Sssd: sssd: denial of service via responder connection retry loop during file descriptor exhaustion

A flaw was found in sssd. A local user can cause a Denial of Service (DoS) by exhausting the responder service's available file descriptors (system handles used for open connections). By opening and maintaining many concurrent connections to a responder socket while continuing to queue new connection attempts, an attacker can trigger an unthrottled retry loop. This condition leads to high CPU utilization and stalls the service, preventing legitimate identity and authentication requests from being processed.