linux-kernel - Re: [PATCH -V6 09/26] vfs: Add delete child and delete self permission flags

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Date:	Fri, 09 Sep 2011 10:49:19 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	"J. Bruce Fields" <bfields@...ldses.org>
Cc:	agruen@...nel.org, akpm@...ux-foundation.org, dhowells@...hat.com,
	linux-fsdevel@...r.kernel.org, linux-nfs@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -V6 09/26] vfs: Add delete child and delete self permission flags

On Thu, 8 Sep 2011 18:02:46 -0400, "J. Bruce Fields" <bfields@...ldses.org> wrote:
> On Thu, Sep 08, 2011 at 04:07:54PM -0400, J. Bruce Fields wrote:
> > On Thu, Sep 08, 2011 at 03:00:58PM +0530, Aneesh Kumar K.V wrote:
> > > On Wed, 7 Sep 2011 16:39:16 -0400, "J. Bruce Fields" <bfields@...ldses.org> wrote:
> > > > On Mon, Sep 05, 2011 at 10:55:31PM +0530, Aneesh Kumar K.V wrote:
> > > > > +static int may_delete(struct inode *dir, struct dentry *victim,
> > > > > +		      int isdir, int replace)
> > > > >  {
> > > > > -	int error;
> > > > > +	int mask, error, is_sticky;
> > > > > +	struct inode *inode = victim->d_inode;
> > > > >  
> > > > > -	if (!victim->d_inode)
> > > > > +	if (!inode)
> > > > >  		return -ENOENT;
> > > > >  
> > > > >  	BUG_ON(victim->d_parent->d_inode != dir);
> > > > >  	audit_inode_child(victim, dir);
> > > > >  
> > > > > -	error = inode_permission(dir, MAY_WRITE | MAY_EXEC);
> > > > > +	mask = MAY_WRITE | MAY_EXEC | MAY_DELETE_CHILD;
> > > > > +	if (replace)
> > > > > +		mask |= S_ISDIR(inode->i_mode) ?
> > > > > +			MAY_CREATE_DIR : MAY_CREATE_FILE;
> > > > 
> > > > I'm having trouble understanding this next bit:
> > > > 
> > > > > +	is_sticky = check_sticky(dir, inode);
> > > > > +	error = inode_permission(dir, mask);
> > > > > +	if ((error || is_sticky) && IS_RICHACL(inode) &&
> > > > > +	    !inode_permission(dir, mask & ~(MAY_WRITE | MAY_DELETE_CHILD)) &&
> > > > > +	    !inode_permission(inode, MAY_DELETE_SELF))
> > > > > +		error = 0;
> > > > 
> > > > OK, so we can ignore the lack of write or delete permissions on the
> > > > parent if we have delete_self permissions on the child.  I guess that's
> > > > right.
> > > > 
> > > > Why the "|| is_sticky" above?
> > > > 
> > > > Is there some less complicated why to write this?
> > > 
> > > we removed the ns_capable check out of check_sticky, because we don't
> > > want to do capability check when richacl allows access. We also want to
> > > make sure that even if mode bits allow access (inode_permission(dir, mask))
> > > if sticky bit is set we do additional check.
> > 
> > Why are the two inode_permissions ANDed?  The windows semantics are that
> > you can delete if you have MAY_DELETE_CHILD *or* MAY_DELETE_SELF.
> 
> Either way, those conditions are just really hard to follow.  Could you
> simplify the logic, add comments, maybe move the richacl stuff into a
> little helper function?
> 
> Also, a nit:
> 
> > > > > +	    !inode_permission(dir, mask & ~(MAY_WRITE | MAY_DELETE_CHILD)) &&
> 
> The way you calculated mask above it always includes MAY_WRITE and
> MAY_DELETE_CHILD, so the above is equivalent to just
> 
> 		    !inode_permission(dir, MAY_WRITE | MAY_DELETE_CHILD) &&
> 
> isn't it?
> 

I guess i can simplify it as 
  !inode_permission(dir, MAY_EXEC | replace_mask)
  
-aneesh
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