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, 13 insertions, 14 deletions

diff --git a/src/providers/data_provider_fo.c b/src/providers/data_provider_fo.c
index 54c0841f9..c66912d56 100644
--- a/src/providers/data_provider_fo.c
+++ b/src/providers/data_provider_fo.c
@@ -707,32 +707,31 @@ void reset_fo(struct be_ctx *be_ctx)
 }
 
 void be_fo_set_port_status(struct be_ctx *ctx,
+                           const char *service_name,
                            struct fo_server *server,
                            enum port_status status)
 {
-    struct be_svc_data *svc;
-    struct fo_service *fsvc;
-
-    fo_set_port_status(server, status);
+    struct be_svc_data *be_svc;
 
-    fsvc = fo_get_server_service(server);
-    if (!fsvc) {
-        DEBUG(SSSDBG_OP_FAILURE, ("BUG: No service associated with server\n"));
+    be_svc = be_fo_find_svc_data(ctx, service_name);
+    if (be_svc == NULL) {
+        DEBUG(SSSDBG_OP_FAILURE,
+              ("No service associated with name %s\n", service_name));
         return;
     }
 
-    DLIST_FOR_EACH(svc, ctx->be_fo->svcs) {
-        if (svc->fo_service == fsvc) break;
-    }
-
-    if (!svc) {
-        DEBUG(SSSDBG_OP_FAILURE, ("BUG: Unknown service\n"));
+    if (!fo_svc_has_server(be_svc->fo_service, server)) {
+        DEBUG(SSSDBG_OP_FAILURE,
+              ("The server %p is not valid anymore, cannot set its status\n"));
         return;
     }
 
+    /* Now we know that the server is valid */
+    fo_set_port_status(server, status);
+
     if (status == PORT_WORKING) {
         /* We were successful in connecting to the server. Cycle through all
          * available servers next time */
-        svc->first_resolved = NULL;
+        be_svc->first_resolved = NULL;
     }
 }