net, rds: convert rds_message.m_refcount 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@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>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/rds/message.c

@@ -48,8 +48,8 @@ static unsigned int	rds_exthdr_size[__RDS_EXTHDR_MAX] = {
 
 void rds_message_addref(struct rds_message *rm)
 {
-	rdsdebug("addref rm %p ref %d\n", rm, atomic_read(&rm->m_refcount));
-	atomic_inc(&rm->m_refcount);
+	rdsdebug("addref rm %p ref %d\n", rm, refcount_read(&rm->m_refcount));
+	refcount_inc(&rm->m_refcount);
 }
 EXPORT_SYMBOL_GPL(rds_message_addref);
 
@@ -83,9 +83,9 @@ static void rds_message_purge(struct rds_message *rm)
 
 void rds_message_put(struct rds_message *rm)
 {
-	rdsdebug("put rm %p ref %d\n", rm, atomic_read(&rm->m_refcount));
-	WARN(!atomic_read(&rm->m_refcount), "danger refcount zero on %p\n", rm);
-	if (atomic_dec_and_test(&rm->m_refcount)) {
+	rdsdebug("put rm %p ref %d\n", rm, refcount_read(&rm->m_refcount));
+	WARN(!refcount_read(&rm->m_refcount), "danger refcount zero on %p\n", rm);
+	if (refcount_dec_and_test(&rm->m_refcount)) {
 		BUG_ON(!list_empty(&rm->m_sock_item));
 		BUG_ON(!list_empty(&rm->m_conn_item));
 		rds_message_purge(rm);
@@ -206,7 +206,7 @@ struct rds_message *rds_message_alloc(unsigned int extra_len, gfp_t gfp)
 	rm->m_used_sgs = 0;
 	rm->m_total_sgs = extra_len / sizeof(struct scatterlist);
 
-	atomic_set(&rm->m_refcount, 1);
+	refcount_set(&rm->m_refcount, 1);
 	INIT_LIST_HEAD(&rm->m_sock_item);
 	INIT_LIST_HEAD(&rm->m_conn_item);
 	spin_lock_init(&rm->m_rs_lock);

net/rds/rds.h

@@ -356,7 +356,7 @@ static inline u32 rds_rdma_cookie_offset(rds_rdma_cookie_t cookie)
 #define RDS_MSG_FLUSH		8
 
 struct rds_message {
-	atomic_t		m_refcount;
+	refcount_t		m_refcount;
 	struct list_head	m_sock_item;
 	struct list_head	m_conn_item;
 	struct rds_incoming	m_inc;