linux-ext4 - Re: [PATCH] ext4: fix NULL pointer dereference in ext4_quota

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Date:	Mon, 16 May 2011 13:03:08 +0200
From:	Jan Kara <jack@...e.cz>
To:	Lukas Czerner <lczerner@...hat.com>
Cc:	Jan Kara <jack@...e.cz>, Amir Goldstein <amir73il@...il.com>,
	Ext4 Developers List <linux-ext4@...r.kernel.org>,
	Theodore Tso <tytso@....edu>
Subject: Re: [PATCH] ext4: fix NULL pointer dereference in ext4_quota_off

On Mon 16-05-11 12:53:47, Lukas Czerner wrote:
> On Mon, 16 May 2011, Jan Kara wrote:
> 
> > On Mon 16-05-11 11:49:22, Lukas Czerner wrote:
> > > On Mon, 16 May 2011, Amir Goldstein wrote:
> > > > diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> > > > index fc827bb..2689351 100644
> > > > --- a/fs/ext4/super.c
> > > > +++ b/fs/ext4/super.c
> > > > @@ -4681,6 +4681,9 @@ static int ext4_quota_off(struct super_block
> > > > *sb, int type)
> > > >  	if (test_opt(sb, DELALLOC))
> > > >  		sync_filesystem(sb);
> > > > 
> > > > +	if (!inode)
> > > > +		goto out;
> > > 
> > > Just out of curiosity, why would the quota inode be NULL ?
> >   Because quota is already turned off (we then release all references to
> > quota file). Just what I don't understand is why in Amir's testing quota is
> > not turned on before calling quota off. Because when I run the same test, I
> > don't trigger the issue.
> > 
> > 								Honza
> > 
> 
> Exactly, I did not read the quota code very deeply, but it seems to me
> that when we are turning the quota off, it should be on before. So if it
> is not, it might be something broken and this is not the solution (or
> maybe it is and I just do not see why:)).
  Well, userspace can try to turn quotas off whenever it desires and it
should not crash the kernel. The check whether quotas are actually turned
on is only in dquot_quota_off() called from ext4_quota_off(). It seems to
be some problem in Amir's build of xfstests that they happen to call
quotaoff on the fs is without quotas turned on. But anyway it should not
crash the kernel...

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