sparc: fix ldom_reboot buffer overflow harder

The length argument to strlcpy was still wrong. It could overflow the end of
full_boot_str by 5 bytes. Instead of strcat and strlcpy, just use snprint.
Reported-by: NBrad Spengler <spender@grsecurity.net>
Signed-off-by: NKees Cook <keescook@chromium.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

arch/sparc/kernel/ds.c

@@ -849,9 +849,8 @@ void ldom_reboot(const char *boot_command)
 	if (boot_command && strlen(boot_command)) {
 		unsigned long len;
 
-		strcpy(full_boot_str, "boot ");
-		strlcpy(full_boot_str + strlen("boot "), boot_command,
-			sizeof(full_boot_str));
+		snprintf(full_boot_str, sizeof(full_boot_str), "boot %s",
+			 boot_command);
 		len = strlen(full_boot_str);
 
 		if (reboot_data_supported) {