From d514bc6d906ccbb3a8bd9afd2fc214f010c293c6 Mon Sep 17 00:00:00 2001
From: Fergus Dall <sidereal@google.com>
Date: Tue, 22 Jun 2021 19:31:26 +1000
Subject: [PATCH 2/2] connection: Handle non-nullable strings in
 wl_connection_demarshal

Currently a null string passed into a non-nullable argument of a message
will decode succesfully, probably resulting in the handler function
crashing. Instead treat it the same way we do non-nullable objects and ids.

Signed-off-by: Fergus Dall <sidereal@google.com>
---
 src/connection.c        |  7 +++++++
 tests/connection-test.c | 18 ++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/src/connection.c b/src/connection.c
index d0c7d9f..557c611 100644
--- a/src/connection.c
+++ b/src/connection.c
@@ -749,6 +749,13 @@ wl_connection_demarshal(struct wl_connection *connection,
 		case 's':
 			length = *p++;
 
+			if (length == 0 && !arg.nullable) {
+				wl_log("NULL string received on non-nullable "
+				       "type, message %s(%s)\n", message->name,
+				       message->signature);
+				errno = EINVAL;
+				goto err;
+			}
 			if (length == 0) {
 				closure->args[i].s = NULL;
 				break;
diff --git a/tests/connection-test.c b/tests/connection-test.c
index 669d73b..7220d87 100644
--- a/tests/connection-test.c
+++ b/tests/connection-test.c
@@ -553,6 +553,24 @@ expected_fail_demarshal(struct marshal_data *data, const char *format,
 	assert(errno == expected_error);
 }
 
+TEST(connection_demarshal_null_strings)
+{
+	struct marshal_data data;
+	uint32_t msg[3];
+
+	setup_marshal_data(&data);
+
+	data.value.s = NULL;
+	msg[0] = 400200;	/* object id */
+	msg[1] = 12 << 16;	/* size = 12, opcode = 0 */
+	msg[2] = 0;		/* string length = 0 */
+	demarshal(&data, "?s", msg, (void *) validate_demarshal_s);
+
+	expected_fail_demarshal(&data, "s", msg, EINVAL);
+
+	release_marshal_data(&data);
+}
+
 /* These tests are verifying that the demarshaling code will gracefully handle
  * clients lying about string and array lengths and giving values near
  * UINT32_MAX. Before fixes f7fdface and f5b9e3b9 this test would crash on
-- 
2.32.0.93.g670b81a890-goog