fs, nfsd: convert nfs4_cntl_odstate.co_odcount from atomic_t to refcount_t
authorElena Reshetova <elena.reshetova@intel.com>
Fri, 20 Oct 2017 09:53:29 +0000 (12:53 +0300)
committerJ. Bruce Fields <bfields@redhat.com>
Tue, 7 Nov 2017 21:43:59 +0000 (16:43 -0500)
commitcff7cb2ece397760195ff8a5fc6bf3c860810246
tree7d253b4fc7b44d2f1b2f0e9aa7715fad8479ae0e
parenta15dfcd529ab43265e70ec32d3b9d2286872d412
fs, nfsd: convert nfs4_cntl_odstate.co_odcount 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 nfs4_cntl_odstate.co_odcount 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: J. Bruce Fields <bfields@redhat.com>
fs/nfsd/nfs4state.c
fs/nfsd/state.h