BUG/MEDIUM: resolvers: Don't release resolution from a requester callbacks
Another way to say it: "Safely unlink requester from a requester callbacks".
Requester callbacks must never try to unlink a requester from a resolution, for
the current requester or another one. First, these callback functions are called
in a loop on a request list, not necessarily safe. Thus unlink resolution at
this place, may be unsafe. And it is useless to try to make these loops safe
because, all this stuff is placed in a loop on a resolution list. Unlink a
requester may lead to release a resolution if it is the last requester.
However, the unkink is necessary because we cannot reset the server state
(hostname and IP) with some pending DNS resolution on it. So, to workaround
this issue, we introduce the "safe" unlink. It is only performed from a
requester callback. In this case, the unlink function never releases the
resolution, it only reset it if necessary. And when a resolution is found
with an empty requester list, it is released.
This patch depends on the following commits :
* MINOR: resolvers: Purge answer items when a SRV resolution triggers an error
* MINOR: resolvers: Use a function to remove answers attached to a resolution
* MINOR: resolvers: Directly call srvrq_update_srv_state() when possible
* MINOR: resolvers: Add function to change the srv status based on SRV resolution
All the series must be backported as far as 2.2. It fixes a regression
introduced by the commit b4badf720 ("BUG/MINOR: resolvers: new callback to
properly handle SRV record errors").
don't release resolution from requester cb
diff --git a/src/resolvers.c b/src/resolvers.c
index 4844d7f..dd4efc8 100644
--- a/src/resolvers.c
+++ b/src/resolvers.c
@@ -605,7 +605,7 @@
if (srv->srvrq == srvrq && srv->svc_port == item->port &&
item->data_len == srv->hostname_dn_len &&
!resolv_hostname_cmp(srv->hostname_dn, item->target, item->data_len)) {
- resolv_unlink_resolution(srv->resolv_requester);
+ resolv_unlink_resolution(srv->resolv_requester, 0);
srvrq_update_srv_status(srv, 1);
ha_free(&srv->hostname);
ha_free(&srv->hostname_dn);
@@ -684,7 +684,7 @@
/* Unlink A/AAAA resolution for this server if there is an AR item.
* It is usless to perform an extra resolution
*/
- resolv_unlink_resolution(srv->resolv_requester);
+ resolv_unlink_resolution(srv->resolv_requester, 0);
}
if (!srv->hostname_dn) {
@@ -1825,8 +1825,9 @@
/* Removes a requester from a DNS resolution. It takes takes care of all the
* consequences. It also cleans up some parameters from the requester.
+ * if <safe> is set to 1, the corresponding resolution is not released.
*/
-void resolv_unlink_resolution(struct resolv_requester *requester)
+void resolv_unlink_resolution(struct resolv_requester *requester, int safe)
{
struct resolv_resolution *res;
struct resolv_requester *req;
@@ -1844,6 +1845,15 @@
if (!LIST_ISEMPTY(&res->requesters))
req = LIST_NEXT(&res->requesters, struct resolv_requester *, list);
else {
+ if (safe) {
+ /* Don't release it yet. */
+ resolv_reset_resolution(res);
+ res->hostname_dn = NULL;
+ res->hostname_dn_len = 0;
+ resolv_purge_resolution_answer_records(res);
+ return;
+ }
+
resolv_free_resolution(res);
return;
}
@@ -2070,6 +2080,11 @@
/* Handle all expired resolutions from the active list */
list_for_each_entry_safe(res, resback, &resolvers->resolutions.curr, list) {
+ if (LIST_ISEMPTY(&res->requesters)) {
+ resolv_free_resolution(res);
+ continue;
+ }
+
/* When we find the first resolution in the future, then we can
* stop here */
exp = tick_add(res->last_query, resolvers->timeout.retry);
@@ -2118,6 +2133,11 @@
/* Handle all resolutions in the wait list */
list_for_each_entry_safe(res, resback, &resolvers->resolutions.wait, list) {
+ if (LIST_ISEMPTY(&res->requesters)) {
+ resolv_free_resolution(res);
+ continue;
+ }
+
exp = tick_add(res->last_resolution, resolv_resolution_timeout(res));
if (tick_isset(res->last_resolution) && !tick_is_expired(exp, now_ms))
continue;
@@ -2676,7 +2696,7 @@
ha_free(&s->resolv_ctx.hostname_dn);
s->resolv_ctx.hostname_dn_len = 0;
if (s->resolv_ctx.requester) {
- resolv_unlink_resolution(s->resolv_ctx.requester);
+ resolv_unlink_resolution(s->resolv_ctx.requester, 0);
pool_free(resolv_requester_pool, s->resolv_ctx.requester);
s->resolv_ctx.requester = NULL;
}