soc: apple: rtkit: Cut syslog messages after the first '\0'

Certain messages from DCP contain NUL bytes in the random data after the
NUL terminated syslog message. Since the syslog message ends with '\n'
this results in a dev_info() message terminated with two newlines and an
empty printed line in the kernel log.

Signed-off-by: Janne Grunau <j@jannau.net>

Author: jannau

drivers/soc/apple/rtkit.c

@@ -476,7 +476,7 @@ static void apple_rtkit_syslog_rx_log(struct apple_rtkit *rtk, u64 msg)
 
 	log_context[sizeof(log_context) - 1] = 0;
 
-	msglen = rtk->syslog_msg_size - 1;
+	msglen = strnlen(rtk->syslog_msg_buffer, rtk->syslog_msg_size - 1);
 	while (msglen > 0 &&
 		   should_crop_syslog_char(rtk->syslog_msg_buffer[msglen - 1]))
 		msglen--;