linux-kernel - Re: tmpfs support of xattrs?

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Message-ID: <49062BD5.5050802@gmail.com>
Date:	Mon, 27 Oct 2008 14:00:05 -0700
From:	Rob MacKinnon <c4blem0nkey@...il.com>
To:	Stephen Smalley <sds@...ho.nsa.gov>
CC:	rob.mackinnon@...il.com, Andreas Gruenbacher <agruen@...e.de>,
	hpa@...or.com, hugh@...itas.com, linux-kernel@...r.kernel.org,
	Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: tmpfs support of xattrs?

Stephen Smalley wrote:
> 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?
> 

I had intensionally flipped CONFIG_SECURITY_SMACK to "y".  I'm used to
running hardened with GRSec and RBAC (ot: but found the gentoo
versioning was so far behind / and me being lazy and not wanting to
manually do the patching / I dropped using hardened sources) so when I
saw the option for what sounded like a good compromise I jumped at it.
Looks like I did a good thing too having uncovered a problem. :)

-- Rob
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