Re: [RFC] add FIEMAP ioctl to efficiently map file allocation

On 1 May 2007, at 05:22, David Chinner wrote:

On Mon, Apr 30, 2007 at 04:44:01PM -0600, Andreas Dilger wrote:

quoted

  The FIBMAP ioctl is for privileged users
  only, and I wonder if FIEMAP should be the same, or at least  
disallow
  mapping files that the user can't access especially with  
FLAG_SYNC and/or
  FLAG_HSM_READ.

I see little reason for restricting FI[BE]MAP to privileged users -
anyone should be able to determine if files they have permission to
access are fragmented.

Allowing anyone to run FI[BE]MAP creates potential for DOS-ing the  
machine.  Perhaps for non-privileged users FIEMAP has to be read- 
only?  As soon as any of the FLAG_* flags come into play you make it  
privileged.  For example fancy any user being able to fill up your  
file system by calling FIEMAP with FLAG_HSM_READ on all files  
recursively?  This should certainly not be simply dismissed as a non- 
issue without thinking about it first...

Best regards,

	Anton
-- 
Anton Altaparmakov <aia21 at cam.ac.uk> (replace at with @)
Unix Support, Computing Service, University of Cambridge, CB2 3QH, UK
Linux NTFS maintainer, http://www.linux-ntfs.org/