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Re: [PATCH v10 10/11] quota: Add proper versioning support to fs_quota_s

To: Jan Kara <jack@xxxxxxx>
Subject: Re: [PATCH v10 10/11] quota: Add proper versioning support to fs_quota_stat
From: Ben Myers <bpm@xxxxxxx>
Date: Wed, 10 Jul 2013 13:47:04 -0500
Cc: Chandra Seetharaman <sekharan@xxxxxxxxxx>, xfs@xxxxxxxxxxx, swhiteho@xxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20130710162602.GB32444@xxxxxxxxxxxxx>
References: <1372371914-11370-1-git-send-email-sekharan@xxxxxxxxxx> <1372371914-11370-11-git-send-email-sekharan@xxxxxxxxxx> <20130710155538.GY20932@xxxxxxx> <20130710162602.GB32444@xxxxxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
Hey Jan,

On Wed, Jul 10, 2013 at 06:26:02PM +0200, Jan Kara wrote:
> On Wed 10-07-13 10:55:38, Ben Myers wrote:
> > Hey Chandra,
> > 
> > On Thu, Jun 27, 2013 at 05:25:13PM -0500, Chandra Seetharaman wrote:
> > > Added appropriate pads and code for backward compatibility.
> > > 
> > > Copied over the old version as it is different from the newer padded
> > > version.
> > > 
> > > New callers of the system call have to set the version of the data
> > > structure being passed, and kernel will fill as much data as requested.
> > > 
> > > Signed-off-by: Chandra Seetharaman <sekharan@xxxxxxxxxx>
> > 
> > I think we also need to
> > 
> > Cc: Jan Kara <jack@xxxxxxx>
>   Thanks for CC.
> 
> > > diff --git a/fs/gfs2/quota.c b/fs/gfs2/quota.c
> > > index c7c840e..ca0dccd 100644
> > > --- a/fs/gfs2/quota.c
> > > +++ b/fs/gfs2/quota.c
> > > @@ -1443,9 +1443,6 @@ static int gfs2_quota_get_xstate(struct super_block 
> > > *sb,
> > >  {
> > >   struct gfs2_sbd *sdp = sb->s_fs_info;
> > >  
> > > - memset(fqs, 0, sizeof(struct fs_quota_stat));
> > > - fqs->qs_version = FS_QSTAT_VERSION;
> > > -
> > >   switch (sdp->sd_args.ar_quota) {
> > >   case GFS2_QUOTA_ON:
> > >           fqs->qs_flags |= (FS_QUOTA_UDQ_ENFD | FS_QUOTA_GDQ_ENFD);
> > > diff --git a/fs/quota/quota.c b/fs/quota/quota.c
> > > index c7314f1..ae6526e 100644
> > > --- a/fs/quota/quota.c
> > > +++ b/fs/quota/quota.c
> > > @@ -207,12 +207,57 @@ static int quota_setxstate(struct super_block *sb, 
> > > int cmd, void __user *addr)
> > >  static int quota_getxstate(struct super_block *sb, void __user *addr)
> > >  {
> > >   struct fs_quota_stat fqs;
> > > - int ret;
> > > + struct fs_quota_stat_v1 fqs_v1;
> > > + int ret, size;
> > > + void *fqsp;
> > >  
> > >   if (!sb->s_qcop->get_xstate)
> > >           return -ENOSYS;
> > > +
> > > + memset(&fqs, 0, sizeof(struct fs_quota_stat));
> > > + if (copy_from_user(&fqs, addr, 1)) /* just get the version */
> > > +         return -EFAULT;
> > > +
> > > + switch (fqs.qs_version) {
> > > + case FS_QSTAT_VERSION_2:
> > > +         size = FS_QSTAT_V2_SIZE;
> > > +         break;
> > > + default:
> > > +         fqs.qs_version = FS_QSTAT_VERSION;
> > > +         /* fallthrough */
> > > + case FS_QSTAT_VERSION:
> > > +         size = FS_QSTAT_V1_SIZE;
> > > +         break;
> > > + }
>   Guys, you cannot really do this. If anyone is using getxstate() with
> uninitialized buffer (which is fine so far), you cannot suddently start to
> rely on the contents of qs_version field. That's ABI (and even API)
> breakage.

Looks like you are correct to me.  Seems that qs_version number was never
checked until this patch.

> Unless I'm missing something, the only clean way is to use new quotactl
> value for the interface with version field used for input as well.

If I understand... it would be something like this?

#define Q_XGETQSTATV     XQM_CMD(8)

Or Q_XGETQSTAT2?

Thanks,
        Ben

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