statx: Kill fd-with-NULL-path support in favour of AT_EMPTY_PATH

With the new statx() syscall, the following both allow the attributes of
the file attached to a file descriptor to be retrieved:

	statx(dfd, NULL, 0, ...);

and:

	statx(dfd, "", AT_EMPTY_PATH, ...);

Change the code to reject the first option, though this means copying
the path and engaging pathwalk for the fstat() equivalent.  dfd can be a
non-directory provided path is "".

[ The timing of this isn't wonderful, but applying this now before we
  have statx() in any released kernel, before anybody starts using the
  NULL special case.    - Linus ]

Fixes: a528d35e8bfc ("statx: Add a system call to make enhanced file info available")
Reported-by: Michael Kerrisk <[email protected]>
Signed-off-by: David Howells <[email protected]>
cc: Eric Sandeen <[email protected]>
cc: [email protected]
cc: [email protected]
cc: [email protected]
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions