Implement MAX_LISTNAME_LENGTH to avoid calculating on each web access.

3 files changed, 25 insertions, 4 deletions

diff --git a/Mailman/Defaults.py.in b/Mailman/Defaults.py.in
index 5e158e5b..fabd95bd 100755
--- a/Mailman/Defaults.py.in
+++ b/Mailman/Defaults.py.in
@@ -166,6 +166,15 @@ HTML_TO_PLAIN_TEXT_COMMAND = '/usr/bin/lynx -dump %(filename)s'
 # character that doesn't match this class.  Do not include '/' in this list.
 ACCEPTABLE_LISTNAME_CHARACTERS = '[-+_.=a-z0-9]'
 
+# The number of characters in the longest listname in the installation.  The
+# fix for LP: #1780874 truncates list names in web URLs to this length to avoid
+# a content spoofing vulnerability.  If this is left at its default value of
+# 0, the length of the longest listname is calculated on every web access.
+# This can have performance implications in installations with a very large
+# number of lists.  To use this feature to avoid the calculation, set this to
+# a number equal to the length of the longest expected valid list name.
+MAX_LISTNAME_LENGTH = 0
+
 # Shall the user's real names be displayed along with their email addresses
 # in list rosters?  Defaults to No to preserve prior behavior.
 ROSTER_DISPLAY_REALNAME = No
diff --git a/Mailman/Utils.py b/Mailman/Utils.py
index 47e4e5cc..10629fc4 100644
--- a/Mailman/Utils.py
+++ b/Mailman/Utils.py
@@ -292,11 +292,16 @@ def GetPathPieces(envar='PATH_INFO'):
                    remote)
         # Check for listname injections that won't be websafed.
         pieces = [p for p in path.split('/') if p]
-        # Get the longest listname or 20 if none.
-        if list_names():
-            longest = max([len(x) for x in list_names()])
+        # Get the longest listname or 20 if none or use MAX_LISTNAME_LENGTH if
+        # provided > 0.
+        if mm_cfg.MAX_LISTNAME_LENGTH > 0:
+            longest = mm_cfg.MAX_LISTNAME_LENGTH
         else:
-            longest = 20
+            lst_names = list_names()
+            if lst_names:
+                longest = max([len(x) for x in lst_names])
+            else:
+                longest = 20
         if pieces and len(pieces[0]) > longest:
             syslog('mischief',
                'Hostile listname: listname=%s: remote=%s', pieces[0], remote)
diff --git a/NEWS b/NEWS
index cfca39a2..2b6de6c0 100644
--- a/NEWS
+++ b/NEWS
@@ -14,6 +14,13 @@ Here is a history of user visible changes to Mailman.
       From: addresses listed or matching listed regexps.  This can be used
       to modify mail to addresses that don't accept external mail From:
       themselves.
+
+    - There is a new MAX_LISTNAME_LENGTH setting.  The fix for LP: #1780874
+      obtains a list of the names of all the all the lists in the installation
+      in order to determine the maximum length of a legitimate list name.  It
+      does this on every web access and on sites with a very large number of
+      lists, this can have performance implications.  See the description in
+      Defaults.py for more information.
   
   Bug Fixes and other patches