On 11/15/2013 12:54 AM, Andy Lutomirski wrote: > 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. > what you mean old kernels here? I saw patch "vfs: Lock in place mounts from more privileged users" is merged into upstream in linux 3.12-rc1, this is not very old. I think there are not many userspace processes rely on this feature. If user think host needs to be secure, he should use MS_LOCK to mount filesystem. we can't make decison for user. Thanks -- 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
