security: limit the maximum password lenght to 72 characters to prevent possible

server side resource consumption attack.

- bcrypt heavy computation can lead to DOS using a very long password .eg 10**8 lenght.
- we allowed this on registration or on password update

rhodecode/model/forms.py

@@ -90,6 +90,7 b' def LoginForm():'
         password = v.UnicodeString(
             strip=False,
             min=3,
+            max=72,
             not_empty=True,
             messages={
                 'empty': _(u'Please enter a password'),
@@ -111,21 +112,21 b' def UserForm(edit=False, available_langu'
         if edit:
             new_password = All(
                 v.ValidPassword(),
-                v.UnicodeString(strip=False, min=6, not_empty=False)
+                v.UnicodeString(strip=False, min=6, max=72, not_empty=False)
             )
             password_confirmation = All(
                 v.ValidPassword(),
-                v.UnicodeString(strip=False, min=6, not_empty=False),
+                v.UnicodeString(strip=False, min=6, max=72, not_empty=False),
             )
             admin = v.StringBoolean(if_missing=False)
         else:
             password = All(
                 v.ValidPassword(),
-                v.UnicodeString(strip=False, min=6, not_empty=True)
+                v.UnicodeString(strip=False, min=6, max=72, not_empty=True)
             )
             password_confirmation = All(
                 v.ValidPassword(),
-                v.UnicodeString(strip=False, min=6, not_empty=False)
+                v.UnicodeString(strip=False, min=6, max=72, not_empty=False)
             )
 
         password_change = v.StringBoolean(if_missing=False)
@@ -207,11 +208,11 b' def RegisterForm(edit=False, old_data={}'
         )
         password = All(
             v.ValidPassword(),
-            v.UnicodeString(strip=False, min=6, not_empty=True)
+            v.UnicodeString(strip=False, min=6, max=72, not_empty=True)
         )
         password_confirmation = All(
             v.ValidPassword(),
-            v.UnicodeString(strip=False, min=6, not_empty=True)
+            v.UnicodeString(strip=False, min=6, max=72, not_empty=True)
         )
         active = v.StringBoolean(if_missing=False)
         firstname = v.UnicodeString(strip=True, min=1, not_empty=False)