linux-kernel - Re: [Patch] quota: do not leak info to user-space

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Date:	Mon, 13 May 2013 12:18:39 +0200
From:	Jan Kara <jack@...e.cz>
To:	Cong Wang <amwang@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jan Kara <jack@...e.cz>, xfs@....sgi.com
Subject: Re: [Patch] quota: do not leak info to user-space

On Mon 13-05-13 12:04:23, Jan Kara wrote:
> On Fri 10-05-13 17:24:33, Cong Wang wrote:
> > From: Cong Wang <amwang@...hat.com>
> > 
> > There is a hole in struct fs_quota_stat, so we have to
> > zero the struct on stack before copying it to user-space.
> > 
> > Cc: Jan Kara <jack@...e.cz>
> > Signed-off-by: Cong Wang <amwang@...hat.com>
>   Good point. I've merged the patch.
  Ah, now I've noticed that XFS (the only user of the callback you are
fixing) is zeroing the structure on its own (xfs_qm_scall_getqstat). So
there's no real problem. I'm somewhat wondering whether clearing the field
in the place where you did it isn't more future-proof but usually we don't
pass in prezeroed buffers so I've decided to leave things as they are.

								Honza

> BTW for XFS folks: The structure definition looks somewhat odd (unaligned
> definition of qs_flags, qs_uquota starts only at 32-bit boundary although
> it has 64-bit fields in it) and I wouldn't be surprised if it needed compat
> wrapper for 32-bit apps on some architectures...
> 
> 								Honza
> > 
> > ---
> > diff --git a/fs/quota/quota.c b/fs/quota/quota.c
> > index c7314f1..2b0c182 100644
> > --- a/fs/quota/quota.c
> > +++ b/fs/quota/quota.c
> > @@ -211,6 +211,7 @@ static int quota_getxstate(struct super_block *sb, void __user *addr)
> >  
> >  	if (!sb->s_qcop->get_xstate)
> >  		return -ENOSYS;
> > +	memset(&fqs, 0, sizeof(fqs));
> >  	ret = sb->s_qcop->get_xstate(sb, &fqs);
> >  	if (!ret && copy_to_user(addr, &fqs, sizeof(fqs)))
> >  		return -EFAULT;
> -- 
> Jan Kara <jack@...e.cz>
> SUSE Labs, CR
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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