On Thu, Sep 05, 2013 at 01:39:26PM -0400, Vivek Goyal wrote: > On Thu, Sep 05, 2013 at 10:47:15AM -0400, Vivek Goyal wrote: > > On Thu, Sep 05, 2013 at 02:40:39PM +0000, Matthew Garrett wrote: > > > On Wed, 2013-09-04 at 20:49 -0400, Vivek Goyal wrote: > > > > > > > I did what Eric Biederman suggested. I first unshare the mount namespace > > > > of /sbin/kexec from parent. Then I disable any event propogation between > > > > mounts. Then I lazy unmount existing /proc and /sys and remount them. I > > > > think this should make sure that we are seeing at /proc and /sys as > > > > exported by kenrel? > > > > > > Namespaces have mostly been used with the assumption that namespaces > > > contain child processes, rather than parent processes attacking > > > children. Are we guaranteed that (barring ptrace) a parent process is > > > unable to manipulate a child's namespaces? > > > > This is a good question and I don't know enough about namespaces to > > be able to answer it. > > > > I am CCing Eric Biederman and he should have an Idea. > > > > Eric, > > > > So this is in context of kdump an secureboot. We were discussing to be > > able to create a private mount namespace for /sbin/kexec and remount > > /proc/ and /sys so that /sbin/kexec is sure that it is looking at > > something as exported by kernel. > > > > Is it possible for unsigned parent to now maninpulate child /sbin/kexec > > mount namespace now? > > I am not an expert in this area. I am reading following two articles. > > http://man7.org/linux/man-pages/man2/mount.2.html > http://www.ibm.com/developerworks/linux/library/l-mount-namespaces/index.html > > I think once we did unshare() child got its own mount name space and > after that we converted it into a private mount point. I think that > will ensure that no mount events are propagated from parent to child > and vice-a-versa. I doubt that now there is any way a parent can > modify child's mount namespace. I asked this question to Al Viro. And he thinks it should be fine. He mentioned though that make sure /proc and /sys are not symlinks. Otherwise after I have remounted /proc, root could remove /proc symlink and replace with directory of his choice and fake proc files in that dir. He did mention that a new mount option to *not follow symlink* might make sense. Initially I thought I can do stat(/proc) and if it is not symlink then mount /proc. But I think it is racy as root could replace /proc in between the symlink check and mount operation. I will see if I can write a patch to introduce new mount option. Thanks Vivek _______________________________________________ kernel mailing list kernel@xxxxxxxxxxxxxxxxxxxxxxx https://admin.fedoraproject.org/mailman/listinfo/kernel
