fsnotify: convert fsnotify_mark.refcnt from atomic_t to refcount_t
authorElena Reshetova <elena.reshetova@intel.com>
Fri, 20 Oct 2017 10:26:02 +0000 (13:26 +0300)
committerJan Kara <jack@suse.cz>
Tue, 31 Oct 2017 16:54:56 +0000 (17:54 +0100)
commitab97f87325e28b7ef7717e6cb62e8da14a7176e1
tree7ce8f0a747efaff1907f3774479dcbc2f4762c48
parent6685df31255493c3f0e9e0b8bf885e4c9762fc5d
fsnotify: convert fsnotify_mark.refcnt 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 fsnotify_mark.refcnt 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: Jan Kara <jack@suse.cz>
fs/notify/inotify/inotify_user.c
fs/notify/mark.c
include/linux/fsnotify_backend.h
kernel/audit_tree.c