[PATCH 3/3] ipc: convert kern_ipc_perm.refcount from atomic_t to refcount_t

[Elena Reshetova]

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@xxxxxxxxx>
Signed-off-by: Hans Liljestrand <ishkamiel@xxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: David Windsor <dwindsor@xxxxxxxxx>
---
 include/linux/ipc.h | 3 ++-
 ipc/util.c          | 6 +++---
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/include/linux/ipc.h b/include/linux/ipc.h
index fadd579..ae68980 100644
--- a/include/linux/ipc.h
+++ b/include/linux/ipc.h
@@ -4,6 +4,7 @@
 #include <linux/spinlock.h>
 #include <linux/uidgid.h>
 #include <uapi/linux/ipc.h>
+#include <linux/refcount.h>
 
 #define IPCMNI 32768  /* <= MAX_INT limit for ipc arrays (including sysctl changes) */
 
@@ -22,7 +23,7 @@ struct kern_ipc_perm {
 	void		*security;
 
 	struct rcu_head rcu;
-	atomic_t refcount;
+	refcount_t refcount;
 } ____cacheline_aligned_in_smp __randomize_layout;
 
 #endif /* _LINUX_IPC_H */
diff --git a/ipc/util.c b/ipc/util.c
index 1a2cb02..069bb22 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -232,7 +232,7 @@ int ipc_addid(struct ipc_ids *ids, struct kern_ipc_perm *new, int size)
 
 	idr_preload(GFP_KERNEL);
 
-	atomic_set(&new->refcount, 1);
+	refcount_set(&new->refcount, 1);
 	spin_lock_init(&new->lock);
 	new->deleted = false;
 	rcu_read_lock();
@@ -397,13 +397,13 @@ void ipc_rmid(struct ipc_ids *ids, struct kern_ipc_perm *ipcp)
 
 int ipc_rcu_getref(struct kern_ipc_perm *ptr)
 {
-	return atomic_inc_not_zero(&ptr->refcount);
+	return refcount_inc_not_zero(&ptr->refcount);
 }
 
 void ipc_rcu_putref(struct kern_ipc_perm *ptr,
 			void (*func)(struct rcu_head *head))
 {
-	if (!atomic_dec_and_test(&ptr->refcount))
+	if (!refcount_dec_and_test(&ptr->refcount))
 		return;
 
 	call_rcu(&ptr->rcu, func);
-- 
2.7.4