Suggested feature and contribution

[Bron Gondwana]

On Fri, Jul 19, 2019, at 10:09, Bron Gondwana wrote:
> On Thu, Jul 18, 2019, at 19:09, Egoitz Aurrekoetxea wrote:
>> Good morning,
>> 
>> When using delete_delayed if someone removes a big folder (that one with more than 20 subfolders anywhere below it) in mboxlist_delayed_deletemailbox() only last 20 are preserved. We think it could be a good idea to preserve all and to have a parameter for configuring it. The reason for that, is that we use delete_delayed for storing the removed content remotely with the customer hired retention period in slow disk space. Perhaps could be a good idea something like : 
>> 
>> In mboxlist_delayed_deletemailbox() : 
>> 
>> *If (!preserve_delete_delayed_folders_always)*
>> *{*
>>  /* keep the last 19, so the new one is the 20th */
>>  for (i = 0; i < (int)existing.count - 19; i++) {
>>  const char *subname = strarray_nth(&existing, i);
>>  syslog(LOG_NOTICE, "too many subfolders for %s, deleting %s (%d / %d)",
>>  newname, subname, i+1, (int)existing.count);
>>  r = mboxlist_deletemailbox(subname, 1, userid, auth_state, NULL, 0, 1, 1,
>>  keep_intermediaries);
>>  if (r) goto done;
>>  }
>> *}*
> 
> Hmm.... yeah, OK. This is actually buggy in that case! The intended behaviour was to avoid a Denial of Service attack where you would create and delete the same mailbox name millions of times - however, the whole concept is bogus because there's nothing stopping somebody creating and deleting folder000001 through folderFFFFFF and creating the same attack.
> 
> I suggest that we just remove this whole silly check entirely, and if we want a similar level of attack protection we do something smarter like a quota for total folders+deleted folders that haven't been cleaned up yet - set it high enough that anybody hitting that is clearly doing something wrong, and require the administrator semi-manually clean up the deleted folders in order to re-allow folder creation.
> 
> Cheers,
> 
> Bron.

I've pushed commits to master and 3.0 to remove this check.

--
 Bron Gondwana, CEO, Fastmail Pty Ltd
 brong at fastmailteam.com

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