Date:   Tue, 28 Apr 2020 18:48:24 +0200
From:   Jan Kara <jack@...e.cz>
To:     "Darrick J. Wong" <darrick.wong@...cle.com>
Cc:     Jan Kara <jack@...e.cz>, Francois <rigault.francois@...il.com>,
        linux-ext4@...r.kernel.org
Subject: Re: ext4 and project quotas bugs

On Tue 28-04-20 08:53:51, Darrick J. Wong wrote:
> On Tue, Apr 28, 2020 at 05:32:28PM +0200, Jan Kara wrote:
> > Hello!
> > 
> > On Tue 28-04-20 08:41:59, Francois wrote:
> > > hello! I was just giving ext4 project quotas a try. Definitely not the
> > > most used ext4 feature (I was the first to answer a stackoverflow
> > > question on it in https://stackoverflow.com/a/61465057/2852464).
> > > Quotacheck tells me to mail you the bugs :D so I do
> > 
> > Sure :) Generally for ext4 issues (including project quotas) you can also
> > ask at linux-ext4@...r.kernel.org (added to CC so that the discussion is
> > archived for other people).
> > 
> > > my goal is to make some kind of ansible playbook to install project
> > > quotas, so I am interested in using a tool like setquota, I also want
> > > the teams behind the capped directories, to think about a clean-up
> > > mechanism (the quota would just be a temporary annoyance for them), so
> > > it should not be "jailbreakable" too easily.
> > 
> > Hum, that "not jailbreakable" part is going to be difficult unless you also
> > confine those users also in their user namespace. Because any user is
> > allowed to change project ID of the files he owns arbitrarily if he is
> > running in the initial user namespace. Project quotas have been designed as
> > an advisory feature back in Irix days... There are talks of allowing to
> > tweak the behavior (i.e., to allow setting of project id only by sysadmin)
> > by a mount option but so far nobody has implemented it.
> > 
> > > quota-4.05-3.1.x86_64
> > > Linux localhost 5.6.2-1-default #1 SMP Thu Apr 2 06:31:32 UTC 2020
> > > (c8170d6) x86_64 x86_64 x86_64 GNU/Linux
> > > CPE_NAME="cpe:/o:opensuse:tumbleweed:20200413"
> > > 
> > > 1- quotacheck fails with quotacheck: Cannot find filesystem to check
> > > or filesystem not mounted with quota option.
> > > prjquota is enabled using extended mount options but quotacheck seems
> > > to ignore this
> > > # tune2fs -l /dev/loop0 | grep -i mount\ opt
> > > Default mount options: user_xattr acl
> > > Mount options: prjquota
> > > 
> > > (also, shouldn't these mount options be reflected in /proc/mounts?)
> > 
> > Yes and that's deliberate. Unlike user and group quotas, project quotas are
> > only supported when stored in hidden system files (user and group quotas
> > are also supported in that way when you create ext4 with 'quota' feature).
> > So checking of quotas is handled by e2fsck and quotacheck has no way to
> > influence them.
> 
> How /does/ one enable whatever the latest iteration on quota is in ext4?
> IIRC the old VFS method (independent non-journalled quota files in the
> root dir) is deprecated, which means that the preferred method now is:
> 
> # mkfs.ext4 -O quota -E quotatype=usrquota:grpquota:prjquota /dev/fd0
> 
> right?

Yes.

> > > 2- project quota are a bit too easy to escape:
> > > dd if=/dev/zero of=someoutput oflag=append
> > > loop0: write failed, project block limit reached.
> > > dd: writing to 'someoutput': Disk quota exceeded
> 
> EDQUOT?  Hrm, XFS usually returns ENOSPC for project quotas, since we
> also change the statfs output to make it look like the the mount size is
> the project quota's hard limit.

Yeah, we don't specialcase project quotas (just another quota type) in the
fs/quota/ and so errors are the same for all of them...

> > > 2467+0 records in
> > > 2466+0 records out
> > > 1262592 bytes (1.3 MB, 1.2 MiB) copied, 0.0105432 s, 120 MB/s
> > > vagrant@...alhost:/mnt/loop/abc/mydir3> chattr -p 33 someoutput
> > > vagrant@...alhost:/mnt/loop/abc/mydir3> dd if=/dev/zero of=someoutput
> > > oflag=append
> > > dd: writing to 'someoutput': No space left on device
> > > 127393+0 records in
> > > 127392+0 records out
> > > 65224704 bytes (65 MB, 62 MiB) copied, 0.568859 s, 115 MB/s
> > 
> > Yes and as I mentioned above this is deliberate.
> > 
> > > 3- project id '-1" yields fun results:
> > > 
> > > chattr +P -p -1 .
> 
> Heh, that command doesn't work on xfs.  Weird, more kernel bugs to chase...

Yeah, unlike ext4 xfs refuses to set PROJINHERIT flag through SETFLAGS
ioctl which is what makes this command fail. But I don't see anything in
the handling of XFS_IOC_FSSETXATTR that would prevent setting of this
invalid project id...

Hum, after some debugging what I believe is failing is dquot_init() call
which tries to initialize project quotas for a new inode, calls
qid_has_mapping() from dqget() for this -1 project ID, gets error back
(ultimately from map_id_up()) and so dget() fails with -EINVAL which gets
propagated out to userspace.
 
> > > dd if=/dev/zero of=someoutput oflag=append
> > > dd: failed to open 'someoutput': Invalid argument
> > 
> > Yes, that's a bug that should be fixed. Thanks for reporting this! -1 means
> > 'this id is not expressible in current user namespace' and some code gets
> > confused along the way. We should refuse to set project -1 for a file...
> 
> Awkward part: projid 4294967295 is allowed on XFS (at least by the
> kernel), though the xfs quota tools do not permit that.

Are you OK with just refusing to set projid 4294967295 for everybody? Or
should we just not try to translate project IDs through user namespaces?
Because XFS does not seem to translate them while ext4 does... What a mess.

								Honza

-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR

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