AD: Remember last site discovered

To discover Active Directory site for a client we must first contact any
directory controller for an LDAP ping. This is done by searching
domain-wide DNS tree which may however contain servers that are not
reachable from current site and than we face long timeouts or failure.

This patch makes sssd remember the last successfuly discovered site
and use this for DNS search to lookup a site and forest again similar
to what we do when ad_site option is set.

Resolves:
https://pagure.io/SSSD/sssd/issue/3265

1 files changed, 43 insertions, 1 deletions

diff --git a/src/providers/ad/ad_srv.c b/src/providers/ad/ad_srv.c
index ff01ee95c..be1ba0f23 100644
--- a/src/providers/ad/ad_srv.c
+++ b/src/providers/ad/ad_srv.c
@@ -481,6 +481,7 @@ struct ad_srv_plugin_ctx {
     const char *hostname;
     const char *ad_domain;
     const char *ad_site_override;
+    const char *current_site;
 };
 
 struct ad_srv_plugin_ctx *
@@ -518,6 +519,11 @@ ad_srv_plugin_ctx_init(TALLOC_CTX *mem_ctx,
         if (ctx->ad_site_override == NULL) {
             goto fail;
         }
+
+        ctx->current_site = talloc_strdup(ctx, ad_site_override);
+        if (ctx->current_site == NULL) {
+            goto fail;
+        }
     }
 
     return ctx;
@@ -527,6 +533,32 @@ fail:
     return NULL;
 }
 
+static errno_t
+ad_srv_plugin_ctx_switch_site(struct ad_srv_plugin_ctx *ctx,
+                              const char *new_site)
+{
+    const char *site;
+    errno_t ret;
+
+    if (new_site == NULL) {
+        return EOK;
+    }
+
+    if (ctx->current_site != NULL && strcmp(ctx->current_site, new_site) == 0) {
+        return EOK;
+    }
+
+    site = talloc_strdup(ctx, new_site);
+    if (site == NULL) {
+        return ENOMEM;
+    }
+
+    talloc_zfree(ctx->current_site);
+    ctx->current_site = site;
+
+    return EOK;
+}
+
 struct ad_srv_plugin_state {
     struct tevent_context *ev;
     struct ad_srv_plugin_ctx *ctx;
@@ -613,7 +645,7 @@ struct tevent_req *ad_srv_plugin_send(TALLOC_CTX *mem_ctx,
 
     subreq = ad_get_dc_servers_send(state, ev, ctx->be_res->resolv,
                                     state->discovery_domain,
-                                    state->ctx->ad_site_override);
+                                    state->ctx->current_site);
     if (subreq == NULL) {
         ret = ENOMEM;
         goto immediately;
@@ -709,6 +741,16 @@ static void ad_srv_plugin_site_done(struct tevent_req *subreq)
     backup_domain = NULL;
 
     if (ret == EOK) {
+        /* Remember current site so it can be used during next lookup so
+         * we can contact directory controllers within a known reachable
+         * site first. */
+        ret = ad_srv_plugin_ctx_switch_site(state->ctx, state->site);
+        if (ret != EOK) {
+            DEBUG(SSSDBG_CRIT_FAILURE, "Unable to set site [%d]: %s\n",
+                  ret, sss_strerror(ret));
+            goto done;
+        }
+
         if (strcmp(state->service, "gc") == 0) {
             if (state->forest != NULL) {
                 if (state->site != NULL) {