[PATCH 1/2] net: qrtr: ns: Limit the maximum server registration per node

[Manivannan Sadhasivam]

Current code does no bound checking on the number of servers added per
node. A malicious client can flood NEW_SERVER messages and exhaust memory.

Fix this issue by limiting the maximum number of server registrations to
256 per node. If the NEW_SERVER message is received for an old port, then
don't restrict it as it will get replaced.

Note that the limit of 256 is chosen based on the current platform
requirements. If requirement changes in the future, this limit can be
increased.

Cc: stable@xxxxxxxxxxxxxxx
Fixes: 0c2204a4ad71 ("net: qrtr: Migrate nameservice to kernel from userspace")
Reported-by: Yiming Qian <yimingqian591@xxxxxxxxx>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@xxxxxxxxxxxxxxxx>
---
 net/qrtr/ns.c | 24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/net/qrtr/ns.c b/net/qrtr/ns.c
index 3203b2220860..fb4e8a2d370d 100644
--- a/net/qrtr/ns.c
+++ b/net/qrtr/ns.c
@@ -67,8 +67,14 @@ struct qrtr_server {
 struct qrtr_node {
 	unsigned int id;
 	struct xarray servers;
+	u32 server_count;
 };
 
+/* Max server limit is chosen based on the current platform requirements. If the
+ * requirement changes in the future, this value can be increased.
+ */
+#define QRTR_NS_MAX_SERVERS 256
+
 static struct qrtr_node *node_get(unsigned int node_id)
 {
 	struct qrtr_node *node;
@@ -229,6 +235,17 @@ static struct qrtr_server *server_add(unsigned int service,
 	if (!service || !port)
 		return NULL;
 
+	node = node_get(node_id);
+	if (!node)
+		return NULL;
+
+	/* Make sure the new servers per port are capped at the maximum value */
+	old = xa_load(&node->servers, port);
+	if (!old && node->server_count >= QRTR_NS_MAX_SERVERS) {
+		pr_err_ratelimited("QRTR client node %u exceeds max server limit!\n", node_id);
+		return NULL;
+	}
+
 	srv = kzalloc_obj(*srv);
 	if (!srv)
 		return NULL;
@@ -238,10 +255,6 @@ static struct qrtr_server *server_add(unsigned int service,
 	srv->node = node_id;
 	srv->port = port;
 
-	node = node_get(node_id);
-	if (!node)
-		goto err;
-
 	/* Delete the old server on the same port */
 	old = xa_store(&node->servers, port, srv, GFP_KERNEL);
 	if (old) {
@@ -252,6 +265,8 @@ static struct qrtr_server *server_add(unsigned int service,
 		} else {
 			kfree(old);
 		}
+	} else {
+		node->server_count++;
 	}
 
 	trace_qrtr_ns_server_add(srv->service, srv->instance,
@@ -292,6 +307,7 @@ static int server_del(struct qrtr_node *node, unsigned int port, bool bcast)
 	}
 
 	kfree(srv);
+	node->server_count--;
 
 	return 0;
 }
-- 
2.51.0