Messages in this thread | | | Date | Sat, 29 Jun 2013 21:45:46 -0500 | From | Rob Landley <> | Subject | Re: [PATCH 1/5] initmpfs: replace MS_NOUSER in initramfs |
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On 06/29/2013 08:15:40 PM, Eric W. Biederman wrote: > Rob Landley <rob@landley.net> writes: > > > From: Rob Landley <rob@landley.net> > > > > Mounting MS_NOUSER prevents --bind mounts from rootfs. Prevent new > rootfs > > mounts with a different mechanism that doesn't affect bind mounts. > > I don't see patches 4 and 5 so I don't know if you have covered this > elsewhere but a very important part of the reason for MS_NOUSER is to > prevent unmounting of rootfs.
Actually rootfs has separate protections against umounting. I tried several varieties of "umount -f /" and "cd /; umount -l .; umount -f .." and so on; they're all ignored.
> The entire vfs breaks if you are allowed to unmount rootfs, and it > appears this patch is allowing that.
Yes, I hit that many moons ago. (Doing either mount --move or pivot_root on initramfs, and then umounting it once it was in a subdirectory: system locked hard; I can try to dig up a link if you like, it was something like 2005? Maybe 2.6.11? It got fixed. This was before I implemented switch_root in busybox, because the experience is what taught me the difference between pivot_root and switch_root.)
I tested "mount --bind / home" on initmpfs and got "invalid argument". (Haven't tried pivot_root again because that binary's not on my test system, but when you're _not_ on rootfs that'll kill the system if you do it in the global namespace without knowing what you're doing. I can specifically test that if you like...)
Rob
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