linux-kernel - Re: tmpfs support of xattrs?

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Message-Id: <1225139131.31818.51.camel@moss-spartans.epoch.ncsc.mil>
Date:	Mon, 27 Oct 2008 16:25:31 -0400
From:	Stephen Smalley <sds@...ho.nsa.gov>
To:	Rob MacKinnon <c4blem0nkey@...il.com>
Cc:	Andreas Gruenbacher <agruen@...e.de>, hpa@...or.com,
	hugh@...itas.com, linux-kernel@...r.kernel.org,
	rob.mackinnon@...il.com, Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: tmpfs support of xattrs?

On Mon, 2008-10-27 at 13:14 -0700, Rob MacKinnon wrote:
> Andreas Gruenbacher wrote:
> > On Sunday, 26 October 2008 13:26:35 Hugh Dickins wrote:
> >> On Sat, 25 Oct 2008, Rob MacKinnon wrote:
> >>> The background: So during the initial configuration of a box I enabled
> >>> the xattr flags for ext3 and options of xattr in coreutils, and at the
> >>> time didn't realize that I'd hit a snag that would finally annoy me
> >>> enough after a month of getting a non-fatal error messages from cp "cp:
> >>> listing attributes of `/dev/null`: Invalid argument" to spend half a day
> >>> researching the cause and a potential solution.
> >>>
> >>> Setup: udev mounts a tmpfs to /dev then fills it with device nodes.
> >>> Problem: the resulting tmpfs has no xattr support.
> >>> Therefore: Tmpfs without xattrs, and coreutils  and everywhere else with
> >>> xattr support, cp freaks.
> >>>
> >>> Is there sometime in the forseable future when the tmpfs module will
> >>> support for xattrs in the stable branch, or should I "holler at the
> >>> maintainers of coreutils to fix their broken code in cp". Even better
> >>> (and I like this option the most) a little of both?
> >> I've not seen "cp: listing attributes of `/dev/null': Invalid argument"
> >> messages (or.. do I have a dim recollection of them once upon a time?).
> >> I would certainly get irritated by them if I did, and want to fix them.
> >> I tried "cp /dev/null temp" on a few distros just now but not seen it.
> > 
> > As Hugh pointed out already, tmpfs does support xattrs since quite a while, so 
> > enabling that should fix the symptoms. Independent of that, cp must of course 
> > work correctly on filesystems that don't have xattrs. Those filesystems are 
> > not supposed to return EINVAL, though.
> > 
> > Could you please run cp under strace to show us what's happening at the 
> > syscall level (and perhaps under ltrace in addition to see the library level 
> > as well)?
> > 
> > If the error happens at the syscall level (*listxattr), then which kernel is 
> > it exactly, and where can I find its sources?
> > 
> 
> Thanks Andreas, Hugh & HPA
> 
> First off, thanks for looking into this.  After googling around, hitting
> forums and such and not getting any answers, this list seemed the best
> place to come to ask.
> 
> Now onward to business...I can say that I too was under the general
> understanding that xattr for tmpfs was added at 2.6.10...and was still
> currently supported.  Unfortunately I already have the config flags set
> (as seen below, for a full config set attached) so there is a continued
> confusion in my mind why this is still plaguing me.
> 
> I've had several friends compare what was going on, and of them they
> were all running rhel and cent (most with no udev support so the
> comparison didn't help at all).
> 
> I'll start out with distro info and the like...
> `uname -a`="Linux shin-yuko 2.6.26-gentoo-r2 #1 SMP PREEMPT Wed Oct 22
> 16:31:40 PDT 2008 i686 Intel(R) Pentium(R) 4 CPU 2.80GHz GenuineIntel
> GNU/Linux"
> 
> coreutils-version="coreutils-6.12-r2"
> 
> My current config does have the following set:
> 	CONFIG_TMPFS=y
> 	CONFIG_TMPFS_POSIX_ACL=y
> 	CONFIG_SHMEM=y
> 
> Output from `strace /bin/cp /dev/null /root/temp`= #see attachment
> Output from `ltrace -CS /bin/cp /dev/null /root/temp`= #see attachment
> 
> Output from `attr -l /dev/null`=Segfault (hmmm...lemme look at a strace
> and ltrace of that too)
> 
> `strace attr -l /dev/null`= #see attachment
> `ltrace -CS /bin/attr -l /dev/null`= #see attachment
> 
> Kernel source can be attained from:
> http://distfiles.gentoo.org/distfiles/linux-2.6.26.tar.bz2
> 
> Patches:
> http://sources.gentoo.org/viewcvs.py/linux-patches/genpatches-2.6/trunk/2.6.26/
> 
> I know this is silly but, setfattr and getfattr obviously don't work
> either...just thought it was worth mentioning.

Looks like a bug in Smack's implementation of the inode_listsecurity
hook to me.  Did you mean to enable Smack in your kernel config?

-- 
Stephen Smalley
National Security Agency

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