fs, nfs: convert nfs_client.cl_count from atomic_t to refcount_t
authorElena Reshetova <elena.reshetova@intel.com>
Fri, 20 Oct 2017 09:53:38 +0000 (12:53 +0300)
committerAnna Schumaker <Anna.Schumaker@Netapp.com>
Fri, 17 Nov 2017 18:48:01 +0000 (13:48 -0500)
commit212bf41d88c06afc23e03f9b274eebf1e8dba197
tree755a58e9b423e6e8bfe06fa2036b633a427ff42b
parent2f62b5aa4814be2c511553fd6afb4d35b6c2503b
fs, nfs: convert nfs_client.cl_count 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 nfs_client.cl_count 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/client.c
fs/nfs/filelayout/filelayout.c
fs/nfs/flexfilelayout/flexfilelayout.c
fs/nfs/nfs4client.c
fs/nfs/nfs4proc.c
fs/nfs/nfs4state.c
include/linux/nfs_fs_sb.h