--- sys/kern/uipc_usrreq.c	2026-06-29 12:51:19.000000000 +0000
+++ /tmp/opencode/fixsrc/sys/kern/uipc_usrreq.c	2026-10-24 13:14:50.717342896 +0000
@@ -767,6 +767,11 @@
 			if (ssb_appendcontrol(&so2->so_rcv, m, control)) {
 				control = NULL;
 				m = NULL;
+			} else {
+				/* DF-2560 fix: failing append must dispose
+				 * the internalized rights (the cleanup
+				 * below only disposes when error != 0). */
+				error = ENOBUFS;
 			}
 		} else if (so->so_type == SOCK_SEQPACKET) {
 			sbappendrecord(&so2->so_rcv.sb, m);