iscsi target: fix session creation failure handling

The problem is that iscsi_login_zero_tsih_s1 sets conn->sess early in
iscsi_login_set_conn_values. If the function fails later like when we
alloc the idr it does kfree(sess) and leaves the conn->sess pointer set.
iscsi_login_zero_tsih_s1 then returns -Exyz and we then call
iscsi_target_login_sess_out and access the freed memory.

This patch has iscsi_login_zero_tsih_s1 either completely setup the
session or completely tear it down, so later in
iscsi_target_login_sess_out we can just check for it being set to the
connection.

Cc: stable@vger.kernel.org
Fixes: 0957627a9960 ("iscsi-target: Fix sess allocation leak in...")
Signed-off-by: Mike Christie <mchristi@redhat.com>
Acked-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Matthew Wilcox <willy@infradead.org>

drivers/target/iscsi/iscsi_target_login.c

@@ -348,8 +348,7 @@ static int iscsi_login_zero_tsih_s1(
 		pr_err("idr_alloc() for sess_idr failed\n");
 		iscsit_tx_login_rsp(conn, ISCSI_STATUS_CLS_TARGET_ERR,
 				ISCSI_LOGIN_STATUS_NO_RESOURCES);
-		kfree(sess);
-		return -ENOMEM;
+		goto free_sess;
 	}
 
 	sess->creation_time = get_jiffies_64();
@@ -365,20 +364,28 @@ static int iscsi_login_zero_tsih_s1(
 				ISCSI_LOGIN_STATUS_NO_RESOURCES);
 		pr_err("Unable to allocate memory for"
 				" struct iscsi_sess_ops.\n");
-		kfree(sess);
-		return -ENOMEM;
+		goto remove_idr;
 	}
 
 	sess->se_sess = transport_init_session(TARGET_PROT_NORMAL);
 	if (IS_ERR(sess->se_sess)) {
 		iscsit_tx_login_rsp(conn, ISCSI_STATUS_CLS_TARGET_ERR,
 				ISCSI_LOGIN_STATUS_NO_RESOURCES);
-		kfree(sess->sess_ops);
-		kfree(sess);
-		return -ENOMEM;
+		goto free_ops;
 	}
 
 	return 0;
+
+free_ops:
+	kfree(sess->sess_ops);
+remove_idr:
+	spin_lock_bh(&sess_idr_lock);
+	idr_remove(&sess_idr, sess->session_index);
+	spin_unlock_bh(&sess_idr_lock);
+free_sess:
+	kfree(sess);
+	conn->sess = NULL;
+	return -ENOMEM;
 }
 
 static int iscsi_login_zero_tsih_s2(
@@ -1161,13 +1168,13 @@ void iscsi_target_login_sess_out(struct iscsi_conn *conn,
 				   ISCSI_LOGIN_STATUS_INIT_ERR);
 	if (!zero_tsih || !conn->sess)
 		goto old_sess_out;
-	if (conn->sess->se_sess)
-		transport_free_session(conn->sess->se_sess);
-	if (conn->sess->session_index != 0) {
-		spin_lock_bh(&sess_idr_lock);
-		idr_remove(&sess_idr, conn->sess->session_index);
-		spin_unlock_bh(&sess_idr_lock);
-	}
+
+	transport_free_session(conn->sess->se_sess);
+
+	spin_lock_bh(&sess_idr_lock);
+	idr_remove(&sess_idr, conn->sess->session_index);
+	spin_unlock_bh(&sess_idr_lock);
+
 	kfree(conn->sess->sess_ops);
 	kfree(conn->sess);
 	conn->sess = NULL;