Re: [PATCH 0/7] overlay filesystem v9
From: Miklos Szeredi
Date: Thu May 19 2011 - 13:44:45 EST
Andy Whitcroft <apw@xxxxxxxxxxxxx> writes:
> On Tue, May 17, 2011 at 02:30:45PM +0200, Miklos Szeredi wrote:
>> Here's an updated version of the overlay filesystem.
>> Git tree is here:
>> git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs.git overlayfs.v9
> Ok I pulled this into the Ubuntu kernel and made an Ubuntu Live CD
> for testing. Overall it worked pretty well, no hangs, no crashes,
> performance seemed reasonable. We hit one issue with hard links which
> fail to be possible on overlayfs mounts when the Yama LSM (out of tree)
> is enabled. This module applies more aggressive checks on hard-links
> preventing links to files you cannot read.
Great, thanks for testing.
> The bug seems to be related to the way we handle user and group owners for
> the overlayfs inodes, which we do not initialise (and they remain as 0,0).
> While these ownerships are never exposed to userspace they are exposed
> to the LSM layer, and the LSM module checks the wrong owner and fails
> to allow the links.
> From what I can see it is completly reasonable to initialise the ownership
> fields in the overlayfs inode from the underlying inode, or for new files
> ones initialise it in the normal way based on the containing directory.
> Now I am nothing like a filesystems expert but looking at what other
> filesystems do I think the patch below is sufficient, but certainly it
> needs some sanity checking. At least it fixes all the issues I see
Forgot to attach the patch?
> With this in place I have been able to boot a Natty release live CD
> image, and upgrade it in place to the latest and greatest of everything.
> Very nice. Thanks for your work continuing work on overlayfs. It is
> starting to look good enough to merge.
I'd be happier if the LSM module were fixed not to peek inside the inode
structure. Some filesystems (notably network ones) do not guarantee i_*
to be up-to-date, relying on these is not a good idea.
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/