Date: Mon, 15 Dec 2014 18:00:54 +0000 From: Fiedler Roman <Roman.Fiedler@....ac.at> To: "oss-security@...ts.openwall.com" <oss-security@...ts.openwall.com> Subject: Re: Multiple disputed issues in util-vserver > Von: Fiedler Roman [mailto:Roman.Fiedler@....ac.at] > > [Snip] > > > > Issue 3: It seems that handling of open tty FDs on enter, that allows to > > > inject arbitrary keyboard input to be read by the parent process, also > > > affects the tool to start the guest container. This seems to be the same > > > issue with "vserver start" as reported in  for vserver enter, which > > > was classified as less relevant back than. My rating would be little lower > > > than 2 but still quite high for mass hosting: manual restart, e.g. during > > > maintenance, seems quite common to me. > > > > > > > If I understand correctly, this (and the previous one) are > > CVE-2005-4890, isn't it?. > > > > http://www.halfdog.net/Security/2012/TtyPushbackPrivilegeEscalation > > Yes, this is the stuff about the general problem, this issue is quite a > similar one for su. In both cases (su and vserver), a tool used to enter an > possibly compromised, lower privileged context from a higher privileged one > fail. > > The CVE is only for su. For su it seems, that the issue is treated more a > bug than expected feature, but it seems, that it is still not fixed for > current Ubuntu release. > > For vserver ... > > > > From my point of view, those issues might be expected behavior as claimed by > > > the developers, ....> > > > this is the state of discussion, so no bug. > > > ... but if so it should be at least stated more clearly in > > > documentation: > > > > > > a) never use any tools except vserver stop (to terminate the container) > to > > > interact with a running and possibly compromised container from the host > > > b) only use network/socket-based tools to connect to processes inside a > > > possibly compromised guest, e.g. SSH. > > > c) never start a possibly compromised container from interactive shell > to > > > avoid injection of shell commands > > > > > > Regarding documentation I would even vote for a solution d), that all > those > > > tools get a mandatory argument like > > > '--i-know-entering-insecure-container-may-kill-my-host' so that it is > not > > > very likely, that someone will use those tools for something else then > > > testing or nice-world administration. > > > > > > Opinions to issues 1-3? > > > > > > What about solutions? > > > > Halfdog (CC'ed) already suggested some possible solutions: > > http://www.paul.sladen.org/vserver/archives/201211/0011.html > > This should handle the pty issues. But since it requires the admin not to > forget to use the manual workaround EVERY TIME, therefore man page update > should be done in any case. Fix with pty allocation (or detaching from pty > for vserver start) would be best solution. Without technical fix a > "--do-it-insecure" parameter would make it clear on command line, that I > want to proceed knowing the risks. As there was not really much feedback from the vserver side and as there are quite more issues with vserver I hoped to get rid of all those issues using LXC. At least issue 3 is also with lxc-attach is quite the same, but documentation of lxc-attach does not mention the risks either (at least on Ubuntu). Calling # lxc-attach --name buildhost-trusty -- /bin/ls will create file outside when e.g. /bin/ls was replaced with /root/TtyPushbackSignaling --NoSignal -- "touch /xxx" So I guess one should not use attach to run e.g. automatic updates in the guest or something alike. Download attachment "smime.p7s" of type "application/pkcs7-signature" (6344 bytes)
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