fs, nfs: convert pnfs_layout_hdr.plh_refcount from atomic_t to refcount_t
authorElena Reshetova <elena.reshetova@intel.com>
Fri, 20 Oct 2017 09:53:33 +0000 (12:53 +0300)
committerAnna Schumaker <Anna.Schumaker@Netapp.com>
Fri, 17 Nov 2017 18:47:59 +0000 (13:47 -0500)
commit2b28a7bee4539d27f4ec3b0298f03bfd83d4f794
treeeae9a1b4816de726573ee4367dc47c9a36a1d6a3
parenteba6dd691743a9d7a57735f36bf6946fc58878ec
fs, nfs: convert pnfs_layout_hdr.plh_refcount from atomic_t to refcount_t

atomic_t variables are currently used to implement reference
counters with the following properties:
 - counter is initialized to 1 using atomic_set()
 - a resource is freed upon counter reaching zero
 - once counter reaches zero, its further
   increments aren't allowed
 - counter schema uses basic atomic operations
   (set, inc, inc_not_zero, dec_and_test, etc.)

Such atomic variables should be converted to a newly provided
refcount_t type and API that prevents accidental counter overflows
and underflows. This is important since overflows and underflows
can lead to use-after-free situation and be exploitable.

The variable pnfs_layout_hdr.plh_refcount is used as pure reference counter.
Convert it to refcount_t and fix up the operations.

Suggested-by: Kees Cook <keescook@chromium.org>
Reviewed-by: David Windsor <dwindsor@gmail.com>
Reviewed-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
fs/nfs/pnfs.c
fs/nfs/pnfs.h