Index: lib/libc/sys/getsockopt.2
===================================================================
--- lib/libc/sys/getsockopt.2
+++ lib/libc/sys/getsockopt.2
@@ -28,7 +28,7 @@
 .\"     @(#)getsockopt.2	8.4 (Berkeley) 5/2/95
 .\" $FreeBSD$
 .\"
-.Dd June 03, 2020
+.Dd October 04, 2020
 .Dt GETSOCKOPT 2
 .Os
 .Sh NAME
@@ -177,6 +177,7 @@
 .It Dv SO_PROTOCOL Ta "get the protocol number for the socket (get only)"
 .It Dv SO_PROTOTYPE Ta "SunOS alias for the Linux SO_PROTOCOL (get only)"
 .It Dv SO_ERROR Ta "get and clear error on the socket (get only)"
+.It Dv SO_RERROR Ta "enables receive error reporting"
 .It Dv SO_SETFIB Ta "set the associated FIB (routing table) for the socket (set only)"
 .El
 .Pp
@@ -513,6 +514,13 @@
 the error status.
 It may be used to check for asynchronous errors on connected
 datagram sockets or for other asynchronous errors.
+.Dv SO_RERROR
+indicates that receive buffer overflows should be handled as errors.
+Historically receive buffer overflows have been ignored and programs
+could not tell if they missed messages or messages had been truncated
+because of overflows.
+Since programs historically do not expect to get receive overflow errors,
+this behavior is not the default.
 .Pp
 .Dv SO_LABEL
 returns the MAC label of the socket.
Index: sys/kern/uipc_sockbuf.c
===================================================================
--- sys/kern/uipc_sockbuf.c
+++ sys/kern/uipc_sockbuf.c
@@ -436,6 +436,30 @@
 	mtx_assert(SOCKBUF_MTX(&so->so_rcv), MA_NOTOWNED);
 }
 
+void
+soroverflow_locked(struct socket *so)
+{
+
+	SOCKBUF_LOCK_ASSERT(&so->so_rcv);
+
+	if (so->so_options & SO_RERROR) {
+		so->so_rerror = ENOBUFS;
+		sorwakeup_locked(so);
+	} else
+		SOCKBUF_UNLOCK(&so->so_rcv);
+
+	mtx_assert(SOCKBUF_MTX(&so->so_rcv), MA_NOTOWNED);
+}
+
+void
+soroverflow(struct socket *so)
+{
+
+	SOCKBUF_LOCK(&so->so_rcv);
+	soroverflow_locked(so);
+	mtx_assert(SOCKBUF_MTX(&so->so_rcv), MA_NOTOWNED);
+}
+
 /*
  * Wait for data to arrive at/drain from a socket buffer.
  */
Index: sys/kern/uipc_socket.c
===================================================================
--- sys/kern/uipc_socket.c
+++ sys/kern/uipc_socket.c
@@ -1954,12 +1954,19 @@
 		KASSERT(m != NULL || !sbavail(&so->so_rcv),
 		    ("receive: m == %p sbavail == %u",
 		    m, sbavail(&so->so_rcv)));
-		if (so->so_error) {
+		if (so->so_error || so->so_rerror) {
 			if (m != NULL)
 				goto dontblock;
-			error = so->so_error;
-			if ((flags & MSG_PEEK) == 0)
-				so->so_error = 0;
+			if (so->so_error)
+				error = so->so_error;
+			else
+				error = so->so_rerror;
+			if ((flags & MSG_PEEK) == 0) {
+				if (so->so_error)
+					so->so_error = 0;
+				else
+					so->so_rerror = 0;
+			}
 			SOCKBUF_UNLOCK(&so->so_rcv);
 			goto release;
 		}
@@ -2303,7 +2310,7 @@
 		while (flags & MSG_WAITALL && m == NULL && uio->uio_resid > 0 &&
 		    !sosendallatonce(so) && nextrecord == NULL) {
 			SOCKBUF_LOCK_ASSERT(&so->so_rcv);
-			if (so->so_error ||
+			if (so->so_error || so->so_rerror ||
 			    so->so_rcv.sb_state & SBS_CANTRCVMORE)
 				break;
 			/*
@@ -3044,6 +3051,7 @@
 		case SO_NOSIGPIPE:
 		case SO_NO_DDP:
 		case SO_NO_OFFLOAD:
+		case SO_RERROR:
 			error = sooptcopyin(sopt, &optval, sizeof optval,
 			    sizeof optval);
 			if (error)
@@ -3265,6 +3273,7 @@
 		case SO_NOSIGPIPE:
 		case SO_NO_DDP:
 		case SO_NO_OFFLOAD:
+		case SO_RERROR:
 			optval = so->so_options & sopt->sopt_name;
 integer:
 			error = sooptcopyout(sopt, &optval, sizeof optval);
@@ -3284,8 +3293,13 @@
 
