[RFC PATCH 0/1] xattr: Allow user.* xattr on symlink/special files if caller has CAP_SYS_RESOURCE

[Vivek Goyal]

On Wed, Jun 30, 2021 at 03:59:41PM -0400, Theodore Ts'o wrote:
> On Wed, Jun 30, 2021 at 04:01:42PM +0100, Dr. David Alan Gilbert wrote:
> > 
> > Even if you fix symlinks, I don't think it fixes device nodes or
> > anything else where the permissions bitmap isn't purely used as the
> > permissions on the inode.
> 
> I think we're making a mountain out of a molehill.  Again, very few
> people are using quota these days.  And if you give someone write
> access to a 8TB disk, do you really care if they can "steal" 32k worth
> of space (which is the maximum size of an xattr, enforced by the VFS).

So that should be N * 32K per inode, where N is number of user xattrs
one can write on the inode. (user.1, user.2, user.3, .., user.N)?

Vivek

> 
> OK, but what about character mode devices?  First of all, most users
> don't have access to huge number of devices, but let's assume
> something absurd.  Let's say that a user has write access to *1024*
> devices.  (My /dev has 233 character mode devices, and I have write
> access to well under a dozen.)
> 
> An 8TB disk costs about $200.  So how much of the "stolen" quota space
> are we talking about, assuming the user has access to 1024 devices,
> and the file system actually supports a 32k xattr.
> 
>     32k * 1024 * $200 / 8TB / (1024*1024*1024) = $0.000763 = 0.0763 cents
> 
> A 2TB SSD is less around $180, so even if we calculate the prices
> based on SSD space, we're still talking about a quarter of a penny.
> 
> Why are we worrying about this?
> 
> 						- Ted
>