc are fine as long I do not call capng_updatev(). > Also calling capng_updatev() with parameters that do not change the current cap set > triggers the odd behavior too. > > So we see two (related?) issues: > 1. If we try updating the capabilities of pid1 /proc/1/ has unmapped files till we exec(). > 2. Dropping capabilities does not work we always gain a fresh and full capability set. > > BTW: I'm sure the issues are not caused by Gau Feng's userns patches. Yeah, I've reproduced this problem with standalone code outside of libvirt. Take the attached code and run