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>

1 files changed, 1 insertions, 1 deletions

diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
index c259271c35a4..2ed368a91a10 100644
--- a/fs/nfsd/state.h
+++ b/fs/nfsd/state.h
@@ -468,7 +468,7 @@ struct nfs4_clnt_odstate {
 	struct nfs4_client	*co_client;
 	struct nfs4_file	*co_file;
 	struct list_head	co_perfile;
-	atomic_t		co_odcount;
+	refcount_t		co_odcount;
 };
 
 /*