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

[Elena Reshetova <elena.reshetova@intel.com>]

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

diff --git a/ipc/util.c b/ipc/util.c
index 798cad1..24484a6 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -437,7 +437,7 @@ void *ipc_rcu_alloc(int size)
 	struct ipc_rcu *out = ipc_alloc(sizeof(struct ipc_rcu) + size);
 	if (unlikely(!out))
 		return NULL;
-	atomic_set(&out->refcount, 1);
+	refcount_set(&out->refcount, 1);
 	return out + 1;
 }
 
@@ -445,14 +445,14 @@ int ipc_rcu_getref(void *ptr)
 {
 	struct ipc_rcu *p = ((struct ipc_rcu *)ptr) - 1;
 
-	return atomic_inc_not_zero(&p->refcount);
+	return refcount_inc_not_zero(&p->refcount);
 }
 
 void ipc_rcu_putref(void *ptr, void (*func)(struct rcu_head *head))
 {
 	struct ipc_rcu *p = ((struct ipc_rcu *)ptr) - 1;
 
-	if (!atomic_dec_and_test(&p->refcount))
+	if (!refcount_dec_and_test(&p->refcount))
 		return;
 
 	call_rcu(&p->rcu, func);
diff --git a/ipc/util.h b/ipc/util.h
index 51f7ca5..274ec9b 100644
--- a/ipc/util.h
+++ b/ipc/util.h
@@ -12,6 +12,7 @@
 
 #include <linux/unistd.h>
 #include <linux/err.h>
+#include <linux/refcount.h>
 
 #define SEQ_MULTIPLIER	(IPCMNI)
 
@@ -49,7 +50,7 @@ static inline void shm_exit_ns(struct ipc_namespace *ns) { }
 
 struct ipc_rcu {
 	struct rcu_head rcu;
-	atomic_t refcount;
+	refcount_t refcount;
 } ____cacheline_aligned_in_smp;
 
 #define ipc_rcu_to_struct(p)  ((void *)(p+1))
-- 
2.7.4