 		case SO_ERROR:
 			SOCK_LOCK(so);
-			optval = so->so_error;
-			so->so_error = 0;
+			if (so->so_error) {
+				optval = so->so_error;
+				so->so_error = 0;
+			} else {
+				optval = so->so_rerror;
+				so->so_rerror = 0;
+			}
 			SOCK_UNLOCK(so);
 			goto integer;
 
@@ -3834,7 +3848,7 @@
 		kn->kn_flags |= EV_EOF;
 		kn->kn_fflags = so->so_error;
 		return (1);
-	} else if (so->so_error)	/* temporary udp error */
+	} else if (so->so_error || so->so_rerror)
 		return (1);
 
 	if (kn->kn_sfflags & NOTE_LOWAT) {
Index: sys/kern/uipc_usrreq.c
===================================================================
--- sys/kern/uipc_usrreq.c
+++ sys/kern/uipc_usrreq.c
@@ -1054,7 +1054,7 @@
 			m = NULL;
 			control = NULL;
 		} else {
-			SOCKBUF_UNLOCK(&so2->so_rcv);
+			soroverflow_locked(so2);
 			error = ENOBUFS;
 		}
 		if (nam != NULL)
Index: sys/net/raw_usrreq.c
===================================================================
--- sys/net/raw_usrreq.c
+++ sys/net/raw_usrreq.c
@@ -100,10 +100,10 @@
 			n = m_copym(m, 0, M_COPYALL, M_NOWAIT);
 			if (n) {
 				if (sbappendaddr(&last->so_rcv, src,
-				    n, (struct mbuf *)0) == 0)
-					/* should notify about lost packet */
+				    n, (struct mbuf *)0) == 0) {
+					soroverflow(last);
 					m_freem(n);
-				else
+				} else
 					sorwakeup(last);
 			}
 		}
@@ -111,9 +111,10 @@
 	}
 	if (last) {
 		if (sbappendaddr(&last->so_rcv, src,
-		    m, (struct mbuf *)0) == 0)
+		    m, (struct mbuf *)0) == 0) {
+			soroverflow(last);
 			m_freem(m);
-		else
+		} else
 			sorwakeup(last);
 	} else
 		m_freem(m);
Index: sys/netgraph/bluetooth/socket/ng_btsocket_hci_raw.c
===================================================================
--- sys/netgraph/bluetooth/socket/ng_btsocket_hci_raw.c
+++ sys/netgraph/bluetooth/socket/ng_btsocket_hci_raw.c
@@ -539,6 +539,7 @@
 
