FO: Check server validity before setting status

The list of resolved servers is allocated on the back end context and
kept in the fo_service structure. However, a single request often
resolves a server and keeps a pointer until the end of a request and
only then gives feedback about the server based on the request result.

This presents a big race condition in case the SRV resolution is used.
When there are requests coming in in parallel, it is possible that an
incoming request will invalidate a server until another request that
holds a pointer to the original server is able to give a feedback.

This patch simply checks if a server is in the list of servers
maintained by a service before reading its status.

https://fedorahosted.org/sssd/ticket/1364

1 files changed, 8 insertions, 5 deletions

diff --git a/src/providers/fail_over.c b/src/providers/fail_over.c
index deb7d394c..8925e3586 100644
--- a/src/providers/fail_over.c
+++ b/src/providers/fail_over.c
@@ -1476,10 +1476,13 @@ void fo_reset_services(struct fo_ctx *fo_ctx)
     }
 }
 
-struct fo_service *
-fo_get_server_service(struct fo_server *server)
+bool fo_svc_has_server(struct fo_service *service, struct fo_server *server)
 {
-    if (!server) return NULL;
-    return server->service;
-}
+    struct fo_server *srv;
+
+    DLIST_FOR_EACH(srv, service->server_list) {
+        if (srv == server) return true;
+    }
 
+    return false;
+}