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

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

[Jan Kara]

On Fri 10-05-13 17:24:33, Cong Wang wrote:
> From: Cong Wang <amwang@redhat.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@suse.cz>
> Signed-off-by: Cong Wang <amwang@redhat.com>
  Good point. I've merged the patch.

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@suse.cz>
SUSE Labs, CR

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

[Jan Kara]

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@redhat.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@suse.cz>
> > Signed-off-by: Cong Wang <amwang@redhat.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@suse.cz>
> SUSE Labs, CR
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR

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

[Cong Wang]

On Mon, 2013-05-13 at 12:18 +0200, Jan Kara wrote:
> 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@redhat.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@suse.cz>
> > > Signed-off-by: Cong Wang <amwang@redhat.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.
> 

You are right. Thanks for looking into this!


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