diff options
| author | Elena Reshetova <elena.reshetova@intel.com> | 2017-10-20 13:26:01 +0300 |
|---|---|---|
| committer | Jan Kara <jack@suse.cz> | 2017-10-31 17:54:56 +0100 |
| commit | 7761daa6a1599fa5479b8da367470f632a1927e0 (patch) | |
| tree | f1ed23c310e76b1a78447268f9d16c153bb32721 | |
| parent | 9cf90cef362d44b2f3fcdb7d0694849a6308b620 (diff) | |
fsnotify: convert fsnotify_group.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_group.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>
| -rw-r--r-- | fs/notify/group.c | 6 | ||||
| -rw-r--r-- | include/linux/fsnotify_backend.h | 3 |
2 files changed, 5 insertions, 4 deletions
diff --git a/fs/notify/group.c b/fs/notify/group.c index 32357534de18..b7a4b6a69efa 100644 --- a/fs/notify/group.c +++ b/fs/notify/group.c @@ -107,7 +107,7 @@ void fsnotify_destroy_group(struct fsnotify_group *group) */ void fsnotify_get_group(struct fsnotify_group *group) { - atomic_inc(&group->refcnt); + refcount_inc(&group->refcnt); } /* @@ -115,7 +115,7 @@ void fsnotify_get_group(struct fsnotify_group *group) */ void fsnotify_put_group(struct fsnotify_group *group) { - if (atomic_dec_and_test(&group->refcnt)) + if (refcount_dec_and_test(&group->refcnt)) fsnotify_final_destroy_group(group); } @@ -131,7 +131,7 @@ struct fsnotify_group *fsnotify_alloc_group(const struct fsnotify_ops *ops) return ERR_PTR(-ENOMEM); /* set to 0 when there a no external references to this group */ - atomic_set(&group->refcnt, 1); + refcount_set(&group->refcnt, 1); atomic_set(&group->num_marks, 0); atomic_set(&group->user_waits, 0); diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h index c6c69318752b..20a57bac38f2 100644 --- a/include/linux/fsnotify_backend.h +++ b/include/linux/fsnotify_backend.h @@ -17,6 +17,7 @@ #include <linux/types.h> #include <linux/atomic.h> #include <linux/user_namespace.h> +#include <linux/refcount.h> /* * IN_* from inotfy.h lines up EXACTLY with FS_*, this is so we can easily @@ -135,7 +136,7 @@ struct fsnotify_group { * inotify_init() and the refcnt will hit 0 only when that fd has been * closed. */ - atomic_t refcnt; /* things with interest in this group */ + refcount_t refcnt; /* things with interest in this group */ const struct fsnotify_ops *ops; /* how this group handles things */ |