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authorElena Reshetova <elena.reshetova@intel.com>2017-10-20 06:26:01 -0400
committerJan Kara <jack@suse.cz>2017-10-31 12:54:56 -0400
commit7761daa6a1599fa5479b8da367470f632a1927e0 (patch)
treef1ed23c310e76b1a78447268f9d16c153bb32721
parent9cf90cef362d44b2f3fcdb7d0694849a6308b620 (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.c6
-rw-r--r--include/linux/fsnotify_backend.h3
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)
107 */ 107 */
108void fsnotify_get_group(struct fsnotify_group *group) 108void fsnotify_get_group(struct fsnotify_group *group)
109{ 109{
110 atomic_inc(&group->refcnt); 110 refcount_inc(&group->refcnt);
111} 111}
112 112
113/* 113/*
@@ -115,7 +115,7 @@ void fsnotify_get_group(struct fsnotify_group *group)
115 */ 115 */
116void fsnotify_put_group(struct fsnotify_group *group) 116void fsnotify_put_group(struct fsnotify_group *group)
117{ 117{
118 if (atomic_dec_and_test(&group->refcnt)) 118 if (refcount_dec_and_test(&group->refcnt))
119 fsnotify_final_destroy_group(group); 119 fsnotify_final_destroy_group(group);
120} 120}
121 121
@@ -131,7 +131,7 @@ struct fsnotify_group *fsnotify_alloc_group(const struct fsnotify_ops *ops)
131 return ERR_PTR(-ENOMEM); 131 return ERR_PTR(-ENOMEM);
132 132
133 /* set to 0 when there a no external references to this group */ 133 /* set to 0 when there a no external references to this group */
134 atomic_set(&group->refcnt, 1); 134 refcount_set(&group->refcnt, 1);
135 atomic_set(&group->num_marks, 0); 135 atomic_set(&group->num_marks, 0);
136 atomic_set(&group->user_waits, 0); 136 atomic_set(&group->user_waits, 0);
137 137
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 @@
17#include <linux/types.h> 17#include <linux/types.h>
18#include <linux/atomic.h> 18#include <linux/atomic.h>
19#include <linux/user_namespace.h> 19#include <linux/user_namespace.h>
20#include <linux/refcount.h>
20 21
21/* 22/*
22 * IN_* from inotfy.h lines up EXACTLY with FS_*, this is so we can easily 23 * IN_* from inotfy.h lines up EXACTLY with FS_*, this is so we can easily
@@ -135,7 +136,7 @@ struct fsnotify_group {
135 * inotify_init() and the refcnt will hit 0 only when that fd has been 136 * inotify_init() and the refcnt will hit 0 only when that fd has been
136 * closed. 137 * closed.
137 */ 138 */
138 atomic_t refcnt; /* things with interest in this group */ 139 refcount_t refcnt; /* things with interest in this group */
139 140
140 const struct fsnotify_ops *ops; /* how this group handles things */ 141 const struct fsnotify_ops *ops; /* how this group handles things */
141 142