net, rds: convert rds_mr.r_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/rdma.c

@@ -84,7 +84,7 @@ static struct rds_mr *rds_mr_tree_walk(struct rb_root *root, u64 key,
 	if (insert) {
 		rb_link_node(&insert->r_rb_node, parent, p);
 		rb_insert_color(&insert->r_rb_node, root);
-		atomic_inc(&insert->r_refcount);
+		refcount_inc(&insert->r_refcount);
 	}
 	return NULL;
 }
@@ -99,7 +99,7 @@ static void rds_destroy_mr(struct rds_mr *mr)
 	unsigned long flags;
 
 	rdsdebug("RDS: destroy mr key is %x refcnt %u\n",
-			mr->r_key, atomic_read(&mr->r_refcount));
+			mr->r_key, refcount_read(&mr->r_refcount));
 
 	if (test_and_set_bit(RDS_MR_DEAD, &mr->r_state))
 		return;
@@ -223,7 +223,7 @@ static int __rds_rdma_map(struct rds_sock *rs, struct rds_get_mr_args *args,
 		goto out;
 	}
 
-	atomic_set(&mr->r_refcount, 1);
+	refcount_set(&mr->r_refcount, 1);
 	RB_CLEAR_NODE(&mr->r_rb_node);
 	mr->r_trans = rs->rs_transport;
 	mr->r_sock = rs;
@@ -307,7 +307,7 @@ static int __rds_rdma_map(struct rds_sock *rs, struct rds_get_mr_args *args,
 
 	rdsdebug("RDS: get_mr key is %x\n", mr->r_key);
 	if (mr_ret) {
-		atomic_inc(&mr->r_refcount);
+		refcount_inc(&mr->r_refcount);
 		*mr_ret = mr;
 	}
 
@@ -756,7 +756,7 @@ int rds_cmsg_rdma_dest(struct rds_sock *rs, struct rds_message *rm,
 	if (!mr)
 		err = -EINVAL;	/* invalid r_key */
 	else
-		atomic_inc(&mr->r_refcount);
+		refcount_inc(&mr->r_refcount);
 	spin_unlock_irqrestore(&rs->rs_rdma_lock, flags);
 
 	if (mr) {

net/rds/rds.h

@@ -277,7 +277,7 @@ struct rds_incoming {
 
 struct rds_mr {
 	struct rb_node		r_rb_node;
-	atomic_t		r_refcount;
+	refcount_t		r_refcount;
 	u32			r_key;
 
 	/* A copy of the creation flags */
@@ -857,7 +857,7 @@ int rds_cmsg_atomic(struct rds_sock *rs, struct rds_message *rm,
 void __rds_put_mr_final(struct rds_mr *mr);
 static inline void rds_mr_put(struct rds_mr *mr)
 {
-	if (atomic_dec_and_test(&mr->r_refcount))
+	if (refcount_dec_and_test(&mr->r_refcount))
 		__rds_put_mr_final(mr);
 }