On 2016/02/18 11:57, Eric W. Biederman wrote: > > Ccing The containers list because a related discussion is happening there > and somehow this thread has never made it there. > > Ian Kent <raven@xxxxxxxxxx> writes: > >> On Mon, 2013-11-18 at 18:28 +0100, Oleg Nesterov wrote: >>> On 11/15, Eric W. Biederman wrote: >>>> >>>> I don't understand that one. Having a preforked thread with the >>>> proper >>>> environment that can act like kthreadd in terms of spawning user >>>> mode >>>> helpers works and is simple. >> >> Forgive me replying to such an old thread but ... >> >> After realizing workqueues can't be used to pre-create threads to run >> usermode helpers I've returned to look at this. > > If someone can wind up with a good implementation I will be happy. > >>> Can't we ask ->child_reaper to create the non-daemonized kernel thread >>> with the "right" ->nsproxy, ->fs, etc? >> >> Eric, do you think this approach would be sufficient too? >> >> Probably wouldn't be quite right for user namespaces but should provide >> what's needed for other cases? >> >> It certainly has the advantage of not having to maintain a plague of >> processes waiting around to execute helpers. > > That certainly sounds attractive. Especially for the case of everyone > who wants to set a core pattern in a container. > > I am fuzzy on all of the details right now, but what I do remember is > that in the kernel the user mode helper concepts when they attempted to > scrub a processes environment were quite error prone until we managed to > get kthreadd(pid 2) on the scene which always had a clean environment. > > If we are going to tie this kind of thing to the pid namespace I > recommend simplying denying it if you are in a user namespace without > an approrpriate pid namespace. AKA simply not allowing thigns to be setup > if current->pid_ns->user_ns != current->user_ns. > Can't be handled by simple capability like CAP_SYS_USERMODEHELPER ? User_ns check seems not to allow core-dump-cather in host will not work if user_ns is used. Thanks, -Kame -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
