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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>
This commit is contained in:
Elena Reshetova 2017-10-20 13:26:02 +03:00 committed by Jan Kara
parent 6685df3125
commit ab97f87325
4 changed files with 11 additions and 11 deletions
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4
fs/notify/inotify/inotify_user.c
View File

@ -376,7 +376,7 @@ static struct inotify_inode_mark *inotify_idr_find_locked(struct fsnotify_group
fsnotify_get_mark(fsn_mark);
/* One ref for being in the idr, one ref we just took */
BUG_ON(atomic_read(&fsn_mark->refcnt) < 2);
BUG_ON(refcount_read(&fsn_mark->refcnt) < 2);
}
return i_mark;
@ -446,7 +446,7 @@ static void inotify_remove_from_idr(struct fsnotify_group *group,
* One ref for being in the idr
* one ref grabbed by inotify_idr_find
*/
if (unlikely(atomic_read(&i_mark->fsn_mark.refcnt) < 2)) {
if (unlikely(refcount_read(&i_mark->fsn_mark.refcnt) < 2)) {
printk(KERN_ERR "%s: i_mark=%p i_mark->wd=%d i_mark->group=%p\n",
__func__, i_mark, i_mark->wd, i_mark->fsn_mark.group);
/* we can't really recover with bad ref cnting.. */

14
fs/notify/mark.c
View File

@ -105,8 +105,8 @@ static DECLARE_WORK(connector_reaper_work, fsnotify_connector_destroy_workfn);
void fsnotify_get_mark(struct fsnotify_mark *mark)
{
WARN_ON_ONCE(!atomic_read(&mark->refcnt));
atomic_inc(&mark->refcnt);
WARN_ON_ONCE(!refcount_read(&mark->refcnt));
refcount_inc(&mark->refcnt);
}
static void __fsnotify_recalc_mask(struct fsnotify_mark_connector *conn)
@ -201,7 +201,7 @@ void fsnotify_put_mark(struct fsnotify_mark *mark)
/* Catch marks that were actually never attached to object */
if (!mark->connector) {
if (atomic_dec_and_test(&mark->refcnt))
if (refcount_dec_and_test(&mark->refcnt))
fsnotify_final_mark_destroy(mark);
return;
}
@ -210,7 +210,7 @@ void fsnotify_put_mark(struct fsnotify_mark *mark)
* We have to be careful so that traversals of obj_list under lock can
* safely grab mark reference.
*/
if (!atomic_dec_and_lock(&mark->refcnt, &mark->connector->lock))
if (!refcount_dec_and_lock(&mark->refcnt, &mark->connector->lock))
return;
conn = mark->connector;
@ -258,7 +258,7 @@ static bool fsnotify_get_mark_safe(struct fsnotify_mark *mark)
if (!mark)
return true;
if (atomic_inc_not_zero(&mark->refcnt)) {
if (refcount_inc_not_zero(&mark->refcnt)) {
spin_lock(&mark->lock);
if (mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED) {
/* mark is attached, group is still alive then */
@ -335,7 +335,7 @@ void fsnotify_detach_mark(struct fsnotify_mark *mark)
WARN_ON_ONCE(!mutex_is_locked(&group->mark_mutex));
WARN_ON_ONCE(!srcu_read_lock_held(&fsnotify_mark_srcu) &&
atomic_read(&mark->refcnt) < 1 +
refcount_read(&mark->refcnt) < 1 +
!!(mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED));
spin_lock(&mark->lock);
@ -737,7 +737,7 @@ void fsnotify_init_mark(struct fsnotify_mark *mark,
{
memset(mark, 0, sizeof(*mark));
spin_lock_init(&mark->lock);
atomic_set(&mark->refcnt, 1);
refcount_set(&mark->refcnt, 1);
fsnotify_get_group(group);
mark->group = group;
}

2
include/linux/fsnotify_backend.h
View File

@ -242,7 +242,7 @@ struct fsnotify_mark {
__u32 mask;
/* We hold one for presence in g_list. Also one ref for each 'thing'
* in kernel that found and may be using this mark. */
atomic_t refcnt;
refcount_t refcnt;
/* Group this mark is for. Set on mark creation, stable until last ref
* is dropped */
struct fsnotify_group *group;

2
kernel/audit_tree.c
View File

@ -1007,7 +1007,7 @@ static void audit_tree_freeing_mark(struct fsnotify_mark *entry, struct fsnotify
* We are guaranteed to have at least one reference to the mark from
* either the inode or the caller of fsnotify_destroy_mark().
*/
BUG_ON(atomic_read(&entry->refcnt) < 1);
BUG_ON(refcount_read(&entry->refcnt) < 1);
}
static const struct fsnotify_ops audit_tree_ops = {