Date: Fri, 3 Apr 2015 12:58:02 +0200 From: Jann Horn <jann@...jh.net> To: oss-security@...ts.openwall.com Subject: Linux namespaces: It is possible to escape from bind mounts See here for the corresponding patches: <http://permalink.gmane.org/gmane.linux.kernel.containers/29173> <http://permalink.gmane.org/gmane.linux.kernel.containers/29177> Given that it went over a public mailinglist now, I guess there's not much sense in keeping it secret anymore. Containers on Linux normally use bind mounts to restrict how much of the filesystem is visible for processes inside the container. However, if an attacker can gain capabilities within such a container or can create another user and mount namespace within the existing container, he can do something similar to a double-chroot attack to break out of the bind mount and gain access to the full filesystem to which the bind mount refers: Create folders /A, /A/B, /C, /D inside the namespace. Bind-mount the /A inside the namespace to /D. Let a process chdir to /D/B. Move /D/B over into /C. The process which chdir'ed to /D/B is now in /C/B, but at the same time it is in a bind mount with /D as root. It can then traverse upwards, past what looks like / inside the namespace. Download attachment "signature.asc" of type "application/pgp-signature" (820 bytes)
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