Pass the exported blacklist to mintupdate-automation on stdin

usr/bin/mintupdate-automation

@@ -55,14 +55,15 @@ def do_disable(_automation_id):
             print("%s %s removed." % (name, filename))
 
 def add_user_blacklist(outfile):
-    import tempfile
+    # The user's blacklist arrives on stdin. Never read it from a shared
+    # location such as /tmp: another user could swap the file for a symlink
+    # while the authentication dialog is open.
+    if sys.stdin is None or sys.stdin.isatty():
+        return
     try:
-        infile = os.path.join(tempfile.gettempdir(), "mintUpdate/blacklist")
-        with open(infile, "r") as export:
-            with open(outfile, "a") as f:
-                for line in export:
-                    f.write(line)
-        os.remove(infile)
+        with open(outfile, "a") as f:
+            for line in sys.stdin:
+                f.write(line)
         print("User blacklist exported.")
     except:
         pass

usr/lib/linuxmint/mintUpdate/preferences.py

@@ -5,7 +5,6 @@
 import json
 import os
 import subprocess
-import tempfile
 
 import gi
 gi.require_version('Gtk', '3.0')
@@ -215,11 +214,9 @@ def _build_automation(self, builder):
                 section.add_row(switch)
 
     def _export_blacklist(self, widget):
-        filename = os.path.join(tempfile.gettempdir(), "mintUpdate/blacklist")
         blacklist = self.settings.get_strv("blacklisted-packages")
-        with open(filename, "w") as f:
-            f.write("\n".join(blacklist) + "\n")
-        subprocess.run(["pkexec", "/usr/bin/mintupdate-automation", "blacklist", "enable"])
+        subprocess.run(["pkexec", "/usr/bin/mintupdate-automation", "blacklist", "enable"],
+                       input="\n".join(blacklist) + "\n", text=True)
 
     def _set_auto_upgrade(self, widget, param):
         self._toggle_automation(widget, "upgrade")