[PATCH BlueZ v2 08/10] device: Fix the name truncation splitting UTF-8 sequences

From: Luiz Augusto von Dentz <[email protected]>

btd_device_device_set_name() copies the name with

	strncpy(device->name, name, MAX_NAME_LENGTH);

which cuts at 248 bytes without any regard for where the UTF-8
characters start and end, so a longer name can be left with a partial
sequence. The result is no longer valid UTF-8 and D-Bus rejects it when
the Name property is emitted.

A name made of 249 U+FFFD characters is 747 bytes long and cutting it at
248 leaves a trailing "ef bf", two thirds of a character.

Truncate on a character boundary instead. The same name now ends up 246
bytes long and stays valid.

This also means a name that is not valid UTF-8 to begin with, as can be
had from the neard and sixaxis plugins, is now cut at the first
ill-formed sequence rather than passed on as is.

Assisted-by: Claude:claude-opus-5
---
 src/device.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/src/device.c b/src/device.c
index 65d84be56ca5..df607f718be1 100644
--- a/src/device.c
+++ b/src/device.c
@@ -5103,12 +5103,22 @@ char *btd_device_get_storage_path(struct btd_device *device, const char *name)
 
 void btd_device_device_set_name(struct btd_device *device, const char *name)
 {
+	size_t len;
+
 	if (strncmp(name, device->name, MAX_NAME_LENGTH) == 0)
 		return;
 
 	DBG("%s %s", device->path, name);
 
-	strncpy(device->name, name, MAX_NAME_LENGTH);
+	/*
+	 * Truncate on a character boundary, so that a name longer than
+	 * MAX_NAME_LENGTH does not end up with a partial sequence, which
+	 * would no longer be valid UTF-8 and would be rejected by D-Bus.
+	 */
+	len = strnlenutf8(name, MIN(strlen(name), (size_t) MAX_NAME_LENGTH));
+
+	memcpy(device->name, name, len);
+	device->name[len] = '\0';
 
 	store_device_info(device);
 
-- 
2.54.0