From 0efc0993ec5210c8cf5a98eb9c0220014e030fd6 Mon Sep 17 00:00:00 2001 From: Christopher Faulet Date: Thu, 11 Mar 2021 18:09:53 +0100 Subject: [PATCH] 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 --- include/haproxy/resolvers.h | 2 +- src/resolvers.c | 28 ++++++++++++++++++++++++---- src/server.c | 4 ++-- src/stream.c | 2 +- 4 files changed, 28 insertions(+), 8 deletions(-) diff --git a/include/haproxy/resolvers.h b/include/haproxy/resolvers.h index 34bc0fbf47..baf43d5b00 100644 --- a/include/haproxy/resolvers.h +++ b/include/haproxy/resolvers.h @@ -45,7 +45,7 @@ int resolv_get_ip_from_response(struct resolv_response *r_res, void resolv_purge_resolution_answer_records(struct resolv_resolution *resolution); int resolv_link_resolution(void *requester, int requester_type, int requester_locked); -void resolv_unlink_resolution(struct resolv_requester *requester); +void resolv_unlink_resolution(struct resolv_requester *requester, int safe); void resolv_trigger_resolution(struct resolv_requester *requester); enum act_parse_ret resolv_parse_do_resolve(const char **args, int *orig_arg, struct proxy *px, struct act_rule *rule, char **err); int check_action_do_resolve(struct act_rule *rule, struct proxy *px, char **err); diff --git a/src/resolvers.c b/src/resolvers.c index 4844d7f3f2..dd4efc8b96 100644 --- a/src/resolvers.c +++ b/src/resolvers.c @@ -605,7 +605,7 @@ static void resolv_check_response(struct resolv_resolution *res) 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 @@ static void resolv_check_response(struct resolv_resolution *res) /* 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 @@ int resolv_link_resolution(void *requester, int requester_type, int requester_lo /* 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 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 @@ void resolv_unlink_resolution(struct resolv_requester *requester) 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 @@ static struct task *process_resolvers(struct task *t, void *context, unsigned in /* 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 @@ static struct task *process_resolvers(struct task *t, void *context, unsigned in /* 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 @@ enum act_return resolv_action_do_resolve(struct act_rule *rule, struct proxy *px 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; } diff --git a/src/server.c b/src/server.c index b631a22820..be820e36d5 100644 --- a/src/server.c +++ b/src/server.c @@ -3294,7 +3294,7 @@ int srvrq_resolution_error_cb(struct resolv_requester *requester, int error_code for (s = srvrq->proxy->srv; s != NULL; s = s->next) { HA_SPIN_LOCK(SERVER_LOCK, &s->lock); if (s->srvrq == srvrq) { - resolv_unlink_resolution(s->resolv_requester); + resolv_unlink_resolution(s->resolv_requester, 1); srvrq_update_srv_status(s, 1); free(s->hostname); free(s->hostname_dn); @@ -3448,7 +3448,7 @@ int srv_set_fqdn(struct server *srv, const char *hostname, int resolv_locked) strcmp(resolution->hostname_dn, hostname_dn) == 0) goto end; - resolv_unlink_resolution(srv->resolv_requester); + resolv_unlink_resolution(srv->resolv_requester, 0); free(srv->hostname); free(srv->hostname_dn); diff --git a/src/stream.c b/src/stream.c index c27ea539c0..54c6a77bf5 100644 --- a/src/stream.c +++ b/src/stream.c @@ -674,7 +674,7 @@ static void stream_free(struct stream *s) HA_SPIN_LOCK(DNS_LOCK, &resolvers->lock); ha_free(&s->resolv_ctx.hostname_dn); s->resolv_ctx.hostname_dn_len = 0; - resolv_unlink_resolution(s->resolv_ctx.requester); + resolv_unlink_resolution(s->resolv_ctx.requester, 0); HA_SPIN_UNLOCK(DNS_LOCK, &resolvers->lock); pool_free(resolv_requester_pool, s->resolv_ctx.requester); -- 2.39.5