net, rds: convert rds_incoming.i_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/rds.h

@@ -8,6 +8,7 @@
 #include <linux/mutex.h>
 #include <linux/rds.h>
 #include <linux/rhashtable.h>
+#include <linux/refcount.h>
 
 #include "info.h"
 
@@ -261,7 +262,7 @@ struct rds_ext_header_rdma_dest {
 #define	RDS_MSG_RX_CMSG		3
 
 struct rds_incoming {
-	atomic_t		i_refcount;
+	refcount_t		i_refcount;
 	struct list_head	i_item;
 	struct rds_connection	*i_conn;
 	struct rds_conn_path	*i_conn_path;

net/rds/recv.c

@@ -45,7 +45,7 @@ void rds_inc_init(struct rds_incoming *inc, struct rds_connection *conn,
 {
 	int i;
 
-	atomic_set(&inc->i_refcount, 1);
+	refcount_set(&inc->i_refcount, 1);
 	INIT_LIST_HEAD(&inc->i_item);
 	inc->i_conn = conn;
 	inc->i_saddr = saddr;
@@ -61,7 +61,7 @@ EXPORT_SYMBOL_GPL(rds_inc_init);
 void rds_inc_path_init(struct rds_incoming *inc, struct rds_conn_path *cp,
 		       __be32 saddr)
 {
-	atomic_set(&inc->i_refcount, 1);
+	refcount_set(&inc->i_refcount, 1);
 	INIT_LIST_HEAD(&inc->i_item);
 	inc->i_conn = cp->cp_conn;
 	inc->i_conn_path = cp;
@@ -74,14 +74,14 @@ EXPORT_SYMBOL_GPL(rds_inc_path_init);
 
 static void rds_inc_addref(struct rds_incoming *inc)
 {
-	rdsdebug("addref inc %p ref %d\n", inc, atomic_read(&inc->i_refcount));
-	atomic_inc(&inc->i_refcount);
+	rdsdebug("addref inc %p ref %d\n", inc, refcount_read(&inc->i_refcount));
+	refcount_inc(&inc->i_refcount);
 }
 
 void rds_inc_put(struct rds_incoming *inc)
 {
-	rdsdebug("put inc %p ref %d\n", inc, atomic_read(&inc->i_refcount));
-	if (atomic_dec_and_test(&inc->i_refcount)) {
+	rdsdebug("put inc %p ref %d\n", inc, refcount_read(&inc->i_refcount));
+	if (refcount_dec_and_test(&inc->i_refcount)) {
 		BUG_ON(!list_empty(&inc->i_item));
 
 		inc->i_conn->c_trans->inc_free(inc);