Re: [PATCH v3 2/4] xfs: initialize inode security on tmpfile creation

[Stephen Smalley <sds@xxxxxxxxxxxxx>]

On 04/16/2014 10:14 AM, Christoph Hellwig wrote:
> On Wed, Apr 16, 2014 at 08:51:38AM -0400, Stephen Smalley wrote:
>> Maybe I spoke too soon.  IIUC, I_LINKABLE doesn't necessarily
>> distinguish tmpfiles from other files, as some tmpfiles may be linkable
>> and others not.  But what we want is a way to identify all tmpfiles when
>> security_inode_init_security() is called if we are going to label them
>> independently of the provided dir.
> 
> Oh, right.  If O_EXCL is specified (another annoying overload of the
> flag..) the tmpfile can't ever be linked back into the filesystem
> and thus doesn't have I_LINKABLE set.
> 
> I guess the best way to fix this is using the magic qstr you suggested
> before.  That means security_inode_init_security would need to be
> called after d_tmpfile, which most filesystems don't do right now.

I think one could just pass NULL for the qstr as an indicator, which
ext4 already does, so it doesn't require moving after d_tmpfile) IIUC.
However, that doesn't solve the problem for security_inode_create(),
which also needs to know it is dealing with a tmpfile.  So we might want
to just pass an explicit flag to both.