Fix kadm5/gssrpc XDR double free [CVE-2014-9421]

[MITKRB5-SA-2015-001] In auth_gssapi_unwrap_data(), do not free
partial deserialization results upon failure to deserialize.  This
responsibility belongs to the callers, svctcp_getargs() and
svcudp_getargs(); doing it in the unwrap function results in freeing
the results twice.

In xdr_krb5_tl_data() and xdr_krb5_principal(), null out the pointers
we are freeing, as other XDR functions such as xdr_bytes() and
xdr_string().

ticket: 8056 (new)
target_version: 1.13.1
tags: pullup

src/lib/kadm5/kadm_rpc_xdr.c

@@ -320,6 +320,7 @@ bool_t xdr_krb5_tl_data(XDR *xdrs, krb5_tl_data **tl_data_head)
 	       free(tl);
 	       tl = tl2;
 	  }
+	  *tl_data_head = NULL;
 	  break;
 
      case XDR_ENCODE:
@@ -1096,6 +1097,7 @@ xdr_krb5_principal(XDR *xdrs, krb5_principal *objp)
     case XDR_FREE:
 	if(*objp != NULL)
 	    krb5_free_principal(context, *objp);
+	*objp = NULL;
 	break;
     }
     return TRUE;

src/lib/rpc/auth_gssapi_misc.c

@@ -322,7 +322,6 @@ bool_t auth_gssapi_unwrap_data(
      if (! (*xdr_func)(&temp_xdrs, xdr_ptr)) {
 	  PRINTF(("gssapi_unwrap_data: deserializing arguments failed\n"));
 	  gss_release_buffer(minor, &out_buf);
-	  xdr_free(xdr_func, xdr_ptr);
 	  XDR_DESTROY(&temp_xdrs);
 	  return FALSE;
      }