fs, nilfs: convert nilfs_root.count from atomic_t to refcount_t
authorElena Reshetova <elena.reshetova@intel.com>
Fri, 17 Nov 2017 23:29:39 +0000 (15:29 -0800)
committerLinus Torvalds <torvalds@linux-foundation.org>
Sat, 18 Nov 2017 00:10:03 +0000 (16:10 -0800)
commitd4f0284a5969fd7809ec8df710eb10598b701638
treea38d9b3bbf2722d859a374dbe2cf06a97fa13273
parent31ccb1f7ba3cfe29631587d451cf5bb8ab593550
fs, nilfs: convert nilfs_root.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 nilfs_root.count is used as pure reference counter.
Convert it to refcount_t and fix up the operations.

Link: http://lkml.kernel.org/r/1509367935-3086-3-git-send-email-konishi.ryusuke@lab.ntt.co.jp
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Suggested-by: Kees Cook <keescook@chromium.org>
Reviewed-by: David Windsor <dwindsor@gmail.com>
Reviewed-by: Hans Liljestrand <ishkamiel@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
fs/nilfs2/the_nilfs.c
fs/nilfs2/the_nilfs.h