linux-ext4 - Re: [PATCH 1/2] quota: Handle Q_GETNEXTQUOTA when quota is disabled

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Date:	Mon, 4 Apr 2016 11:40:14 +0200
From:	Jan Kara <jack@...e.cz>
To:	Theodore Ts'o <tytso@....edu>
Cc:	Jan Kara <jack@...e.cz>, linux-ext4@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, ocfs2-devel@....oracle.com
Subject: Re: [PATCH 1/2] quota: Handle Q_GETNEXTQUOTA when quota is disabled

On Fri 01-04-16 10:39:56, Ted Tso wrote:
> On Tue, Mar 29, 2016 at 06:11:43PM +0200, Jan Kara wrote:
> > Currently we oopsed when Q_GETNEXTQUOTA got called when quota was
> > disabled. Properly check whether quota is enabled for the filesystem
> > before calling into quota format handler.
> > 
> > diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
> > index ba827daea5a0..ff21980d0119 100644
> > --- a/fs/quota/dquot.c
> > +++ b/fs/quota/dquot.c
> > @@ -2047,11 +2047,20 @@ int dquot_get_next_id(struct super_block *sb, struct kqid *qid)
> >  	struct quota_info *dqopt = sb_dqopt(sb);
> >  	int err;
> >  
> > -	if (!dqopt->ops[qid->type]->get_next_id)
> > -		return -ENOSYS;
> > +	mutex_lock(&dqopt->dqonoff_mutex);
> > +	if (!sb_has_quota_active(sb, qid->type)) {
> > +		err = -ESRCH;
> > +		goto out;
> > +	}
> > +	if (!dqopt->ops[qid->type]->get_next_id) {
> > +		err = -ENOSYS;
> > +		goto out;
> > +	}
> 
> Don't you also have to test if dqopt->ops[qid->type] is NULL?  e.g.,
> if the quota inode hasn't been loaded for that quota type?

Well, we first setup ->ops[type], then load quota inode, and only after
that enable flags which sb_has_quota_active() is checking so I don't see a
need for additional checking of dqopt->ops[qid->type].

> Also, I notice you have this queued on the for_next branch and not the
> for_linus branch.  I was hoping you could push this to Linus sooner
> than the next merge cycle, since this is (a) making my testing hard,
> and (b) it makes it easy for an attacker to crash the system.  For
> similar reasons, perhaps this should have a cc: stable@...r.kernel.org
> tag?

The problematic code was merged in this merge window so no point to cc
stable. I want to push the fix to Linus for rc3 (likely today or tomorrow)
so you should be able to get that soon. Sorry for complications.

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