 				NG_FREE_M(m);
 				NG_FREE_M(ctl);
+				soroverflow(pcb->so);
 			}
 		}
 next:
Index: sys/netgraph/ng_socket.c
===================================================================
--- sys/netgraph/ng_socket.c
+++ sys/netgraph/ng_socket.c
@@ -982,7 +982,7 @@
 	/* Send it up to the socket. */
 	if (sbappendaddr_locked(&so->so_rcv, (struct sockaddr *)&addr, m,
 	    NULL) == 0) {
-		SOCKBUF_UNLOCK(&so->so_rcv);
+		soroverflow_locked(so);
 		TRAP_ERROR;
 		m_freem(m);
 		return (ENOBUFS);
Index: sys/netinet/ip_divert.c
===================================================================
--- sys/netinet/ip_divert.c
+++ sys/netinet/ip_divert.c
@@ -285,7 +285,7 @@
 			if (sbappendaddr_locked(&sa->so_rcv,
 			    (struct sockaddr *)&divsrc, m,
 			    (struct mbuf *)0) == 0) {
-				SOCKBUF_UNLOCK(&sa->so_rcv);
+				soroverflow_locked(sa);
 				sa = NULL;	/* force mbuf reclaim below */
 			} else
 				sorwakeup_locked(sa);
Index: sys/netinet/raw_ip.c
===================================================================
--- sys/netinet/raw_ip.c
+++ sys/netinet/raw_ip.c
@@ -260,11 +260,10 @@
 		SOCKBUF_LOCK(&so->so_rcv);
 		if (sbappendaddr_locked(&so->so_rcv,
 		    (struct sockaddr *)ripsrc, n, opts) == 0) {
-			/* should notify about lost packet */
+			soroverflow_locked(so);
 			m_freem(n);
 			if (opts)
 				m_freem(opts);
-			SOCKBUF_UNLOCK(&so->so_rcv);
 		} else
 			sorwakeup_locked(so);
 	} else
Index: sys/netinet/udp_usrreq.c
===================================================================
--- sys/netinet/udp_usrreq.c
+++ sys/netinet/udp_usrreq.c
@@ -377,7 +377,7 @@
 	so = inp->inp_socket;
 	SOCKBUF_LOCK(&so->so_rcv);
 	if (sbappendaddr_locked(&so->so_rcv, append_sa, n, opts) == 0) {
-		SOCKBUF_UNLOCK(&so->so_rcv);
+		soroverflow(so);
 		m_freem(n);
 		if (opts)
 			m_freem(opts);
Index: sys/netinet6/icmp6.c
===================================================================
--- sys/netinet6/icmp6.c
+++ sys/netinet6/icmp6.c
@@ -1977,13 +1977,11 @@
 				    &last->inp_socket->so_rcv,
 				    (struct sockaddr *)&fromsa, n, opts)
 				    == 0) {
-					/* should notify about lost packet */
+					soroverflow_locked(last->inp_socket);
 					m_freem(n);
 					if (opts) {
 						m_freem(opts);
 					}
-					SOCKBUF_UNLOCK(
-					    &last->inp_socket->so_rcv);
 				} else
 					sorwakeup_locked(last->inp_socket);
 				opts = NULL;
@@ -2023,7 +2021,7 @@
 			m_freem(m);
 			if (opts)
 				m_freem(opts);
-			SOCKBUF_UNLOCK(&last->inp_socket->so_rcv);
+			soroverflow_locked(last->inp_socket);
 		} else
 			sorwakeup_locked(last->inp_socket);
 		INP_RUNLOCK(last);
Index: sys/netinet6/ip6_input.c
===================================================================
--- sys/netinet6/ip6_input.c
+++ sys/netinet6/ip6_input.c
@@ -1576,6 +1576,7 @@
 	so =  inp->inp_socket;
 	if (sbappendaddr(&so->so_rcv, (struct sockaddr *)dst, NULL, m_mtu)
 	    == 0) {
+		soroverflow(so);
 		m_freem(m_mtu);
 		/* XXX: should count statistics */
 	} else
Index: sys/netinet6/raw_ip6.c
===================================================================
--- sys/netinet6/raw_ip6.c
+++ sys/netinet6/raw_ip6.c
@@ -212,6 +212,7 @@
 				if (sbappendaddr(&last->inp_socket->so_rcv,
 						(struct sockaddr *)&fromsa,
 						 n, opts) == 0) {
+					soroverflow(last->inp_socket);
 					m_freem(n);
 					if (opts)
 						m_freem(opts);
@@ -323,6 +324,7 @@
 		m_adj(m, *offp);
 		if (sbappendaddr(&last->inp_socket->so_rcv,
 		    (struct sockaddr *)&fromsa, m, opts) == 0) {
+			soroverflow(last->inp_socket);
 			m_freem(m);
 			if (opts)
 				m_freem(opts);
Index: sys/netinet6/send.c
===================================================================
--- sys/netinet6/send.c
+++ sys/netinet6/send.c
@@ -291,7 +291,7 @@
 	SOCKBUF_LOCK(&V_send_so->so_rcv);
 	if (sbappendaddr_locked(&V_send_so->so_rcv,
 	    (struct sockaddr *)&sendsrc, m, NULL) == 0) {
-		SOCKBUF_UNLOCK(&V_send_so->so_rcv);
+		soroverflow_locked(V_send_so);
 		/* XXX stats. */
 		m_freem(m);
 	} else {
Index: sys/netinet6/udp6_usrreq.c
===================================================================
--- sys/netinet6/udp6_usrreq.c
+++ sys/netinet6/udp6_usrreq.c
@@ -195,7 +195,7 @@
 	SOCKBUF_LOCK(&so->so_rcv);
 	if (sbappendaddr_locked(&so->so_rcv, (struct sockaddr *)&fromsa[0], n,
 	    opts) == 0) {
-		SOCKBUF_UNLOCK(&so->so_rcv);
+		soroverflow_locked(so);
 		m_freem(n);
 		if (opts)
 			m_freem(opts);
Index: sys/netipsec/keysock.c
===================================================================
--- sys/netipsec/keysock.c
+++ sys/netipsec/keysock.c
@@ -141,7 +141,6 @@
 static int
 key_sendup0(struct rawcb *rp, struct mbuf *m, int promisc)
 {
-	int error;
 
