Software / code / prosody
Changeset
12115:94de6b7596cc
mod_tombstones: Remember deleted accounts #1307
Presence subscriptions are normally revoked on account deletion, which
informs the contact. Sometimes this notification gets lost e.g. due to
s2s problems. The accounts JID may also be present e.g. in MUC
affiliations, chat group member lists, pubsub subscriptions or other
systems. These may grant privileges which would fall to someone who
creates the same account again, which this module is meant to prevent.
| author | Kim Alvefur <zash@zash.se> |
|---|---|
| date | Thu, 23 Dec 2021 14:08:20 +0100 |
| parents | 12114:e32f90c81519 |
| children | 12116:efcf25ad5406 |
| files | CHANGES plugins/mod_tombstones.lua |
| diffstat | 2 files changed, 76 insertions(+), 0 deletions(-) [+] |
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--- a/CHANGES Wed Dec 22 22:13:03 2021 +0100 +++ b/CHANGES Thu Dec 23 14:08:20 2021 +0100 @@ -16,6 +16,7 @@ - mod_cron: One module to rule all the periodic tasks - mod_admin_shell: New home of the Console admin interface - mod_admin_socket: Enable secure connections to the Console +- mod_tombstones: Prevent registration of deleted accounts ### Security and authentication
--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/plugins/mod_tombstones.lua Thu Dec 23 14:08:20 2021 +0100 @@ -0,0 +1,75 @@ +-- TODO warn when trying to create an user before the tombstone expires +-- e.g. via telnet or other admin interface +local datetime = require "util.datetime"; +local errors = require "util.error"; +local jid_split = require"util.jid".split; +local st = require "util.stanza"; + +-- Using a map store as key-value store so that removal of all user data +-- does not also remove the tombstone, which would defeat the point +local graveyard = module:open_store(nil, "map"); + +local ttl = module:get_option_number("user_tombstone_expiry", nil); +-- Keep tombstones forever by default +-- +-- Rationale: +-- There is no way to be completely sure when remote services have +-- forgotten and revoked all memberships. + +module:hook_global("user-deleted", function(event) + if event.host == module.host then + local ok, err = graveyard:set(nil, event.username, os.time()); + if not ok then module:log("error", "Could store tombstone for %s: %s", event.username, err); end + end +end); + +-- Public API +function has_tombstone(username) + local tombstone, err = graveyard:get(nil, username); + + if err or not tombstone then return tombstone, err; end + + if ttl and tombstone + ttl < os.time() then + module:log("debug", "Tombstone for %s created at %s has expired", username, datetime.datetime(tombstone)); + graveyard:set(nil, username, nil); + return nil; + end + return tombstone; +end + +module:hook("user-registering", function(event) + local tombstone, err = has_tombstone(event.username); + + if err then + event.allowed, event.error = errors.coerce(false, err); + return true; + elseif not tombstone then + -- Feel free + return; + end + + module:log("debug", "Tombstone for %s created at %s", event.username, datetime.datetime(tombstone)); + event.allowed = false; + return true; +end); + +module:hook("presence/bare", function(event) + local origin, presence = event.origin, event.stanza; + + -- We want to undo any left-over presence subscriptions and notify the former + -- contact that they're gone. + -- + -- FIXME This leaks that the user once existed. Hard to avoid without keeping + -- the contact list in some form, which we don't want to do for privacy + -- reasons. Bloom filter perhaps? + if has_tombstone(jid_split(presence.attr.to)) then + if presence.attr.type == "probe" then + origin.send(st.error_reply(presence, "cancel", "gone", "User deleted")); + origin.send(st.presence({ type = "unsubscribed"; to = presence.attr.from; from = presence.attr.to })); + elseif presence.attr.type == nil or presence.attr.type == "unavailable" then + origin.send(st.error_reply(presence, "cancel", "gone", "User deleted")); + origin.send(st.presence({ type = "unsubscribe"; to = presence.attr.from; from = presence.attr.to })); + end + return true; + end +end, 1);
