On July 9, 2016 4:26:28 PM GMT+09:00, Andrew Vagin <avagin@xxxxxxxxxxxxx> wrote: >On Fri, Jul 08, 2016 at 10:05:18PM -0500, Eric W. Biederman wrote: >> James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> writes: >> >> > On Fri, 2016-07-08 at 18:52 -0500, Eric W. Biederman wrote: >> >> James Bottomley <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> writes: >> >> >> >> > On July 8, 2016 1:38:19 PM PDT, Andrew Vagin ><avagin@xxxxxxxxxxxxx> >> >> > wrote: >> >> >> >> > > What do you think about the idea to mount nsfs and be able to >> >> > > look up any alive namespace by inum: >> >> > >> >> > I think I like it. It will give us a way to enter any extant >> >> > namespace. It will work for Eric's fs namespaces as well. >Perhaps >> >> > a /process/ns/<inum> Directory? >> > >> > As you understood, I meant /proc/ns/<inum> (damn mobile phone >> > completions). >> > >> >> *Shivers* >> >> >> >> That makes it very easy to bypass any existing controls that exist > >> >> for getting at namespaces. It is true that everything of that >kind >> >> is directory based but still. >> >> >> >> Plus I think it would serve as information leak to information >> >> outside of the container. >> >> >> >> An operation to get a user namespace file descriptor from some >kernel >> >> object sounds reasonably sane. >> >> >> >> A great big list of things sounds about as scary as it can get. >This >> >> is not the time to be making it easier to escape from containers. >> > >> > To be honest, I think this argument is rubbish. If we're afraid of >> > giving out a list of all the namespaces, it means we're afraid >there's >> > some security bug and we're trying to obscure it by making the list >> > hard to get. All we've done is allayed fears about the bug but the >> > hackers still know the portals to get through. >> > >> > If such a bug exists, it will be possible to exploit it by simply >> > reconstructing the information from the individual process >directories, >> > so obscurity doesn't protect us and all it does is give us a false >> > sense of security. If such a bug doesn't exist, then all the >security >> > mechanisms currently in place (like no re-entry to prior namespace) >> > should protect us and we can give out the list. >> > >> > Let's deal with the world as we'd like it to be (no obscure >namespace >> > bugs) and accept the consequences and the responsibility for fixing >> > them if we turn out to be slightly incorrect. We'll end up in a >far >> > better place than security by obscurity would land us. >> >> No. That is not the fear. The permission checks on >/proc/self/ns/xxx >> are different than if the namespace is bind mounted somewhere. >> >> That was done deliberately and with a reasonable amount of >forethought. >> You are asking to throw those permission checks out. The answer is >no. >> >> Furthermore there is a much clearer reason not to go with a list of >all >> namespaces. A list of all namespaces breaks CRIU. As you have >described >> it the list will change depending upon which machine you restore a >> checkpoint on. I honestly don't know what kind of havoc that will >cause >> but it is certainly something we won't be able to checkpoint no >matter >> how hard we try. > >It's right. I hadn't thought about this. Me neither. Sorry for the prior outburst. I think this means we're back to exposing owning userns in the /proc /<pid >/ns directory. >> >> A global list of namespaces especially of the kind that you can open >> and get a handle to the namespace is just not appropriate. >> >> I know inode numbers comes darn close to names but they aren't really >> names and if it comes to it we can figure out how to preserve an >> applications view of it all across a checkpoint/restart. So far it >> hasn't proven necessary to preserve any inode numbers across >> checkpoint/restart but again it is theoretically possible if it >becomes >> necessary. >> >> Throwing away checkpoint/restart support for the sake of >> checkpoint/restart is a no-go. >> >> Containers fundamentally imply you don't have global visibility, >> and that is a good thing. > >All these thoughts about security make me thinking that kcmp is what we >should use here. It's maybe something like this: > >kcmp(pid1, pid2, KCMP_NS_USERNS, fd1, fd2) > >- to check if userns of the fd1 namepsace is equal to the fd2 userns > >kcmp(pid1, pid2, KCMP_NS_PARENT, fd1, fd2) > >- to check if a parent namespace of the fd1 pidns is equal to fd pidns. > >fd1 and fd2 is file descriptors to namespace files. > >So if we want to build a hierarchy, we need to collect all namespaces >and then enumerate them to check dependencies with help of kcmp. Sure, but we need a method for opening the filehandles first .. . James >> >> Eric -- Sent from my Android device with K-9 Mail. Please excuse my brevity. -- 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
