oss-sec mailing list archives
Re: Multiple disputed issues in util-vserver
From: Fiedler Roman <Roman.Fiedler () ait ac at>
Date: Mon, 15 Dec 2014 18:00:54 +0000
Von: Fiedler Roman [mailto:Roman.Fiedler () ait 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 [2] 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/TtyPushbackPrivilegeEscalationYes, 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)
tointeract 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 shelltoavoid injection of shell commands Regarding documentation I would even vote for a solution d), that allthosetools get a mandatory argument like '--i-know-entering-insecure-container-may-kill-my-host' so that it isnotvery 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.htmlThis 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.
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Current thread:
- Multiple disputed issues in util-vserver Fiedler Roman (Oct 14)
- Re: Multiple disputed issues in util-vserver Carlos Alberto Lopez Perez (Oct 20)
- AW: Multiple disputed issues in util-vserver Fiedler Roman (Oct 21)
- <Possible follow-ups>
- Re: Multiple disputed issues in util-vserver Fiedler Roman (Dec 15)
- Re: Multiple disputed issues in util-vserver Carlos Alberto Lopez Perez (Oct 20)