[Unionfs] unionfs has problems with file permissions

[Johannes Hirte]

Am Wed, 4 Feb 2009 21:56:26 -0500
schrieb Erez Zadok <ezk at cs.sunysb.edu>:

> Johannes, I've tried the procedure again today and was still unable to
> reproduce it.  I tried it with unionfs-2.5 and 2.5.1 on 2.6.27.10.  I
> followed your descriptions precisely as per the URL below (one nfs-ro
> branch, set as ro in unionfs and copyup to a rw branch).  In my case,
> strace showed this for the "echo >test" command:
> 
> open("test", O_WRONLY|O_CREAT|O_TRUNC|O_LARGEFILE, 0666) = 3
> 
> Since you've tried many kernel version, I don't think it's the linux
> kernel.

It seems to be distribution specific. I've tested with gentoo
(unstable) now, and it works well. Testcase was a ro mounted local
filesystem together with a rw mounted tmpfs. No problems so far. Tested
with linux-2.6.28.4 + unionfs-2.5.1.

> 1. What can you tell me about your NFS server?  What OS and OS
> version is it?  What version of the NFS proto do you use (2? 3? 4?)
> and what transport (udp? tcp)?  I'll try to reproduce the conditions
> exactly on my end.

The server is Mandriva 2007.0 based, the client is 2008.1 based.
NFS-Version 3 with tcp is used. But I'm not sure that NFS is the reason
for the problems. 

> 2. Are your kernels pretty much vanilla or is there something special
> about them like additional non-mainline patches applied that could
> affect things (e.g., tomoyo, rt-linux, etc.).  If your kernels
> differ, please give me a tarball of your kernel sources and
> your .config.

It's a plain vanilla kernel with the unionfs patch.

> 3. I'd like to get your kernel .config to see if you turned on any
> other options that could make a difference (esp. extra security
> stuff).  Do you use ACLs, SElinux, or the like?  Those are the kinds
> of things that can effect permission checking.

Configs from the Gentoo testsystem (2.6.28.4) and the Mandriva based
netboot system (2.6.24.4) are attached. I will do some more tests on
this, cause the configs differ very much for now. 
 
> 4. Any chance I can get a temp ssh access to a system you have that
>    demonstrates this?  In my experience, a 5 minute poking around a
> system can save everyone many hours/days of emails and attempts to
> second guess each other.

I will try to find a system we can make accessible outside from our
network.

> BTW, if you haven't already, can you open a bugzilla report on this
> (https://bugzilla.filesystems.org/), then upload logs and config
> files as needed; others who've seen a similar issue can ask to be
> CC'ed on that bugzilla report, so we don't have to innundate the ML
> with a barrage of "can you try XYZ now" messages. :-)

Will do so.
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