auth/munge - truncate FQDN to shortname for AllocNodes.

gethostbyaddr() can potentially return a fully-qualified domain name,
which breaks backwards compatibility with the shortname AllocNodes
expected pre 19.05.

Bug 7653.

NEWS

@@ -18,6 +18,9 @@ documents those changes that are of interest to users and administrators.
  -- slurmctld - fix memory leak when using DebugFlags=Reservation.
  -- Reset --mem and --mem-per-cpu options correctly when using --mem-per-gpu.
  -- Use correct function signature for step_set_env() in gres plugin interface.
+ -- Restore pre-19.05 hostname handling behavior for AllocNodes by always
+    truncating to just the host portion and dropping any domain name portion
+    returned by gethostbyaddr().
 * Changes in Slurm 19.05.3-2
 ============================

src/plugins/auth/munge/auth_munge.c

@@ -318,9 +318,13 @@ char *slurm_auth_get_host(slurm_auth_credential_t *cred)
 	he = get_host_by_addr((char *)&cred->addr.s_addr,
 			      sizeof(cred->addr.s_addr),
 			      AF_INET, (void *)&h_buf, sizeof(h_buf), &h_err);
-	if (he)
+	if (he && he->h_name) {
+		/* Truncate the hostname to a short name */
+		char *sep = strchr(he->h_name, '.');
+		if (sep)
+			*sep = '\0';
 		hostname = xstrdup(he->h_name);
-	else {
+	} else {
 		slurm_addr_t addr = { .sin_addr.s_addr = cred->addr.s_addr };
 		uint16_t port;
 		error("%s: Lookup failed: %s", __func__, host_strerror(h_err));