On Thu, Nov 14, 2013 at 3:10 AM, Gao feng <gaofeng@xxxxxxxxxxxxxx> wrote: > On 11/13/2013 03:26 PM, Gao feng wrote: >> On 11/09/2013 01:42 PM, Eric W. Biederman wrote: >>> Right now I would rather not have the empty directory exception than >>> remove this code. >>> >>> The test is a little trickier to write than it might otherwise be >>> because /proc and /sys tend to be slightly imperfect filesystems. >>> >>> I think the only way to really test that is to call readdir on the >>> directory itself :( I don't like that thought. >>> >>> I don't know what I was thinking when I wrote that test but I definitely >>> goofed up. Grr! >>> >>> I can certainly filter out any directory with nlink > 2. That would be >>> an easy partial step forward. >>> >>> The real question though is how do I detect directories it is safe to >>> mount on where there will not be files in them. I can't call iterate >>> with the namespace_lock held so things are a bit tricky. >>> >> >> I know this problem is not easy to be resolved. why not let the user >> make the decision? maybe we can introduce a new mount option MS_LOCK, >> if user wants to use mount to hide something, he should use mount with >> option MS_LOCK. so the unpriviged user can't umount this filesystem and >> fail to mount the filesystem if one of it's child mount is mounted with >> MS_LOCK option otherwise he use MS_REC too. >> > > Something like this. > > From 437f33ea366623c7a9d557b2e84cae424876a44f Mon Sep 17 00:00:00 2001 > From: Gao feng <gaofeng@xxxxxxxxxxxxxx> > Date: Wed, 13 Nov 2013 16:06:46 +0800 > Subject: [PATCH] userns: introduce new mount option MS_LOCK > > After commit 5ff9d8a65ce80efb509ce4e8051394e9ed2cd942 > vfs: Lock in place mounts from more privileged users, > in userns, the mounts of child mntns which copied from > parent mntns is locked and user has no rights to umount/move > them, it's too strict. > > The core purpose of above commit is trying to prevent > unprivileged user from accessing files hidden by mount. > This patch introduces a new mount option MS_LOCK, this > gives user the capable to mount filesystem as the type > of lock if he wants to use mount to hide something. > This is bad -- if something was secure in old kernels, it needs to stay secure. If you had MS_NOT_A_LOCK, that would be okay, but it might not solve your problem. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