 	if (promisc) {
 		struct sadb_msg *pmsg;
@@ -165,11 +164,12 @@
 	    m, NULL)) {
 		PFKEYSTAT_INC(in_nomem);
 		m_freem(m);
-		error = ENOBUFS;
-	} else
-		error = 0;
+		soroverflow(rp->rcb_socket);
+		return ENOBUFS;
+	}
+
 	sorwakeup(rp->rcb_socket);
-	return error;
+	return 0;
 }
 
 /* so can be NULL if target != KEY_SENDUP_ONE */
Index: sys/sys/socket.h
===================================================================
--- sys/sys/socket.h
+++ sys/sys/socket.h
@@ -172,6 +172,7 @@
 #define	SO_TS_CLOCK	0x1017		/* clock type used for SO_TIMESTAMP */
 #define	SO_MAX_PACING_RATE	0x1018	/* socket's max TX pacing rate (Linux name) */
 #define	SO_DOMAIN	0x1019		/* get socket domain */
+#define	SO_RERROR	0x1020		/* keep track of receive errors */
 #endif
 
 #if __BSD_VISIBLE
Index: sys/sys/socketvar.h
===================================================================
--- sys/sys/socketvar.h
+++ sys/sys/socketvar.h
@@ -100,6 +100,7 @@
 	struct	protosw *so_proto;	/* (a) protocol handle */
 	short	so_timeo;		/* (g) connection timeout */
 	u_short	so_error;		/* (f) error affecting connection */
+	u_short so_rerror;		/* (f) error affecting connection */
 	struct	sigio *so_sigio;	/* [sg] information for async I/O or
 					   out of band data (SIGURG) */
 	struct	ucred *so_cred;		/* (a) user credentials */
@@ -266,7 +267,8 @@
 
 /* can we read something from so? */
 #define	soreadabledata(so) \
-	(sbavail(&(so)->so_rcv) >= (so)->so_rcv.sb_lowat ||  (so)->so_error)
+	(sbavail(&(so)->so_rcv) >= (so)->so_rcv.sb_lowat || \
+	(so)->so_error || (so)->so_rerror)
 #define	soreadable(so) \
 	(soreadabledata(so) || ((so)->so_rcv.sb_state & SBS_CANTRCVMORE))
 
@@ -480,6 +482,8 @@
 void	socantrcvmore_locked(struct socket *so);
 void	socantsendmore(struct socket *so);
 void	socantsendmore_locked(struct socket *so);
+void	soroverflow(struct socket *so);
+void	soroverflow_locked(struct socket *so);
 
 /*
  * Accept filter functions (duh).