[PATCH BlueZ] audio/avrcp: Fix crash with invalid UTF-8 item name

["Frédéric Danis" <frederic.danis@collabora.com>]

As stated in AVRCP 1.6.2 chapter 6.10.2.3 Media element item, for the
Displayable Name Length property, the target device may truncate the
item name:

  Length of Displayable Name in octets. The name shall be limited such
  that a response to a GetFolderItems containing one media player item
  fits within the maximum size of PDU which can be received by the CT.

This truncatation may occur in the middle of a multi-byte character,
at least with Samsung Music app, which triggers a DBus assertion and
crashes bluetoothd:

  profiles/audio/player.c:media_folder_create_item() Din Dhal Jaye
      Haye with lyrics | "दिन ढल जाए
      हाय" गाने के बो� type audio uid 1
  profiles/audio/player.c:media_folder_create_item()
      /org/bluez/hci0/dev_24_24_B7_11_82_6C/player0/NowPlaying/item1
  profiles/audio/player.c:media_player_set_metadata() Title: Din Dhal
      Jaye Haye with lyrics | "दिन ढल जाए हाय"
      गाने के बोल | Guide | Dev Anand, Waheeda Rehman
  …
  arguments to dbus_message_iter_append_basic() were incorrect,
      assertion "_dbus_check_is_valid_utf8 (*string_p)" failed in
      file dbus-message.c line 2775.
  This is normally a bug in some application using the D-Bus library.
---
 profiles/audio/avrcp.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/profiles/audio/avrcp.c b/profiles/audio/avrcp.c
index 831f1dc8b..65b40c57f 100644
--- a/profiles/audio/avrcp.c
+++ b/profiles/audio/avrcp.c
@@ -2598,6 +2598,19 @@ static struct media_item *parse_media_element(struct avrcp *session,
 	if (namelen > 0)
 		memcpy(name, &operands[13], namelen);
 
+	/* Truncate name to the last valid UTF-8 character */
+	while (!g_utf8_validate(name, namelen, NULL)) {
+		char *end = g_utf8_find_prev_char(name, name + namelen);
+
+		if (end == NULL) {
+			name[0] = '\0';
+			break;
+		}
+
+		namelen = end - name;
+		name[namelen] = '\0';
+	}
+
 	count = operands[13 + namesize];
 
 	player = session->controller->player;
-- 
2.43.0