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Date:   Mon, 20 Feb 2017 13:29:48 +0200
From:   Elena Reshetova <elena.reshetova@...el.com>
To:     linux-kernel@...r.kernel.org
Cc:     peterz@...radead.org, gregkh@...uxfoundation.org,
        akpm@...ux-foundation.org, ebiederm@...ssion.com, mingo@...hat.com,
        adobriyan@...il.com, serge@...lyn.com, arozansk@...hat.com,
        dave@...olabs.net, Elena Reshetova <elena.reshetova@...el.com>,
        Hans Liljestrand <ishkamiel@...il.com>,
        Kees Cook <keescook@...omium.org>,
        David Windsor <dwindsor@...il.com>
Subject: [PATCH 2/3] ipc: convert sem_undo_list.refcnt from atomic_t to refcount_t

refcount_t type and corresponding API should be
used instead of atomic_t when the variable is used as
a reference counter. This allows to avoid accidental
refcounter overflows that might lead to use-after-free
situations.

Signed-off-by: Elena Reshetova <elena.reshetova@...el.com>
Signed-off-by: Hans Liljestrand <ishkamiel@...il.com>
Signed-off-by: Kees Cook <keescook@...omium.org>
Signed-off-by: David Windsor <dwindsor@...il.com>
---
 ipc/sem.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/ipc/sem.c b/ipc/sem.c
index e468cd1..9063ffa 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -139,7 +139,7 @@ struct sem_undo {
  * that may be shared among all a CLONE_SYSVSEM task group.
  */
 struct sem_undo_list {
-	atomic_t		refcnt;
+	refcount_t		refcnt;
 	spinlock_t		lock;
 	struct list_head	list_proc;
 };
@@ -1646,7 +1646,7 @@ static inline int get_undo_list(struct sem_undo_list **undo_listp)
 		if (undo_list == NULL)
 			return -ENOMEM;
 		spin_lock_init(&undo_list->lock);
-		atomic_set(&undo_list->refcnt, 1);
+		refcount_set(&undo_list->refcnt, 1);
 		INIT_LIST_HEAD(&undo_list->list_proc);
 
 		current->sysvsem.undo_list = undo_list;
@@ -2045,7 +2045,7 @@ int copy_semundo(unsigned long clone_flags, struct task_struct *tsk)
 		error = get_undo_list(&undo_list);
 		if (error)
 			return error;
-		atomic_inc(&undo_list->refcnt);
+		refcount_inc(&undo_list->refcnt);
 		tsk->sysvsem.undo_list = undo_list;
 	} else
 		tsk->sysvsem.undo_list = NULL;
@@ -2074,7 +2074,7 @@ void exit_sem(struct task_struct *tsk)
 		return;
 	tsk->sysvsem.undo_list = NULL;
 
-	if (!atomic_dec_and_test(&ulp->refcnt))
+	if (!refcount_dec_and_test(&ulp->refcnt))
 		return;
 
 	for (;;) {
-- 
2.7.4

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