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Message-ID: <87a95i57g9.fsf@x220.int.ebiederm.org> Date: Mon, 29 Sep 2014 16:32:22 -0700 From: ebiederm@...ssion.com (Eric W. Biederman) To: Andrey Wagin <avagin@...il.com> Cc: LKML <linux-kernel@...r.kernel.org>, Serge Hallyn <serge.hallyn@...onical.com>, linux-fsdevel@...r.kernel.org, Alexander Viro <viro@...iv.linux.org.uk> Subject: Re: Does MNT_LOCKED work as expected? Andrey Wagin <avagin@...il.com> writes: > Hi All, > > I think I found a case, when MNT_LOCKED (5ff9d8a65ce8 "vfs: Lock in > place mounts from more privileged users") doesn't help to hide > overmounted parts from unprivileged users. > The problem exists for mounts, which are not overmounted entirely. In > such cases we can open a directory from a target mount, which is not > overmounted. Then we do pivot_root to move all mounts in a temporary > directory. At the final step we deatch all mounts from the temporary > directory. After that all children mounts are umounted from the target > mount and we can use our file descriptor to open files, which have > been overmount before. > > Here is a example https://github.com/avagin/userns_vs_mntns. I am looking at this now to make certain I am understand what you are seeing but so far it looks like lazy unmounts allow you to bypass MNT_LOCKED :( Grumble. Eric -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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